Lifestyle Health Biden Administration Says Vaccinated Americans Will Start Getting COVID Booster Shots Sept. 20 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 By Greta Bjornson Greta Bjornson Twitter Digital News Writer, PEOPLE People Editorial Guidelines Updated on August 18, 2021 12:04 PM Share Tweet Pin Email Vaccine. Photo: Getty 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. Children Hospitalized for COVID Hit Record High in the U.S. This Weekend, per HHS Data 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. COVID-19 vaccine. Chip Somodevilla/Getty Joe Biden Addresses Viral Tennessee Mask Protest Video: 'Our Healthcare Workers Are Heroes' 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. German Nurse Suspected of Giving Thousands Saline Solution Instead of COVID Vaccine 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." As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the CDC, WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.