Childhood vaccinations

• Vaccination protects an individual against specific serious infections and, at population level, slows or stops transmission so that even unvaccinated people are protected.
• The routine US schedule covered here runs from birth to 18 years and includes hepatitis B, rotavirus, DTaP, Hib, pneumococcal conjugate, inactivated polio, influenza, MMR, varicella, hepatitis A, meningococcal, HPV and Tdap.
• Vaccines are of two main families: live, attenuated vaccines that must replicate to work and must not be given to most people with markedly weakened immunity, and non-live (inactivated, subunit, toxoid, conjugate, recombinant) vaccines that cannot cause infection and are safe in immunodeficiency. ^[5]
• Vaccines are contraindicated mainly by a severe allergic reaction to a previous dose or to a component; many other conditions are precautions rather than absolute barriers, and moderate or severe acute illness usually means deferral rather than permanent avoidance.
• When a child is late, do not restart the series: pick up from where it was interrupted and follow the minimum intervals in the catch-up schedule.
• Safety concerns such as thiomersal, aluminium adjuvants and MMR have been examined extensively; high-quality evidence shows no causal link between vaccines and autism.

By the end of this page you should be able to:

1. List the routine vaccines from birth to adolescence and the ages at which they are given.
2. Explain how live and inactivated vaccines differ in mechanism, dosing and storage, and which are live.
3. Screen a child before vaccination: identify true contraindications, precautions and conditions that defer immunisation. ^[4]
4. Plan catch-up immunisation for an under-immunised child without restarting the series.
5. Counsel families about common adverse effects and misconceptions using the evidence.
6. Adapt immunisation for a child who is immunocompromised or has asplenia, and explain herd immunity in clinical terms. ^[9]

This page is about the childhood immunisation procedure as a whole rather than one disease. It describes which vaccines are recommended during childhood and adolescence, how they are classified, how contraindications and catch-up work, what they can and cannot do, and how immunisation policy protects whole communities. It is a clinical and public-health procedure, so it is written for a clinician or student who will plan, document and counsel, and it is anchored to the United States schedule used here as the working example; national schedules elsewhere differ and should be used where you actually practise.

Several general principles make the whole schedule hang together. Vaccines are most often given in childhood because that is when vulnerability to these diseases is highest and because the immune system responds strongly. Most vaccines produce at least two benefits at once: individual protection and a reduced chance of transmission to others. Most non-live products need multiple doses to build and keep protection, whereas a single dose of most injected live vaccines is highly effective. Finally, safety is treated as part of the schedule itself rather than as an afterthought: every vaccine has a defined contraindication and precaution list, every clinically significant adverse event is reportable, and every family should receive the appropriate information before consent is taken. ^[4]

The words "vaccination" and "immunisation" are often used interchangeably, but they are not identical. Vaccination is the act of giving a vaccine. Immunisation is the process by which a person becomes protected, through vaccination or through natural infection. Giving a dose does not always produce protection in every individual, which is why coverage needs to be high rather than perfect in every single child.

Every childhood vaccine belongs to one of two families, and the distinction explains most of what looks like arbitrary variation between products. ^[5]

Live vaccines are made from the living, disease-causing organism that has been weakened (attenuated) in the laboratory until it no longer causes the natural disease in a healthy host. To produce an immune response it must actually replicate a little inside the recipient, so a small administered dose multiplies to the amount needed to trigger immunity. The immune response it produces resembles natural infection closely, including both antibody and cell-mediated immunity, so a single injection usually gives durable, long-lasting protection; a second dose exists mainly to capture the minority who did not respond the first time. Injected live vaccines in the US childhood schedule are MMR, varicella and the combination MMRV; rotavirus is an oral live vaccine and intranasal influenza (LAIV) is a live attenuated influenza vaccine. ^{[5] [4]}

Two consequences follow directly. First, live vaccines are fragile: they are damaged by heat and light, so the cold chain matters and they must be stored and handled exactly as the label instructs. Second, because the weakened organism can replicate without restraint in a host who cannot control it, live vaccines can cause severe or even fatal infection in a person with a markedly weakened immune system. That single fact is the basis of most live-vaccine contraindications. Orally administered live vaccines such as rotavirus need more than one dose to achieve immunity despite being live. ^[5]

