Several popular vaccine opponents claim that the updated COVID-19 vaccines were not properly safety tested in humans, specifically emphasizing that Pfizer’s vaccine was tested in 10 mice and Moderna’s in 50 people.
This misleading claim underscores a persistent misconception about how vaccines are developed and tested. Debunking messaging may explain that updated COVID-19 vaccines use the same basic formula as the original vaccine and don’t require extensive testing, similar to annual flu shots and other vaccines that are updated to protect against multiple strains of the same pathogen. COVID-19 vaccine ingredients have been safety tested and monitored for over three years. Minor changes to the vaccine’s targets, like those in the updated COVID-19 vaccines, don’t impact its safety. Messaging may also emphasize that updated COVID-19 vaccines are effective against the XBB.1.5 subvariant and its close relatives, which make up around 90 percent of circulating variants.
