TABLE 1. Recommendations for interrupted or delayed childhood immunization schedule: simplified table.

Vaccine		Doses in primary series (minimum interval between doses)	Dosage for those who start the delayed scheme
			If ≤12 months	If >12 months	Vaccine booster
BCG1		1 dose as soon as possible after birth	1 dose	1 dose Administer one dose of the vaccine for up to age 4 years, 11 months, and 29 days	Not recommended
Hepatitis B2		Birth dose <24 hours plus 2–3 doses with DTPCV (4 weeks)	3 doses	3 doses	Not recommended
Polio3	bOPV + IPV	5 doses (3 bOPV and 2 IPV)	5 doses (IPV to be given with 1st dose & 3rd dose of bOPV)	5 doses (IPV to be given with 1st dose & 3rd dose of bOPV)	Not recommended
	IPV/bOPV sequential	1–2 doses IPV and 2 doses bOPV (4 weeks)	1–2 doses IPV and 2 doses bOPV	1–2 doses IPV and 2 doses bOPV	Not recommended
	IPV	3 doses (4 weeks)	3 doses	3 doses	If the primary series begins <2 months of age, booster to be given at least 6 months after the last dose
DTP-containing vaccine (DTPCV)4		3 doses (4 weeks)	3 doses	3 doses with interval of at least 4 weeks between 1st & 2nd dose, and at least 6 months between 2nd & 3rd dose (if >7 years use only aP-containing vaccine; if >4 years, Td-containing vaccine is preferred and should only be used for >7 years)	3 boosters: 1–23 months (DTP-containing vaccine); 4–7 years (Td/DT-containing vaccine), see footnotes; 9–15 years (Td-containing vaccine; if >7 years use only aP-containing vaccine) If tetanus vaccination started during adolescence or adulthood, only 5 doses are required for lifelong protection
Haemophilus influenzae type b5	Option 1	3 doses (4 weeks)	3 doses	1 dose >5 years not recommended if healthy	Not recommended
	Option 2	2–3 doses (8 weeks if 2 doses; 4 weeks if 3 doses)	2–3 doses (8 weeks if 2 doses; 4 weeks if 3 doses)		At least 6 months after last dose
Pneumococcal conjugate6		3 doses (3p+0) with DTPCV (4 weeks) or 2 doses (2p+1) (8 weeks)	2–3 doses	1–5 years at high risk: 2 doses	Booster at 9–18 months if following 2-dose schedule Another booster if HIV+ or preterm neonate Vaccination in older adults
Rotavirus7		2 or 3 depending on product given with DTPCV	2 or 3 depending on product	>24 months limited benefit	Not recommended
Meningococcal8	MenA conjugate	1 dose if ≥9 months 2 doses if <9 months with 8-week interval	2 doses if <9 months with 8-week interval	1 dose of 5μg up to 24 months	Not recommended
	MenC conjugate	2 (8 weeks)	2 doses	1 dose	1 dose after 1 year of age for those who received the 2-dose infant primary immunization
	MenACWY conjugate	2 (8–12 weeks)	2 doses	1 dose	1 dose after 1 year of age for those who received the 2-dose infant primary immunization
Yellow fever9		1 dose In Brazil: 1st dose at 9 months Booster at 4 years of age	1 dose	1 dose	Not recommended
Measles mumps rubella10		2 doses (4 weeks)	2 doses	2 doses	Not recommended
Vaccine		Doses in primary series (minimum interval between doses)	Dosage for those who start the delayed scheme
			If ≤12 months	If >12 months	Vaccine booster
Varicela11		1–2 doses (4 weeks to 3 months, depending on manufacturer)	Not recommended	1–2 doses	Not recommended
Hepatitis A12		At least 1 dose (minimum 1 year of age)	Not recommended	At least 1 dose	Not recommended

BCG, bacillus Calmette–Guérin; bOPV, bivalent oral polio vaccine; DTP, diphtheria tetanus pertussis; DTPCV, diphtheria tetanus pertussis-containing vaccine; HIV, human immunodeficiency virus; IPV, inactivated polio vaccine.

Notes:

¹BCG vaccination is recommended for unvaccinated tuberculin skin test (TST)-negative or interferon-gamma release assay (IGRA)-negative older children, adolescents, and adults from settings with high incidence of tuberculosis (TB) and/or high leprosy burden and those moving from low to high TB incidence/leprosy burden settings.