Inactivated (non-live) vaccines are not alive and cannot replicate. They cannot cause disease even in an immunodeficient person, and they are less affected by circulating antibody than live vaccines, so they can be given in infancy or shortly after antibody-containing blood products. They include whole inactivated viruses (polio, hepatitis A, rabies), subunit vaccines (influenza, pneumococcal), toxoids (diphtheria and tetanus) and recombinant products (hepatitis B, HPV). Conjugate vaccines, such as Hib and pneumococcal conjugate, attach a bacterial polysaccharide to a protein carrier so that the infant immune system responds strongly. ^[5]

Inactivated vaccines generally need a primary series of several doses because the first dose usually primes the immune system without yet producing protection, and antibody titres fall over time, so boosters are needed for some. Their immune response is largely humoral, with little or no cellular immunity. Multiple non-live vaccines may always be given together at different anatomical sites, which is how the schedule administers several at a single visit without reducing responses. ^[5]

A practical rule that prevents most errors: if a vaccine is live, ask first whether the child (or someone in their close environment) is severely immunocompromised or pregnant; if a vaccine is non-live, give it regardless of immune status, although effectiveness may be reduced and extra doses may be needed.

The US schedule used here is that of the Advisory Committee on Immunization Practices (ACIP), approved by the Centers for Disease Control and Prevention (CDC) and the major professional societies, summarised in the schedule by age and its accompanying notes. Vaccine doses given up to 4 days before the minimum age or interval count as valid; doses given 5 or more days early should be treated as invalid and repeated at the proper interval. ^[1][2]

The following table collects the vaccines required by the brief. Age windows are routine recommendations for otherwise healthy children; special situations (medical conditions, travel, outbreaks) add further indications described in the notes and the sections below. ^[1][2]

A few details in these rows carry practical weight and are worth stating rather than being inferred from the table.

Hepatitis B is the only routine infant vaccine that starts at birth, because perinatal transmission carries the highest risk of chronic infection. The maternal HBsAg status changes the entire birth plan: a negative mother needs only the birth dose within 24 hours; a positive mother needs the birth dose plus HBIG within 12 hours in separate limbs; when the status is unknown the infant is managed as if the mother is positive until testing returns. Final doses are never given before 24 weeks of age, and infants of positive or unknown mothers are tested for HBsAg and antibodies at 9-12 months. ^[2]

Rotavirus timing is rigid for a biological reason: the vaccine must be started before 15 weeks of age and completed by 8 months, both because intussusception risk is age-related and because later doses are not studied. If the product given earlier is unknown, the default is the 3-dose product. ^[2][3]

DTaP dose 4 can be moved forward to 12 months if 6 months have elapsed since dose 3, and dose 5 is unnecessary if dose 4 was given at 4 years or older and at least 6 months after dose 3. For children under 7 years with a genuine contraindication to the pertussis component, Td (tetanus and diphtheria alone) is substituted for the remaining doses; encephalopathy within 7 days of a previous pertussis-containing dose, when not explained by another cause, is the only contraindication specific to the pertussis component. ^{[2] [4]}

Hib differs by product: a primary series of 3 doses followed by a booster with most products, or 2 doses plus a booster with PedvaxHIB; Vaxelis is not used as the booster dose. Pneumococcal conjugate follows the familiar 2, 4, 6 and 12-15 month pattern and underpins both direct protection against invasive disease and indirect protection of adults. ^[2]

Polio must be given as inactivated (IPV) in the US schedule; the last IPV dose must be on or after the fourth birthday and at least 6 months after the previous dose, so a third dose given below 4 years still needs that final dose. Oral polio vaccine is live and is no longer used in the United States. ^[2]

Influenza is annual because of antigenic drift. A child 6 months to 8 years who has received fewer than 2 doses before the current season, or whose history is unknown, needs 2 doses at least 4 weeks apart; all others receive 1. From 2024-25 onward the recommended formulations are trivalent. An egg allergy is not a contraindication to influenza vaccination: any age-appropriate product, egg-based or non-egg-based, may be used. LAIV (the live intranasal product) has its own contraindications and is avoided in children 2-4 years with wheezing, in asplenia, in marked immunocompromise, in pregnancy and in those needing a protected environment (see below). ^[2][4]

