Studies Show COVID Boosters Remain Effective for Months

FRIDAY, Feb. 11, 2022 (HealthDay News) -- The power of COVID booster shots do wane somewhat over four months, but they still continue to provide high levels of protection against severe disease, a new government study has found.

Booster effectiveness against hospitalization during the Omicron surge was 91% during the first two months after a third dose, researchers from the U.S. Centers for Disease Control and Prevention reported.

What's more, protection against symptoms severe enough to land you in the hospital remained high, at 78%, four or more months after a booster dose, they discovered.

For this study, CDC examined data on 93,000 hospitalizations and 241,000 emergency department and urgent care visits across 10 states during the Delta and Omicron waves. In the study, about 10% of people were boosted and over 50% of people hospitalized were over 65.

Experts were not surprised by the findings since the same thing happened with the first two doses, and stressed that folks need not panic.

While the data suggest that additional boosters may be needed, the findings underscore the added value of a booster.

"Each time we are boosting with these vaccines, our immune responses may be getting broader and not narrower in protecting against the scope of variants we are encountering," Dr. Albert Ko, an infectious-diseases physician and epidemiologist at Yale's School of Public Health, told the Washington Post. Protection against the array of variants two years into the pandemic is "pretty amazing, whether you're getting the primary series or that boost."

Even after four months, the 78% effectiveness in preventing hospitalizations is "...another argument that getting boosted now will prepare you better when you need to get boosted again in the face of new variants," Ko added.

While a booster's protection declines more over time in preventing visits to urgent care or emergency departments, Dr. Jeanne Marrazzo, an infectious-diseases physician at the University of Alabama at Birmingham, also noted the robust protection against hospitalization, even after four months.

The study does not provide the level of detail to know whether people were going to urgent care clinics for "a little sniffle," she told the Post. "That's not the same thing as coming into the ICU and needing to be intubated."

"I honestly think we were unrealistic early on in conveying the idea that vaccine efficacy should be primarily characterized by protecting from infection," Marrazzo said. "As variants evolve and get better at infecting us, what we'll need to focus on is mitigating the consequences."

A second study in the Feb. 11 issue of the CDC publication Morbidity and Mortality Weekly Report found that booster shots are safe overall, and tend to produce fewer side effects if you get a third dose of the same mRNA vaccine as your initial series.

For that report, the CDC reviewed data from two of its vaccine safety monitoring systems, v-safe and the Vaccine Adverse Event Reporting System (VAERS).

The investigators found that people 18 and older who received the same mRNA vaccine brand for all their vaccinations actually experienced fewer adverse reactions following the booster dose than they did after their second dose.

About 92% of reports to VAERS were not considered serious, and headache, fever, and muscle pain were among the most commonly reported reactions. V-safe data found medical care was rarely needed after a booster dose.

About 91 million Americans have received boosters. Nearly 8 million had gotten their boosters at least four months ago, according to CDC data.

More information

Visit the U.S. Centers for Disease Control and Prevention for more on COVID boosters.

SOURCES: U.S. Centers for Disease Control and Prevention, news release, Feb. 11, 2022; Washington Post