Booster effectiveness decreases after 4 months, but resists hospitalization

According to a study published Friday by the Centers for Disease Control and Prevention, booster shots of the Pfizer-BioNTech and Moderna vaccines lose substantial effectiveness after about four months – but still provided significant protection by preventing people from visiting. in the hospital during the omicron push.

Researchers found that booster shots remained highly effective against moderate and severe covid-19 for about two months after a third dose. But their effectiveness declined significantly after four months, suggesting the need for additional boosters, the study found.

The vaccine was 91% effective in preventing a vaccinated person from being hospitalized for two months following a booster shot, according to the study. But after four months, the protection dropped to 78%.

Protection waned further in preventing trips to urgent care and emergency departments, dropping from 87% in the first two months to 66% after four months. After more than five months, the vaccine’s effectiveness fell to around 31%, but the researchers noted that the estimate was “imprecise because little data was available” for this group of people.

Protection against the two-dose vaccine regimen has waned since omicron became dominant, but a third dose brings the immune system back to robust levels to prevent moderately severe and severe disease, an earlier CDC study found.

But how long the protection of this third vaccine lasts is a crucial question for public health officials, since many people received their third dose months ago. Decreased immunity after a third mRNA vaccine injection during omicron was observed in Israel and in preliminary CDC reports, according to the study. But Friday’s report represents the first real data in the United States on the durability of this protection during delta and omicron.

During a covid-19 briefing at the White House on Wednesday, Anthony Fauci, President Joe Biden’s chief medical adviser on the pandemic response, said officials would base recall decisions on “the actual effectiveness to prevent, for example, hospital visits, as well as hospitalizations”. “

“I think you should appreciate that when you’re talking about any decision that’s going to be made – and I’m not anticipating any of that right now – but it has to be put in the context of who you’re talking about,” he said. he declares.

“There may again be a need for another boost – in this case, a fourth dose boost for an individual receiving the mRNA – which could be based on age, as well as underlying conditions” , Fauci said.

Decreased protection after a third vaccine dose “reinforces the importance of considering more additional doses to maintain or improve protection against COVID-19-associated visits” in emergency departments and hospital care and hospitalizations. urgency, according to the study.

In a statement, the CDC said the boosters are “safe and effective” and the study shows that a third dose of mRNA vaccine “continues to provide high levels of protection against serious disease, even months later. administration, emphasizing the importance of staying current when eligible after receiving a first set.”

Since September, federal health officials have urged people to get vaccinated for the third time. The CDC recommends booster shots for anyone 12 and older, five months after receiving two doses of the mRNA vaccines made by Pfizer-BioNTech and Moderna, or two months after a single dose of the Johnson & Johnson vaccine.

About 91 million Americans have received reminders. Nearly 8 million people had received their reminders at least four months ago, according to CDC data. Most people eligible for the boosters did not receive them, according to the CDC’s calculations. This includes more than a third of the most vulnerable people aged 65 and over who received a full dose of regular vaccines but did not receive a booster.

Vermont, Minnesota, Wisconsin and Maine vaccinated the bulk of those previously vaccinated. The lowest rates for booster doses are in Alabama, Georgia, Texas, Mississippi and the District.

The CDC study looked at hospitalizations and visits to emergency rooms and urgent care centers in 10 states, from August to January 22, 2022, covering periods when delta and omicron were dominant. In the study, about 10% of people were boosted and more than 50% of those hospitalized were over 65 years old.

But the report did not assess variations in waning immunity based on age, underlying health conditions or a person’s immunocompromised status.

Experts said the results were not unexpected since studies have already shown that the effectiveness of the vaccine decreases after two doses.

Although the data suggests that additional boosters may be needed, the results underscore the added value of one booster over two doses. They also show that vaccines developed against ancestral viral strains still offer protection against newer variants, said Albert Ko, an infectious disease physician and epidemiologist at Yale’s School of Public Health.

Sara H. Byrd