As the delta variant became the dominant coronavirus strain in the United States, all three COVID-19 vaccines available to Americans have lost some of their defenses, and vaccine efficacy among a large group of veterans has dropped from 35% to 85%, according to a new study.
Researchers looking at the records of nearly 800,000 U.S. veterans found that in early March, when the delta variant took off in American communities, the three vaccines were roughly equal in their ability to prevent infections.
But over the next six months, everything changed dramatically.
By the end of September, Moderna’s two-dose COVID-19 vaccine, which was 89% effective in March, was only 58% effective.
The effectiveness of the Pfizer vaccine, which also uses two doses, fell from 87% to 45% over the same period.
Most strikingly, the protective power of Johnson & Johnson’s single-shot vaccine fell from 86% to just 13% in those six months.
The results were published Thursday in the journal Science.
The three vaccines were superior in their ability to prevent death from COVID-19, but by July, when the delta variant began to cause a three-month spike in infections and deaths, vaccine efficacy in this indicator also revealed large gaps.
Among veterans 65 and older who received the Moderna vaccine, those who develop a breakthrough infection are 76% less likely to die from COVID-19 than unvaccinated veterans of the same age.
Older veterans who received the Pfizer vaccine and subsequently suffered a breakthrough infection were 70% less likely to die than their unvaccinated peers.
And when older veterinarians who received one shot of J&J vaccine suffered a breakthrough infection, they were 52% less likely to die than their peers who had not received any vaccines.
For veterans under 65, the Pfizer and Moderna vaccines provided the best protection against COVID-19 fatalities – 84% and 82%, respectively. When young veterans vaccinated with the J&J vaccine suffer a breakthrough infection, they are 73% less likely to die from COVID-19 than their unvaccinated peers.
Johnson & Johnson did not immediately respond to requests for discussion of the study’s findings.
The Centers for Disease Control and Prevention recommended booster vaccinations for anyone who received the Johnson & Johnson vaccine at least two months earlier.
Boosters are also recommended six months after the second dose of Moderna or Pfizer vaccines for all people over 65; people with medical conditions that make them more vulnerable to a serious case of COVID-19; those who live in nursing homes or other groups; and those who live or work in high-risk settings such as hospitals or prisons.
In addition, booster vaccinations are recommended for all people with weakened immune systems if at least 28 days have passed since the vaccine was fully effective.
Millions of vaccinated Americans are considering whether they need boosted vaccinations, and a new study offers the most comprehensive comparison of the effectiveness of these three vaccines nationwide this year.
From February 1 to October 1, it tracked 780,225 veterans of the US military. About 500,000 of them were vaccinated, and just under 300,000 were not.
Coming from all over the country, everyone was under the care of a unified veterans affairs system, which provides medical care to 2.7% of the US population. Although the study group was ethnically and racially diverse, the accounting on which the researchers relied was uniform.
Since they were veterans, the study population included six times as many males as females. And they turned out to be older: about 48% were 65 or older, 29% were between 50 and 64, and 24% were under 50.
While older veterans were more susceptible to death than younger veterans throughout the study period, decreased vaccine protection against disease and death was observed in both young and old.
The study was conducted by a team from the Institute of Public Health in Oakland, California, the Veterans Affairs Medical Center in San Francisco, and the University of Texas Health Science Center.
Dr. Barbara Cohn, lead author of the study, said that in addition to comparing COVID-19 vaccines, the group’s analysis provides “the lens for making informed decisions about primary vaccinations, revaccinations and other multiple layers of protection.” This includes requirements for masks, coronavirus testing, and other public health measures to counter the spread of the virus.
Strong evidence of declining vaccine efficacy should prompt even states and regions with highly vaccinated populations to consider maintaining mask mandates, the authors say. And the findings strongly support the CDC’s recent recommendation that all J&J recipients receive booster vaccinations.
The study concluded that the delta variant, which caused a wave of infections and deaths across the country this spring and summer, was likely the factor that most undermined vaccine protection.
Other researchers have found similar evidence of reduced vaccine efficacy. But they suggested that the immune system’s defense against SARS-CoV-2 simply wanes over time, and that the decline in vaccine effectiveness would likely be seen with or without a new, more transmissible strain.