The effectiveness of post-exposure vaccination for protection against infectious disease was explored in a recently published review in the journal Epidemiologic Reviews

While the effectiveness of pre-exposure vaccination is well known, there appears to be greater uncertainty surrounding the use of vaccines to modify or prevent a disease after exposure. To summarize the evidence surrounding this topic, study authors searched PubMed to obtain clinical trials and observational studies evaluating  post-exposure vaccination effects. “Eligible studies were evaluated by definition of exposure, and their attempt at distinguishing pre- and post-exposure effects was rated on a scale of 1-4,” the authors explained. 

Of the 4518 articles screened, a total of 45 studies (14 clinical trials and 31 observational studies) were considered eligible and included in the review. Results of the analysis revealed that the strength of post-exposure vaccination effectiveness against secondary attack varied across diseases. Medians for post-exposure effectiveness were reported as the following: 85% for hepatitis A, 85% for hepatitis B, 83% for measles, 67% for varicella, 45% for smallpox, and 38% for mumps. In addition, a review of studies evaluating vaccine effectiveness against fatality showed median efficacies of 100% for rabies vaccine and 63% for smallpox vaccine.

Findings of this review demonstrated that there is a lack of knowledge regarding post-exposure effectiveness of many common vaccines and highlighted the importance of researching this area further. “As evidenced by this report, post-exposure effectiveness has not been fully explored even for common vaccines, and there are several scenarios in which they are important: responding to unpredictable health emergencies, designing new treatments, and interpreting vaccine trials,” the authors concluded. They added, “Therefore, post-exposure effects not only concern innovative treatments for exposed or infected individuals, but could also improve how we anticipate and understand the impact of any vaccine.”

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