MMR and varicella are live and are given together at 12-15 months and 4-6 years. For dose 1 in children 12-47 months the two should be administered as separate injections (MMR and varicella) rather than the combination MMRV, with MMRV reserved for when parents or caregivers prefer it; if MMRV is used, the minimum interval between doses is 3 months rather than 4 weeks. Travel to areas where measles or other infections are endemic is a reason to give an early dose at 6-11 months, with revaccination at 12-15 months. ^[2]

Hepatitis A is a 2-dose series starting at 12-23 months, at least 6 months apart, and the catch-up runs through 18 years; travellers' infants aged 6-11 months receive one dose before departure and a 2-dose series later. Meningococcal ACWY starts at 11-12 years with a booster at 16, and earlier for high-risk conditions; meningococcal B is offered between 16 and 23 years under shared clinical decision-making, with a fixed 2- or 3-dose series for at-risk groups. HPV is 2 doses 6-12 months apart if started before 15 years, 3 doses thereafter, and always 3 doses in immunocompromise including HIV infection; it is routinely offered at 11-12 years and may be given from 9, and it is not given during pregnancy. Tdap is given at 11-12 years, one dose. ^[2]

The core principle is that a series is never restarted, no matter how much time has passed between doses: whatever doses were given still count, and the remaining doses are given using the catch-up schedule for the child's current age. ^[3]

Practical rules that implement this:

• Always pair Table 1 (by age) with the catch-up table for minimum intervals, and apply the notes, because special situations change both the intervals and the age limits.
• Use the child's current age to choose the correct row of the catch-up table, not their age when they started.
• Rotavirus is the exception to "just pick up and continue": it must be started before 15 weeks of age and finished by 8 months, and doses given later are not used.
• IPV needs a final dose on or after the fourth birthday if earlier doses were given too young or too close together.
• If a dose is given even slightly early it is still valid if it was no more than 4 days before the minimum age or interval; a dose 5 or more days early is invalid and must be repeated after the recommended minimum interval. ^[2]
• Give the doses a child is now eligible for today, licensed and separated by at least the minimum interval; do not deliberately delay one vaccine to bring it into line with another if the schedule allows both now.
• Document what was given, with product, batch number, site, date and provider, so that future doses and catch-up are built on correct information.

A contraindication means the vaccine must not be given; a precaution means deferral is usually appropriate unless the benefit of protection clearly outweighs the risk. The single most important contraindication shared by almost every vaccine is a severe allergic reaction (anaphylaxis) to a previous dose or to a component of it. A moderate or severe acute illness, with or without fever, is a precaution for nearly all products rather than a permanent reason to avoid them. ^[4]

Live vaccines carry extra contraindications that flow directly from their biology: severe immunodeficiency, pregnancy, and family history of altered immunocompetence that has not been excluded. Live attenuated influenza vaccine additionally should not be given to children 2-4 years old with a history of asthma or wheezing, to anyone with anatomic or functional asplenia, to immunocompromised children, in pregnancy, to those taking aspirin or salicylates, and to close contacts of people in a protected (reverse-isolation) environment. ^{[4] [6]}

Vaccine-specific points that are commonly tested and clinically useful:

