When the Delta variant became the dominant strain of the coronavirus in the United States, all three COVID-19 vaccines available to Americans lost some of their protective power, with the vaccine’s efficacy declining in a large group of veterans. between 35% and 85%, according to a new study.
Researchers who searched the records of nearly 800,000 U.S. veterans found that in early March, just as the Delta variant was taking hold in U.S. communities, the three vaccines were roughly equal in their ability to prevent infection.
But that changed drastically over the next six months.
By the end of September, Moderna’s two-dose COVID-19 vaccine, measured as 89% effective in March, was only 58% effective.
The effectiveness of shots made by Pfizer and BioNTech vaccine, which also used two doses, fell from 87% to 45% over the same period.
And most notably, the protective power of Johnson & Johnson’s single-use vaccine dropped from 86% to just 13% in those six months.
The findings were published Thursday in the journal Science.
The three vaccines held up better in their ability to prevent COVID-19 deaths, but by July — when the Delta variant started causing a three-month spate of infections and deaths — the shots’ effectiveness at that point also revealed. big gaps.
Among veterans 65 and older who were vaccinated with the Moderna vaccine, those who developed a “breakthrough” infection were 76% less likely to die from COVID-19 compared to unvaccinated veterans of the same age.
Older veterans who received the Pfizer-BioNTech vaccine and subsequently experienced a breakthrough infection were 70% less likely to die than their unvaccinated peers.
And when older vets who received a single injection of the J&J vaccine developed a breakthrough infection, they were 52% less likely to die than their peers who did not receive the injections.
For veterans under the age of 65, the Pfizer-BioNTech and Moderna vaccines provided the best protection against a fatal case of COVID-19, at 84% and 82%, respectively. When younger veterans vaccinated with the J&J vaccine developed a breakthrough infection, they were 73% less likely to die from COVID-19 than their unvaccinated peers.
Representatives of Johnson & Johnson did not immediately respond to requests to discuss the findings of the investigation.
The Centers for Disease Control and Prevention has recommended booster shots for anyone who has received the Johnson & Johnson vaccine at least two months before.
Boosters are also recommended six months after a second dose of the Moderna or Pfizer vaccines for anyone 65 and older; people with medical conditions that make them more vulnerable to a severe case of COVID-19; those who live in nursing homes or other group settings; and those who live or work in high-risk environments such as hospitals or prisons.
In addition, all people with compromised immune systems are advised to receive a booster shot if it has been at least 28 days since their vaccine has taken full effect.
With millions of unvaccinated Americans pondering whether they need a boost, the new study offers the most comprehensive comparison yet of how the three vaccines have performed across the country this year.
It tracked 780,225 veterans of the United States Armed Forces from February 1 to October 1. Nearly 500,000 of them had been vaccinated, while just under 300,000 had not.
They came from all over the country and were all cared for by the unified system of Veterans Affairs, which provides health care to 2.7% of the U.S. population. Although the group studied was ethnically and racially diverse, the administration researchers relied on was uniform.
Because these were veterans, the study population consisted of six times as many men as women. And they were older: About 48% were 65 or older, 29% were between 50 and 64, and 24% were under 50.
While older veterans were more likely to die than younger vets during the study period, the decline in vaccine protection against illness and death was seen in both young and old.
The study was conducted by a team from the Public Health Institute in Oakland, the Veterans Affairs Medical Center in San Francisco and the University of Texas Health Science Center.
dr. Barbara Cohn, the study’s lead author, said that in addition to comparing COVID-19 vaccines, the group’s analysis “provides a lens for making informed decisions about primary vaccination, booster shots, and other multiple layers of protection.” That includes mask mandates, coronavirus testing and other public health measures aimed at curbing viral spread.
Strong evidence of the vaccine’s declining potency should prompt even states and places with highly vaccinated populations to consider retaining mask mandates, the authors said. And the findings strongly support the CDC’s recent recommendation that all recipients of the J&J vaccine receive a booster.
The study concluded that the Delta variant, which caused a spate of infections and deaths across the country this spring and summer, was likely the factor most affecting vaccine protection.
Other researchers have found similar evidence of declining vaccine effectiveness. But they have suggested that the immune system’s defenses against SARS-CoV-2 simply fade over time, and that the vaccine’s declining effectiveness would likely have been observed with or without the advent of a new, more transmissible strain.
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