²If delayed or interrupted scheduling of vaccination for children, adolescents, and adults, 3 doses are recommended, with the second dose administered at least 1 month after the first, and the third dose 6 months after the first dose. If the vaccination schedule is interrupted it is not necessary to restart the vaccine series.

³All countries that currently administer three bOPV and one IPV dose should add a second IPV dose in their routine immunization schedule (Oct 2020 SAGE Meeting Report). Regardless of the 2-dose IPV schedule used, introduction of the second IPV dose does not reduce the number of bOPV doses (three) used in the routine immunization schedule (Oct 2020 SAGE Meeting Report).

⁴If either the start or the completion of the primary series has been delayed, the missing doses should be given at the earliest opportunity with an interval of at least 4 weeks between doses.

Three booster doses of diphtheria toxoid-containing vaccine should be provided during childhood and adolescence. The diphtheria booster doses should be given in combination with tetanus toxoid using the same schedule; i.e., at 12–23 months of age, 4–7 years of age, and 9–15 years of age, using age-appropriate vaccine formulations. Ideally, there should be at least 4 years between booster doses.

Tetanus: To ensure lifelong protection against tetanus all people should receive 6 doses (3 primary plus 3 booster doses) of tetanus toxoid-containing vaccine (TTCV) through routine childhood immunization schedules.

If tetanus vaccination is started during adolescence or adulthood, a total of only 5 appropriately spaced doses are required to obtain lifelong protection.

To provide and sustain both tetanus and diphtheria immunity throughout the life course and for both sexes, age-appropriate combinations of tetanus and diphtheria toxoids should be used. For children <7 years of age DTwP or DTaP combinations may be used. For children aged 4 years and older Td-containing vaccine may be used and is preferred.

From 7 years of age only Td combinations should be used. Age-appropriate combinations containing pertussis vaccine with low-dose diphtheria antigen are also available.

Pregnant women and their newborn infants are protected from birth-associated tetanus if the mother received either 6 TTCV doses during childhood or 5 doses if first vaccinated during adolescence/adulthood (documented by card, immunization registry, and/or history) before the time of reproductive age. Vaccination history should be verified in order to determine whether a dose of TTCV is needed in the current pregnancy.

Pertussis vaccine: Only aP-containing vaccines should be used for vaccination of persons aged ≥7 years.

Pertussis containing booster: A booster dose is recommended for children aged 1–6 years, preferably during the second year of life (≥6 months after last primary dose), unless otherwise indicated by local epidemiology; the contact could also be used to catch up on any missed doses of other vaccines. This schedule should provide protection for at least 6 years for countries using wP vaccine. For countries using aP vaccine, protection may decline appreciably before 6 years of age.

Delayed or interrupted DTP-containing series: For children whose vaccination series has been interrupted, the series should be resumed without repeating previous doses. Children aged 1 to <7 years who have not previously been vaccinated should receive 3 doses of vaccine following a 0, 1, 6 month schedule. Two subsequent booster doses using Td or Tdap combination vaccines are needed with an interval of at least 1 year between doses.

⁵The number of primary doses should be set after consideration of the local epidemiology, vaccine presentation (Hib conjugate monovalent vaccine versus Hib conjugate vaccine in combination with other antigens), and how this fits into the overall routine immunization schedule.

If the vaccination course has been interrupted, the schedule should be resumed without repeating the previous dose. Children who start vaccination late, but are aged under 12 months, should complete the vaccination schedule (e.g., have 3 primary doses or 2 primary doses plus a booster).

When a first dose is given to a child older than 12 months of age, only 1 dose is recommended.

Hib vaccine is not required for healthy children after 5 years of age.

⁶For administration of pneumococcal conjugate vaccine (PCV) to infants, WHO recommends a 3-dose schedule administered either as 2p+1 or as 3p+0, starting as early as 6 weeks of age.

If the 2p+1 schedule is selected, an interval of ≥8 weeks is recommended between the 2 primary doses, and the booster dose should be given at 9–18 months of age, according to programmatic considerations; there is no defined minimum or maximum interval between the primary series and the booster dose.

If the 3p+0 schedule is used, a minimum interval of 4 weeks should be maintained between doses.

Interrupted schedules should be resumed without repeating the previous dose.

If a series cannot be completed with the same type of vaccine, the available PCV product should be used. Restarting a series is not recommended, even for the primary series.

Wherever possible, catch-up vaccination at the time of introduction of PCV should be used to accelerate its impact on disease in children aged 1–5 years, particularly in settings with a high disease burden and mortality. If there is limited availability of vaccine or of financial resources for catch-up vaccination, the youngest children (e.g., <2 years of age) should be prioritized to receive catch-up doses of PCV because of their higher risk for pneumococcal disease.