• DTaP / Tdap: the only contraindication specific to the pertussis component is encephalopathy within 7 days of a previous dose of a pertussis-containing vaccine when no other cause is found. A history of Guillain-Barre syndrome within 6 weeks of tetanus toxoid, an Arthus-type hypersensitivity reaction, progressive or unstable neurological disease or uncontrolled seizures are precautions.
• DTaP may need to be withheld if there is a progressive neurological disorder, infantile spasms or uncontrolled epilepsy, until the condition is clarified and stabilised.
• Hib: contraindicated under 6 weeks of age; otherwise generally well tolerated. ^[4]
• Rotavirus: contraindicated in severe combined immunodeficiency (SCID) and in anyone with a history of intussusception; altered immunocompetence other than SCID, chronic gastrointestinal disease, spina bifida or bladder exstrophy (Rotarix) are precautions.
• MMR and MMRV: contraindicated in severe immunodeficiency (haematological and solid tumours, chemotherapy, congenital immunodeficiency, long-term immunosuppressive therapy, or severe HIV disease), in pregnancy, and when there is a family history of altered immunocompetence that has not been ruled out. MMRV specifically is contraindicated in HIV infection of any severity. Precautions include recent receipt of antibody-containing blood products (with product-specific intervals), a history of thrombocytopenia or thrombocytopenic purpura, and the need for tuberculin or interferon-gamma release assay testing.
• Varicella and MMRV share the same severe-immunodeficiency and pregnancy contraindications. Receiving specific antivirals within 24 hours before vaccination (avoid for 14 days after), use of aspirin or salicylates, and MMRV-specific precautions (personal or family history of seizures) also apply. ^[4]
• Hepatitis B: contraindicated after a severe allergic reaction, including to yeast; PreHevbrio is not recommended in pregnancy because of a lack of safety data.
• HPV: contraindicated after a severe allergic reaction; not recommended during pregnancy (no action is needed if a dose is given inadvertently). ^[2]
• Inactivated polio: pregnancy is a precaution; severe allergic reaction to a component (including neomycin, streptomycin and polymyxin B) is a contraindication.
• Hepatitis A: severe allergy to a component, including neomycin, is a contraindication.
• Meningococcal: severe allergy to a component is a contraindication; MenB additionally carries pregnancy as a precaution. MenACWY-CRM is contraindicated in severe allergy to diphtheria toxoid or CRM197, and MenACWY-TT in severe allergy to a tetanus toxoid-containing vaccine.
• Dengue vaccine: contraindicated in severe immunodeficiency and when there is no laboratory confirmation of prior dengue infection; pregnancy is a precaution.
• Meningococcal ACWY in young infants: Menveo is deferred below 9 months of age in preterm infants.

Most injected vaccines are administered intramuscularly; the exceptions their labels specify (for example oral rotavirus, intranasal influenza, subcutaneous MMR and varicella, oral typhoid) are always stated on the product. The essential procedural steps before every injection are to confirm the patient's identity, review the record and the due doses, screen with the same contraindication and precaution questions every time, verify the product and that the cold chain has been maintained, obtain informed consent, administer, observe for the local interval your service uses, and record product, batch number, site, route, dose, date and provider. ^[5][4]

A true contraindication is rare; far more often the right action is to defer until recovery from an acute illness, or to give the appropriate non-live product instead of a live one. When in doubt, the specific vaccine's notes and appendix in the schedule are the authoritative reference for that product. ^[4]

Most immunisation reactions are mild, local and short-lived: pain, redness or swelling where the injection was given, a low-grade fever and fussiness for 1-2 days. Site reactions are expected and treatable (cool compress, analgesia). Serious adverse events are rare. An adverse event following immunisation (AEFI) is any unexpected medical problem that happens after a vaccine; it is not the same as an adverse reaction caused by the vaccine, and many AEFIs are coincidental. ^[7][9]

Product-specific effects that are worth knowing because families will ask:

• Injected vaccines commonly produce local reactions and occasional mild fever; these resolve within a day or two.
• Live attenuated products can cause very mild versions of the disease they protect against (a faint rash after varicella, or a brief mild fever).
• MMR has been associated, rarely, with febrile seizures and transient thrombocytopenia.
• Rotavirus is associated with a small increased risk of intussusception; this is the reason for the strict age limits rather than an argument against use.
• Influenza: a history of Guillain-Barre syndrome within 6 weeks of a previous influenza dose is a precaution, not an absolute contraindication.
• LAIV is a cold-adapted, temperature-sensitive intranasal product that replicates in the nasopharynx; children can shed it for up to 3 weeks, and transmission has been documented without causing serious illness. Contacts of severely immunocompromised people in a protected environment should avoid LAIV as above.
• COVID-19 and influenza vaccines in pregnancy are handled by the specific product notes; HPV and Tdap guidance for pregnant adolescents is covered in the notes.

Severe allergic reactions (anaphylaxis) are very rare but the reason every vaccination setting must have adrenaline and trained staff. Clinically significant adverse events and suspected cases of vaccine-preventable disease or outbreaks are reported to the Vaccine Adverse Event Reporting System (VAERS) and to the local health department. ^{[2][4][7] [3]}

VAERS is a passive reporting system: it is excellent for signal detection and poor for proving causation. When a signal appears, it is investigated through active surveillance and large linked studies before any change in policy.

