Covid-19 vaccine effectiveness against severe disease has not dropped much, CDC says

Overall effectiveness of coronavirus vaccines has not dropped much yet for most vaccinated Americans, US Centers for Disease Control and Prevention vaccine advisers were told Monday.

Posted 1:28 a.m. Aug 31, 2021 — Updated 1:28 a.m. Aug 31, 2021

Maggie Fox

, CNN

CNN — Overall effectiveness of coronavirus vaccines has not dropped much yet for most vaccinated Americans, US Centers for Disease Control and Prevention vaccine advisers were told Monday.

CDC's Advisory Committee on Immunization Practices met Monday to discuss the potential eventual need for booster doses of coronavirus vaccine -- although they did not vote. The White House has said it's planning to offer booster doses at the end of September, although it's up to the US Food and Drug Administration and the CDC to decide on this.

So far, in data that goes through July, the vaccines still appear to provide strong protection, the CDC's Dr. Sara Oliver told ACIP Monday.

"Since the introduction of the Delta variant, VE against infection ranges from 39 to 84%. VE against hospitalization, though, remains high from 75% to 95%," Oliver said, citing global data.

"Regardless of the vaccine evaluated, all vaccines remain effective in preventing hospitalization and severe disease. But they may be less effective in preventing infection and mild illness recently," Oliver added. "These reasons for lower effectiveness likely include both waning over time and the Delta variant."

One US study showed vaccine effectiveness against hospitalization in adults 65 and older may have decreased, but only slightly, over time, she said. Unpublished CDC data shows vaccine effectiveness remains very high, at 94% or higher in adults 18 to 74, she said.

"Preliminary VE against hospitalization in adults 75 years of age and older ... decreased in July but still remained over 80%," Oliver said.

Vaccine efficacy has fallen from 75% at first to just over 50% among long term care facility residents, Oliver said. These were the first people vaccinated after the shots became available in December and January.

"The data we have seen today has demonstrated that Covid vaccines continue to maintain high protection against severe disease, hospitalization and death. Protection against infection, including asymptomatic and mild infection, appears to be lower in recent months," she said.

All three companies making vaccines for the US market -- Pfizer/BioNTech, Moderna and Johnson & Johnson -- are evaluating the effects of booster doses, she said.

The major questions are whether booster doses are safe and work to improve protection, she said.

"Will booster doses of Covid-19 vaccines reduce Covid-19 incidence, hospitalization and/or mortality?" she asked.

ACIP will meet in the coming weeks to discuss data about vaccine efficacy in August, Oliver said. "We will announce meetings as soon as we have dates," the CDC's Dr. Amanda Cohn said at the end of Monday's meeting.

The CDC and FDA endorsed the use of boosters in certain immunocompromised people earlier this month. While the White House has pressed for booster doses to be offered more widely, the CDC and FDA are waiting for more information from the companies.

But White House officials say they're looking at data from Israel as well as from the US, and want to be sure to be ahead of any changes in the pandemic.

On Monday, Israel started offering a booster to everyone 12 and older who had been vaccinated at least five months ago.

Researchers in Israel reported Monday that people who chose to get a third dose of vaccine had a much lower risk of becoming infected, even as the more transmissible Delta variant swept across the country.

"Conclusions: In conjunction with safety reports, this study demonstrates the effectiveness of a third vaccine dose in both reducing transmission and severe disease and indicates the great potential of curtailing the Delta variant resurgence by administering booster shots," Yair Goldberg of the Technion-Israel Institute of Technology and colleagues wrote in their report, posted online by the Israeli government.

The researchers noted that it is difficult to account for differences among people in a real-world study. People who choose to get a booster dose may be different from those who choose not to, and people behave differently after they've received a shot.

One major difference: recently vaccinated people are less likely to be tested for coronavirus infection, which means fewer infections would be detected in that group. Recently vaccinated people may also take more care to prevent infection.

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