In 2013, the World Health Organization (WHO) released guidance that a single lifetime yellow fever shot was sufficient for most people. Previous guidance had recommended a booster every 10 years for those traveling or living in areas where the yellow fever is endemic. The evidence they gave is the fact that virtually all documented instances of someone acquiring the disease after vaccination occurred in the first five years after vaccination, indicating that the efficacy did not drop off over time. If it did, most breakthrough cases would be 10 or 20 years or more after infection. We wrote a recent blog post discussing the CDC guidance but in this post we'll evaluate the most current research more directly.
A team of epidemiologists studying the disease recently looked at how long the yellow fever vaccine lasts in order to assess whether it truly does confer lifelong immunity (Domingo et al. 2022). The team of researchers conducted a "meta-analysis," a study that aggregates data together from all available studies in an area. In total they included 36 prior studies in their analysis. These studies had different sample populations, methodological approaches and research teams.
What they found is that immunity does start to drop off after 10 years or so but it remains high. In the average adult, yellow fever immunity goes from 98% effective within the first three months to 86% effective between 10 and 20 years after receiving the yellow fever vaccine.
In immunocompromised adults, protection is 92% but drops to 62% in the 10 to 20 year post-vaccination period. This indicates that immunocompromised individuals should get a yellow fever booster if they live in yellow fever endemic areas (or are visiting them for extended periods) and don't have contraindications.
Another interesting thing is that no studies have been run that have looked at healthy adults more than 20 years after receiving the yellow fever vaccine. There is also a general lack of information about yellow fever booster shots. Few studies have been run on the topic. Another problem is that it is difficult to monitor the actual number of vaccine breakthroughs because of a lack of record-keeping and reporting in areas where the yellow fever virus is endemic.
Reference
Kling, K., Domingo, C., Bogdan, C., Duffy, S., Harder, T., Howick, J., ... & Wolff, R. (2022). Duration of Protection After Vaccination Against Yellow Fever: A Systematic Review and Meta-Analysis. Clinical infectious diseases, 75(12), 2266-2274.