This section is deliberately source-heavy, because these are the questions that determine whether families come back for the next dose. ^[7][8]

Vaccines do not cause autism. Extensive research over many years, in multiple countries and populations, using many study designs, has found no causal link between any childhood vaccine (including measles-mumps-rubella, thiomersal-containing vaccines and aluminium-adjuvanted vaccines) and autism spectrum disorder. A 1998 study that suggested an MMR-autism link was retracted by the journal that published it and its author lost his medical licence for misconduct. Every major systematic review of the strongest available evidence, including reviews of publications from 2010-2025 by the WHO Global Advisory Committee on Vaccine Safety, concludes that vaccines do not cause autism. ^[8]

Thiomersal (thimerosal) is not a risk. Thiomersal is a preservative used in multi-dose vials to prevent microbial contamination; it contains ethylmercury, a different compound from the methylmercury in some fish, and is rapidly broken down and removed rather than accumulating. It has been used safely since the 1930s, thiomersal was removed from almost all childhood vaccines in the United States in 2001, MMR, IPV, varicella and pneumococcal conjugate never contained it, and the yearly influenza vaccine is available both with and without thiomersal. An increase in autism diagnoses continued after thiomersal was withdrawn, which is the opposite of what would be expected if it caused autism. ^[7][8]

Aluminium adjuvants are not harmful. Aluminium salts (aluminium hydroxide or aluminium phosphate) are added to boost the immune response so that less antigen is needed. The amount of aluminium contributed by the entire childhood schedule is far below the amounts encountered in food and over time in daily life. High-quality studies, including a study of over one million children, have found no association between aluminium-adjuvanted vaccination and serious health problems or neurodevelopmental disorders including autism. ^[8]

“Too many, too soon” is not a problem. The number of antigens in modern vaccines is smaller than it was a generation ago, because each vaccine now contains only what is needed. A child’s immune system responds to thousands of antigens daily; combination vaccines produce protection against each component without blunting responses to the others, and they reduce the number of injections required. Delaying vaccines does not make them safer; it leaves the child exposed to the disease for longer. ^[7]

“Natural infection is better than vaccination” is wrong. Natural infection can certainly immunise, but it does so at the cost of the disease and its complications (pneumonia, encephalitis, congenital infection, death). Vaccines reproduce the protective part without the illness. ^[9]

Vaccines do not contain toxins in harmful amounts. Residual amounts of formaldehyde or other inactivating agents and antibiotics (neomycin, kanamycin, streptomycin) used in production remain well below levels that occur naturally in the body or in food. Antibiotics associated with common allergy, such as penicillin, are not used. Gelatin, sugars and buffers are stabilisers and are familiar food components. Thiomersal appears only in some multi-dose influenza vials. The statement on every product insert lists the ingredients. ^[7]

Safety is also a system, not a claim: the US vaccine safety programme combines pre-licensure trials, manufacturing quality, post-marketing surveillance through VAERS, the Vaccine Safety Datalink, the Clinical Immunization Safety Assessment network and the National Vaccine Injury Compensation Program, and other countries run equivalents. ^[7][2]

This is the part of the topic where the live versus non-live distinction becomes action. The assessment of the degree of immunosuppression is a clinical judgement, and infectious-disease or immunology input is valuable when it is uncertain, but the following points hold for routine decisions. ^[6]

