The Pfizer and Moderna vaccines seemed too good to be true when they first arrived. The high efficacy rates of these two shots and their easily updated mRNA technology made them more attractive to some individuals than the Johnson & Johnson vaccine, which was less than 70 percent effective at preventing COVID cases from the jump. Pfizer also had the advantage of boasting less severe side effects than Moderna, on the whole. But while Pfizer might have been the early favorite for many people, new research has shown that its protective power may diminish faster than Moderna’s.
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On Oct. 4, The Lancet published a study that examined the Pfizer vaccine’s effectiveness over six months. According to the study, the effectiveness of Pfizer at preventing COVID infection dropped to 47 percent from 88 percent six months after the second dose. However, the vaccine’s effectiveness at preventing severe outcomes remained high. Pfizer was 90 percent effective at preventing hospitalization and death related to COVID for at least six months, even as the highly transmissible Delta variant became the most dominant strain of the virus.
The study asserted that the reduction in the vaccine’s effectiveness was primarily related to waning immunity over time, rather than the Delta variant evading the vaccine. Luis Jodar, MD, senior vice president and chief medical officer at Pfizer vaccines, told Reuters, “Our variant-specific analysis clearly shows that the vaccine is effective against all current variants of concern, including Delta.”
Vaccine effectiveness against the Delta variant began at 93 percent after the first month, then dropped to 54 percent after four months. Meanwhile, against other COVID strains, efficacy fell from 97 percent to 67 percent. “To us, that suggests Delta is not an escape variant that is completely evading vaccine protection,” study leader Sara Tartof, PhD, told Reuters.
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On Sept. 22, the U.S. Food and Drug Administration (FDA) authorized booster doses of the Pfizer vaccines for certain populations of people in the U.S. Those who are now eligible for a booster shot include people over 65 years of age, people at high risk for severe COVID, and people whose frequent exposure to COVID at work or an institution put them at high risk of severe COVID.
According to Reuters, U.S. health agencies consulted the data in the study when deciding whether or not Pfizer recipients needed a booster shot. On Oct. 14, the FDA will meet to discuss the question of booster shots for Moderna recipients.
However, since Moderna’s effectiveness doesn’t appear to wane as much as Pfizer’s, the vaccine company may not have as strong a case for booster doses. On Aug. 5, Moderna announced that its vaccine was still about 93 percent effective six months after the second dose, which is only a slight drop from its original reported efficacy of 94 percent during clinical trials.
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