Yellow fever vaccine and risk of developing serious adverse events: a systematic review

Objective. To evaluate contraindications and precautions for the yellow fever vaccine (YFV) in risk populations. Methods. A literature review was conducted by searching PubMed for "yellow fever vaccine" and "adverse events" (AEs); 207 studies were found, and 43 of them met the inclusion criteria and were included in a systematic review. Results. The results for first dose of YFV in elderly patients were conflicting-some showed AEs while some showed benefits. Therefore, precaution and case-by-case decision-making for YFV in this population are advised. The same precautions are warranted for YFV in infants 6-8 months, with the vaccine contraindicated in those < 6 months old and safe after 9 months of age. YFV seems safe in the first trimester of pregnancy, and probably throughout gestation, as it was not associated with increased malformations. During breast-feeding, YFV continues to be controversial. The vaccine seems safe in people being treated with immunomodulatory or immunosuppressive therapy, people with immunosuppressive diseases, and solid organ and hematopoietic stem cell transplant patients; in stem cell transplants, however, a booster dose should only be applied once immunity is recovered. HIV-infected patients with a CD4+ count > 200 cells/mm(3) do not have increased risk of AEs from YFV. Egg allergy vaccination protocols seem to provide a safe way to immunize these patients. Conclusions. YFV safety has been confirmed based on data from many vaccination campaigns and multiple studies. AEs seem more frequent after a first-time dose, mainly in risk groups, but this review evaluated YFV in several of the same risk groups and the vaccine was found to be safe in most of them.