Infants under 9 months of age
The risk of yellow fever vaccine-associated encephalitis is higher in infants under nine months of age
Image provided by NHS Photo Library
The risk of yellow fever (YF) vaccine-associated encephalitis is higher in infants under nine months of age [1]. The risk is inversely proportional to age (highest risk for the youngest infants) [1-3]. During the 1950s, when there was no age restriction on the use of the YF vaccine, 15 cases of encephalitis were reported in infants. Of the 15 cases, 13 (87%) occurred in infants under four months of age and all were under seven months of age (age was not documented in the remaining two cases) [2]. The vaccine should therefore never be administered to infants under six months of age [1, 2].
Infants aged six to nine months should only be immunised if the risk of YF during travel is unavoidable; expert opinion should be sought in these situations [1]. For this age group, vaccination is usually only recommended during epidemics/outbreaks when the risk of YF virus transmission may be very high [see TravelHealthPro Country Information pages].
Individual itineraries should be considered on a case-by-case basis, and if possible, travel should be delayed until the infant is 9 months of age [2].
When travel is unavoidable, and YF vaccine is not an option, particular care with insect bite avoidance day and night should be recommended.
Very young children (aged less than 2 years) are recommended to have a reinforcing dose once the child is 2 years or older, depending on the next planned travel to an area of risk. This is due to waning seroprotection, which may occur 3 months to 5 years following primary vaccination in some children who are vaccinated under 2 years of age [1, 4-5].
References
-
UK Health Security Agency. Yellow Fever. Ch 35. In: Immunisation against infectious disease. March 2024 [Accessed 23 August 2024]
-
Plotkin, S.A. Orenstein, W.A and Offit, P.A Yellow fever vaccine, Ch 38 in Vaccines 6th edition, 2013, Elsevier Saunders, pg 947.
-
World Health Organization, Vaccines and vaccination against yellow fever WHO Position Paper - June 2013, weekly epidemiological record, 5 July 2013
-
SAGE Working Group, Background Paper on Yellow Fever Vaccine 19 March 2013
-
Kling K, Domingo C, Bogdan C, et al. Duration of Protection after Vaccination against Yellow Fever: A Systematic Review and Meta-Analysis. CID. 2022: 75 (12)