CDC scientist says there's limited data to evaluate Covid booster doses for general population

A new CDC presentation says the data needed to properly evaluate Covid-19 vaccine booster shots for the general population is limited — even as U.S. President Joe Biden pressures health officials to clear the shots for wide distribution beginning the week of Sept. 20.

Slides published ahead of a presentation at a Centers for Disease Control and Prevention advisory group meeting Monday suggest the panel may limit its initial endorsement of extra shots to vulnerable groups and health-care workers.

Several studies suggest the authorized Covid vaccines remain effective in preventing severe disease and hospitalization but may be less effective in preventing infection or mild symptomatic illness, according to the slides submitted by CDC scientist Dr. Sara Oliver. The CDC's Advisory Committee on Immunization Practices is meeting Monday to consider booster shots for all eligible Americans. They are also scheduled to vote on endorsing the Food and Drug Administration's final approval of Pfizer's vaccine.

Since the highly contagious delta variant first appeared, vaccine efficacy has ranged between 39% and 84%, according to the presentation, which referenced several separate studies. One study looking at health-care workers and first responders showed overall vaccine efficacy fell to around 65% in July – down from about 90% in February, according to the slides. Israel data shows the efficacy of Pfizer's vaccine has fallen to as low as 39% in that country.

Scientists have said the vaccines' effectiveness wanes over time, and the delta variant is a hardier strain that is able to break through that protection.

It is "important to monitor trends of effectiveness by severity of disease over time," the slides said.

The slides noted that it is not uncommon for vaccines to require several doses. Vaccinations for Hepatitis B and HPV, for example, require a third dose after six months.

Once booster shots are available, nursing home residents, health-care providers and the elderly — the first groups to get vaccinated in December and January — are likely to be prioritized for the extra shots, the CDC slides suggested.

The CDC emphasized that vaccinating the unvaccinated should be a "top priority," adding delivery of booster doses to vaccinated individuals should not deter outreach to those who remain unprotected from the virus.

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The agency also stressed the importance of the availability of vaccines globally.

"Uncontrolled spread globally that could result in new variants threaten control of the pandemic everywhere," one slide said.

The meeting Monday comes after President Joe Biden said Friday that U.S. regulators are looking at administering Covid booster shots five months after people finish their primary immunizations, moving up the expected timetable for a third shot by three months.

Scientists have sharply criticized the Biden administration's push to widely distribute booster shots, saying data provided by federal health officials isn't compelling enough to recommend third shots to most of the American population right now.

The Biden Administration has publicly said that third doses will not go ahead without FDA approval and a vote by ACIP.

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