Fever is a necessary and adaptive part of our immune response. We generate fever after infection, and sometimes after vaccination, to promote better immune responses. This phenomenon was demonstrated by a recent study in Australia that validated a previous study done in the Czech Republic.

On Feb. 19, 2018, researchers in Australia published the results of three pooled studies involving 3,317 children who had received an influenza vaccine to determine whether acetaminophen (Tylenol®) influenced immune responses (Li-Kim-Moy J, Wood N, Jones C, et al. Impact of Fever and Antipyretic Use on Influenza Vaccine Immune Responses in Children. Pediatr Infect Dis J. 2018 Feb 19, doi:10.1097/INF.0000000000001949). They found that children with post-vaccination fever had significantly higher adjusted geometric mean titers (GMTs) than those without fever. Conversely, children who were treated with antipyretics at or soon after vaccination had significantly lower GMTs than those who weren’t treated. The authors concluded that “fever and antipyretic use may have important associations with influenza vaccine immunogenicity.”

Similarly, in 2009, researchers in the Czech Republic divided 459 children who were about to receive vaccines into two groups: one group received acetaminophen every six to eight hours for 24 hours, the other didn’t (Prymula R, Siegrist CA, Chilbek R, et al. Effect of Prophylactic Paracetamol Administration at Time of Vaccination on Febrile Reactions and Antibody Responses in Children: Two Open-Label, Randomised Controlled Trials. Lancet 2009;Oct 17;374:1339-50). Investigators found a significant decrease in antibody responses against tetanus toxoid, diphtheria toxoid, the pertactin component of the pertussis vaccine, all 10 pneumococcal serotypes, and the antipolyribosyl-ribitol phosphate component of the Haemophilus influenzae type b (Hib) vaccine. These lowered immune responses persisted even after booster dosing. The authors concluded that, “prophylactic administration of antipyretic drugs at the time of vaccination should not be routinely recommended.”

Taken together, these studies support avoidance of antipyretics around the time of vaccination.

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

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