• Non-live vaccines can be given safely to anyone with altered immunocompetence; the concern with them is effectiveness during immunosuppression, not safety. ^[6]
• Most forms of altered immunocompetence are a contraindication to live vaccines (MMR, varicella, MMRV, LAIV, yellow fever, oral typhoid, BCG, smallpox, rotavirus) because of the risk of uncontrolled replication.
• Persons with severe antibody deficiency or severe cellular immunodeficiency should not receive live bacterial or viral vaccines and may not respond to non-live vaccines that depend on humoral immunity.
• HIV-infected children who are not severely immunocompromised (CD4 percentages at least 15 percent for 6 months, and for children over 5 years CD4 counts at least 200 cells per mm3 for 6 months) should receive MMR, usually two doses; single-component varicella may be considered for eligible children from 12 months; MMRV is never given to a person with HIV infection. Yellow fever vaccine has its own CD4-based contraindication. ^[6]
• Children with complement deficiency should receive routine live vaccines as indicated, and complement-deficient persons receive meningococcal conjugate and MenB vaccines.
• Children with asplenia (surgical or functional, including sickle cell disease) must not receive LAIV but can take other live vaccines; they receive pneumococcal (PCV then PPSV23 from 2 years), Hib (with additional doses), and meningococcal ACWY and MenB with the extended schedules given in the notes above.
• Rotavirus and BCG are never given after a haematopoietic stem cell transplant (HSCT).
• HSCT recipients are revaccinated as though unimmunised: non-live vaccines (pneumococcal, DTaP, Tdap, Hib, hepatitis A and B, IPV, inactivated influenza, meningococcal conjugate, MenB, HPV) start about 6 months after transplant, and inactivated influenza annually thereafter; MMR and varicella can be given about 24 months after transplant if there is no graft-versus-host disease and the patient is considered immunocompetent.
• Corticosteroids at about 2 mg per kg (or 20 mg per day of prednisone or equivalent) for 14 or more consecutive days are sufficiently immunosuppressive to defer live vaccines for at least 1 month after stopping; short courses, low doses and topical, inhaled or intra-articular preparations are not a contraindication. Live vaccines are withheld for 3 months after chemotherapy or radiotherapy and for about 2 months after stopping anti-rejection or other immunomodulating therapy, and for 6 months after anti-B-cell agents for non-live vaccines. ^[6]
• Children on immunoglobulin therapy or anti-B-cell agents (such as rituximab) should not receive either live or non-live vaccines while on therapy; a minimum wait (about 6 months for anti-B-cell agents) applies and, where immunoglobulin is the issue, MMR or varicella can sometimes be timed before the next immunoglobulin dose and then repeated later. Laboratory tests (immunoglobulin levels, CD4 counts) help quantify the degree of impairment.
• Non-live vaccines given during immunosuppression produce suboptimal responses; anyone vaccinated within 14 days before starting immunosuppressive therapy, or during therapy, should be regarded as unimmunised and revaccinated at least 3 months after therapy stops if competence has been restored. Non-live vaccines unrelated to influenza are best given before immunosuppression starts if there is time. ^[6]
• Household and other close contacts of an immunocompromised person should be fully vaccinated, including with live MMR, varicella and rotavirus, because vaccinating the contacts prevents them from bringing infection home. Varicella vaccine recipients who develop a post-vaccination rash should avoid direct contact with susceptible immunocompromised household members until it resolves, oral rotavirus recipients need careful hand hygiene for up to 1 month after the last dose because of shedding, and LAIV should not be given to healthy contacts if the vulnerable person is in a protected environment (otherwise inactivated influenza is preferred for them). ^[6]

The table below is adapted from the standard summary of vaccination in immunodeficiency; it is not a substitute for the individual product notes or specialist advice. ^[6]

Immunisation differs from most medical treatments because it also changes the environment. When a large enough share of a population is immune, infection cannot circulate freely and the unvaccinated are protected indirectly. This indirect protection, called community or herd immunity, is why a child too young to be fully vaccinated (a 2-month-old, for instance) is safer in a community with 95 percent coverage than in one with 80 percent. ^[9]

The required proportion varies with how contagious the agent is. Measles is highly contagious and herd immunity there exceeds 90 percent and in practice roughly 95 percent; poliomyelitis needs on the order of 80 percent. The threshold is the point at which the effective reproduction number falls below one and outbreaks stop. Lower coverage still gives some indirect benefit (every vaccinated person is less likely to transmit), but the community protection is lost below the threshold. ^[9]

Three consequences change clinical practice. First, high coverage is in everyone's interest, including those who are not vaccinated, because it is the protection for those who cannot be vaccinated (neonates, immunocompromised patients, pregnant women). Second, coverage gaps produce outbreaks: the resurgence of measles in a community is almost always a coverage failure rather than a vaccine failure. Third, a decision to decline vaccination free-rides on the immunity of others; as more families do so, the common protection erodes and disease returns, affecting those who had no choice in the matter. This is the "tragedy of the commons" in immunisation and it is the rationale behind scheduled school entry requirements in many countries (regional rules vary).

