Officials changed their guidance after three studies showed that the delta variant led to waning protection from the COVID-19 vaccines, though they still prevented severe illness

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A healthcare Worker hands in surgical gloves pulling COVID-19 vaccine liquid from vial to vaccinate a patient
Vaccine
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The Biden administration announced Wednesday that vaccinated Americans should receive a COVID-19 booster shot eight months after being fully inoculated due to waning immunity.

Top health officials said in a press conference that eligible people who received the Pfizer or Moderna vaccines will start getting their third dose beginning Sept. 20.

The shift in guidance was based on three new studies that indicated the need for a booster to protect against the more aggressive delta variant that has quickly become dominant in the U.S. 

Officials also expect that Americans who received one dose of the Johnson & Johnson vaccine will need an additional shot, pending results of a two-dose clinical trial that will be available later this month before any official announcements are made.

"The available data make very clear that protection against SARS-CoV-2 infection begins to decrease over time following the initial doses of vaccination, and in association with the dominance of the delta variant, we are starting to see evidence of reduced protection against mild and moderate disease," the CDC said in a statement.

Much like the initial vaccine rollout in December 2020, nursing home residents, health care workers and emergency workers are expected to receive the third booster shot first. Next up would be older recipients, then the general U.S. population. People are expected to receive a third shot of the same vaccine they originally got. 

The expected booster announcement comes as the U.S sees a summertime spike in COVID-19 cases after a promising dip in late spring. But with the highly contagious delta variant circulating and large portions of the country declining to get vaccinated, cases have soared back to levels last seen in January, before the vaccines were widely available to the public.

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COVID-19 vaccine
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The FDA and CDC initially said Americans did not need a booster shot in a joint statement in July.  

"People who are fully vaccinated are protected from severe disease and death, including from the variants currently circulating in the country such as delta," the agencies said at the time. "People who are not vaccinated remain at risk. Virtually all COVID-19 hospitalizations and deaths are among those who are unvaccinated." 

The FDA and CDC also stressed that they were working with the NIH on a "science-based, rigorous process to consider whether or when a booster might be necessary." 

While the U.S. will begin to administer shots next month, the World Health Organization argued in early August that countries with reduced access to the COVID-19 vaccine should be able to vaccinate their populations before other countries begin to roll out a booster shot program. 

The WHO called for a moratorium on booster shots until the end of September, with director-general Tedros Adhanom Ghebreyesus asking the world's "wealthiest countries" to pause their plans for additional vaccinations. 

"I understand the concern of all governments to protect their people from the Delta variant," Ghebreyesus said at the time. "But we cannot — and we should not — accept countries that have already used most of the global supply of vaccines using even more of it, while the world's most vulnerable people remain unprotected."

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