Comprehensive study finds vaccines remarkably safe

The most common safety issue that resulted in label changes for vaccines was a restriction on the population to be vaccinated, such as pregnant or immunocompromised patients.

A comprehensive review of vaccine postmarket surveillance data over a 20-year period found that vaccines are remarkably safe, a large proportion of safety issues were identified through surveillance programs, and any adverse events were of limited clinical significance.

Researchers studied initial and subsequent labels of 57 vaccines approved by the FDA between January 1996 and December 2015 to explore postmarketing safety modifications. Researchers aggregated hundreds of thousands of reports from the FDA's Vaccine Adverse Event Reporting System (VAERS), following hundreds of millions of administered vaccines.

For each vaccine, they compared the most recent label with the initial label and with all available subsequent labels for any safety-related changes. For each safety-related modification, researchers identified date of label change, type of safety-related label change (addition of a boxed warning, change in contraindications, or change in warnings and precautions), clinical safety issue related to the label change, and source of data leading to the label change (postmarketing surveillance, publication in medical literature, reassessment of existing study data, or other sources). Results were published July 28 by Annals of Internal Medicine.

Initial approval for 53 (93%) of the 57 studied vaccines was supported by randomized controlled trials, with a median cohort size of 4,161 participants (interquartile range, 2,204 to 8,634 participants). There were 58 postapproval, safety-related label modifications associated with 25 vaccines (49 warnings and precautions, eight contraindications, and one safety-related withdrawal).

The most common safety issue triggering label modifications was a change in the population to be vaccinated, such as pregnant or immunocompromised patients (n=21; 36%), followed by allergies (n=13; 22%), mostly due to changes in latex-containing packaging. The most common source of safety data was postmarketing surveillance (n=28; 48%). Most new safety data were identified through the VAERS, which authors attributed to the quality of the FDA's postmarketing surveillance of vaccine side effects.

According to the researchers, these findings show that vaccines are safe and that public vaccination should remain a major public health strategy. “Vaccine safety and public trust in vaccine safety are central public health issues,” they wrote. “Rates of vaccination uptake have been decreasing in recent years, partly driven by reduced public trust and parental concerns over safety. If vaccines are perceived as unsafe, uptake in the population will decrease further, and the prevalence of infectious diseases and their associated morbidity and mortality will increase.”