Catch-up vaccination can be done with a single dose of vaccine for children ≥24 months.

Unvaccinated children aged 1–5 years who are at high risk for pneumococcal infection because of underlying medical conditions, such as HIV infection or sickle-cell disease, should receive at least 2 doses separated by at least 8 weeks.

WHO does not currently have recommendations on the use of PCV in individuals over 5 years of age.

⁷Early immunization is favored with the first dose of rotavirus vaccine to be administered from 6 weeks of age; however, in order to benefit those who may come late, infants can receive doses without age restriction. Because of the typical age distribution of rotavirus gastroenteritis (RVGE), rotavirus vaccination of children >24 months of age is not recommended.

Regardless of the duration of delay, interrupted schedules should be resumed as soon as possible without repeating previous doses.

Rotavirus vaccinations can be administered simultaneously with other vaccines in the infant immunization program.

⁸For MenA conjugate vaccine (5μg) a 1-dose schedule is recommended in African countries at 9–18 months of age based on local programmatic and epidemiologic considerations.

There is no reason to expect interference when co-administered with other vaccines. The need for a booster dose has not been established.

If in a specific context there is a compelling reason to vaccinate infants younger than 9 months, a 2-dose schedule should be used starting at 2–3 months of age, with an interval of at least 8 weeks between doses.

For monovalent MenC conjugate vaccine one single intramuscular dose is recommended for children aged ≥12 months, teenagers, and adults. Children 2–11 months require 2 doses administered at an interval of a least 2 months and a booster about 1 year after.

If the primary series is interrupted, vaccination should be resumed without repeating the previous dose.

⁹A single dose of yellow fever (YF) vaccine is sufficient to confer sustained life-long protective immunity against YF disease; a booster dose is not necessary.

The vaccine is contraindicated in children aged <6 months and is not recommended for those aged 6–8 months, except during epidemics when the risk of infection with the YF virus is very high. Other contraindications for YF vaccination are severe hypersensitivity to egg antigens and severe immunodeficiency.

¹⁰Reaching all children with 2 doses of measles vaccine should be the standard for all national immunization programs. In addition to the first routine dose of MCV1, all countries should add a second routine dose of MCV2 to their national immunization schedules regardless of the level of MCV1 coverage.

Regardless of the duration of delay, interrupted schedules should be resumed as soon as possible without repeating previous doses.

Because many cases of measles occur in children aged >12 months who have not been vaccinated, routine delivery of MCV1 should not be limited to infants aged 9–12 months and routine delivery of MCV2 should not be limited to infants 15–18 months of age. Every opportunity (e.g., when children come into contact with health services) should be taken to vaccinate all children that missed one or both MCV routine doses, particularly those under 15 years of age. Policies that prohibit use of vaccine in children >1 year of age, older children, and teenagers should be changed to allow these individuals to be vaccinated. The minimum interval between MCV1 and MCV2 is 4 weeks.

¹¹Varicella vaccine can be administered concomitantly with other vaccines. Unless given together with other live viral vaccines (measles, MR, MMR), it should be administered at a minimum interval of 28 days.

Regardless of the duration of delay, interrupted schedules should be resumed as soon as possible without repeating previous doses.

¹²Inactivated hepatitis A (HAV) vaccine is licensed for intramuscular administration in a 2-dose schedule with the first dose given at the age of 1 year or older. The interval between the first and second dose is flexible (from 6 months up to 4–5 years) but is usually 6–18 months. Countries may consider a 1-dose schedule as this option seems comparable in terms of effectiveness and is less expensive and easier to implement. However, in individuals at substantial risk of contracting hepatitis A and in immunocompromised individuals, a 2-dose schedule is preferred. Inactivated HAV vaccines produced by different manufacturers, including combined hepatitis A vaccines, are interchangeable. Apart from severe allergic reaction to the previous dose, there is no contraindication to their use. These vaccines can be co-administered simultaneously with other routine childhood vaccines and should be considered for use in pregnant women at definite risk of HAV infection.

Source: Adapted by the authors, from: World Health Organization. Recommendations for Interrupted or Delayed Routine Immunization - Summary of WHO Position Papers [Table 3]. Geneva: WHO; 2023 [cited 31 January 2023]. Available from: https://www.who.int/teams/immunization-vaccines-and-biologicals/policies/who-recommendations-for-routine-immunization---summary-tables.