Wednesday, September 27, 2023

Will a first-dose vaccination strategy help overcome variants?

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In a report published on February 23, Osterholm and colleagues calculate that temporarily prioritizing first doses for people over 65 could save up to 39,000 lives. “There is a narrow and quickly closing window of opportunity to use vaccines more effectively and potentially prevent thousands of serious cases, hospitalizations and deaths in the weeks and months to come,” the authors write.

The UK adopted a similar strategy in December and Quebec announced in January that it would stop withholding booster shots and try to vaccinate as many people as possible, delaying the second vaccine for up to 90 days.

But many public health experts, including senior advisers to the Biden administration, say there is not enough data to support the move to a single-dose strategy. They fear that postponing the second dose will leave people vulnerable to infection and potentially give rise to new variants that may elude the immune response. And there is logistics to consider. Changing strategy would now complicate deployment, says Celine Gounder, an epidemiologist at the NYU Grossman School of Medicine and a member of the Biden administration’s covid-19 advisory committee. “We really have to break the current system, which is already very fragile,” she said. It could also hurt the already weak public confidence in the vaccine.

“Based on the information currently available to us, we will stick to the scientifically documented efficacy and optimal response of a first follow-up boost,” said Anthony Fauci, Chief Medical Advisor to President Biden , during a press briefing on February 19. Andy Slavitt, The White House’s Senior Advisor on COVID-19 Response, agreed. “The FDA recommendation is two doses, as has always been the case,” he said.

The big question of protection

The debate revolves around the degree of protection offered by a dose and the duration of that protection.

In large clinical trials, Moderna and Pfizer have seen good efficacy even before the second shot. The first dose of the Pfizer vaccine provided 52% protection against symptomatic covid-19 and the Moderna vaccine achieved 80% efficacy. But those numbers included the days immediately after vaccination, when the immune system further accelerates its response. When the researchers looked at the effectiveness two weeks after the date of the shot, they found much higher numbers. Analysis suggests the Pfizer vaccine was nearly 92% effective before the second injection. The first dose of Moderna was 92% effective after two weeks.

And new research suggests that a dose might offer some protection in a real world setting as well. In a new study in the New England Journal of Medicine, the researchers examined the medical records of nearly 600,000 people vaccinated in Israel and the same number of witnesses. The first dose of Pfizer vaccine was 46% effective against SARS-CoV-2 infection between days 14 and 20. The vaccine did a better job of preventing hospitalization and death: protecting was 74% and 72%, respectively.


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