Herd immunity is not sterile, permanent protection for an individual; it reduces the probability of exposure. Individuals still need their own immunisation record, and some vaccine-derived protection wanes, which is why boosters for pertussis, tetanus and influenza exist.

Immunisation policy is set nationally, not by any universal schedule. The schedule above is the US working example; the WHO Expanded Programme on Immunization and national programmes include additional vaccines (such as BCG and, in many regions, yellow fever and oral polio) with their own timing, and local cold-chain rules may differ. Use the national schedule of the place where the child is being seen, catch up to that schedule, and refer to the national guidelines and the primary-care clinician for any immunocompromised child.

Access and cold chain matter as much as the schedule itself: most EPI vaccines need the right temperature from manufacturer to arm, and oral rotavirus in particular is sensitive. Missed opportunities are a bigger problem than rare contraindications in every setting; the default should be to give everything due at every visit rather than to defer by habit. Parent-held records and defaulter tracing (using registries and community health workers) are the operational core of a good programme.

Escalate when a child has a true contraindication to a vaccine rather than a precaution, when an immunocompromised child needs a live vaccine decision, when there is a serious adverse event (any suspected anaphylaxis, encephalopathy or seizure after vaccination, a high fever with inconsolable crying, intussusception after rotavirus), when a child is substantially behind and the catch-up exceeds the age limits (for example rotavirus), and whenever a parent's question goes beyond the evidence you can defend. Report any serious AEFI and any suspected outbreak. ^[4]

• Childhood immunisation runs from birth to adolescence and, in the working example used here, covers hepatitis B, rotavirus, DTaP, Hib, pneumococcal conjugate, inactivated polio, influenza, MMR, varicella, hepatitis A, meningococcal, HPV and Tdap.
• There are two vaccine families: live, attenuated vaccines that must replicate and are contraindicated in most severe immunodeficiency and in pregnancy; and non-live (killed, subunit, toxoid, conjugate, recombinant) vaccines that cannot cause infection and are safe in immunodeficiency, though they may need boosters.
• The schedule is a by-age table plus product-specific notes, catch-up rules and an appendix; doses may count if given up to 4 days early but must be repeated if given 5 or more days early.
• Hepatitis B is the infant birth dose and its birth management depends on maternal HBsAg status.
• Measles (MMR) and varicella are live and are given together; MMRV has a 3-month minimum interval between doses and is avoided in HIV infection.
• Rotavirus has hard age limits (start before 15 weeks, finish by 8 months) because of intussusception risk; IPV needs a final dose on or after the fourth birthday. ^[3]
• A contraindication is usually a severe allergic reaction to a previous dose or component, or severe immunodeficiency for live vaccines; most other conditions are precautions or reasons to defer while acutely ill.
• Catch-up never restarts a series; use the child's current age and respect minimum ages and intervals. Do not routinely delay available doses to align schedules.
• Common adverse effects are mild and brief; anaphylaxis is very rare; serious events and suspected disease or outbreaks are reported.
• Thiomersal, aluminium adjuvants, and MMR do not cause autism; high-quality international reviews confirm this; multi-dose influenza vials sometimes contain thiomersal and thiomersal-free options exist.
• Live vaccines are withheld in severe immunodeficiency and often deferred during high-dose steroids, chemotherapy or anti-lymphocyte therapy; non-live vaccines are safe but may need repeating after immune restoration.
• Household contacts of immunocompromised children should be fully immunised, including with live vaccines, to prevent bringing infection into the home.
• Community (herd) immunity depends on coverage: over 90% (about 95%) for measles and roughly 80% for polio in principle, and outbreaks occur when coverage falls.

• Infectious-disease immunisation (adult and outbreak immunisation, vaccine strategies and adverse-event surveillance). Cross-check the principles in this page with that topic.
• Immune thrombocytopenia, primary immunodeficiency disorders, childhood leukaemia (states where live vaccines are withheld and non-live vaccines timed carefully).
• Pneumococcal infection, meningococcal disease, pertussis, measles, varicella, hepatitis B, hepatitis A, human papillomavirus infection, and influenza (the diseases the vaccines prevent).
• Haemolytic anaemias and sickle cell disease (asplenia and functional asplenia).
• Congenital TORCH infections and Epstein-Barr virus/infectious mononucleosis (where maternal immunisation and infant protection interact).