The effectiveness of COVID-19 vaccines produced by Pfizer/BioNTech, Moderna, and Johnson & Johnson dropped dramatically as the Delta variant swept the United States, a study of almost 800,000 veterans found.
The study, published in the journal Science, says the three vaccines offered about the same protection against the virus in March, when the Delta variant was first detected in the U.S., but that changed 6 months later.
Meanwhile, the Pfizer/BioNTech vaccine went from being 87% effective to 45% effective over the same time period.
The Johnson & Johnson vaccine showed the biggest drop — from 86% effectiveness to 13% over those 6 months.
“In summary, although vaccination remains protective against SARS-CoV-2 infection, protection waned as the Delta variant emerged in the U.S., and this decline did not differ by age,” the study said.
The three vaccines also lost effectiveness in the ability to protect against death in veterans 65 and over after only 3 months, the Los Angeles Times reported.
Compared to unvaccinated veterans in that age group, veterans who got the Moderna vaccine and had a breakthrough case were 76% less likely to die of COVID-19 by July.
The protection was 70% for Pfizer/BioNTech vaccine recipients and 52% for J&J vaccine recipients for the same age group, compared to unvaccinated veterans, according to the newspaper.
For veterans under 65, the protectiveness against a fatal case of COVID was 84% for Pfizer/BioNTech recipients, 82% for Moderna recipients, and 73% for J&J recipients, compared to unvaccinated veterans in that age group.
Of the veterans studied, about 500,000 were vaccinated and 300,000 were not. Researchers noted that the study population had 6 times as many men as women. About 48% of the study group was 65 or older, 29% was 50-64, while 24% was under 50.
Researchers from the Public Health Institute in Oakland, CA, the Veterans Affairs Medical Center in San Francisco, and the University of Texas Health Science Center conducted the study.