Collins said that breakthrough infections are "relatively uncommon," but Israeli researchers found higher rates of infection among those who received their second dose of vaccines in mid-January than those who completed their shots in February or March. This shows that vaccine-induced immunity wanes over time.
An Israeli report published on October 27 said that the association between the rate of confirmed infections and the period of vaccination provides a measure of waning immunity. "Without waning of immunity, one would expect to see no differences in infection rates among persons vaccinated at different times," the report added.
Meanwhile, Pfizer asked federal regulators to authorize its coronavirus booster shots for individuals 18 years old and older, a move that would make every adult in the U.S. eligible for the extra injection.
The Food and Drug Administration (FDA) is expected to grant the requests before Thanksgiving and well ahead of holiday travels and gatherings. The prospect of 181 million fully vaccinated adults having access to extra shots is a turnaround from a couple of months ago when an expert advisory committee to the FDA overwhelmingly recommended against boosters.
President Joe Biden initially wanted Americans to start getting their boosters in late September. However, it was delayed as regulators insisted they needed more time to review the safety and efficacy data of the shots. Other global public health experts also said it would be better to focus on getting the initial shots to poorer countries with low vaccination rates than to distribute extra shots in the U.S. too soon.
Currently, only individuals aged 65 years or older and adults who are at special risk due to medical conditions can get booster shots if they initially got Pfizer or Moderna vaccines. The FDA also authorized boosters for all Johnson & Johnson recipients because the vaccine offers less protection.
There had been nearly 25 million Americans who have gotten boosters so far, including those with immune deficiencies who became eligible in August. This sums up to around 14 percent of those who have been fully vaccinated. The number could rise sharply over time if all other adults become eligible for the Pfizer booster.
Immunity against milder infections appears to wane months after the initial vaccination. In the U.S., experts have been divided over whether or not booster shots are necessary for the population.
Some say that the vaccines continue to offer robust protection against severe diseases and hospitalization for healthy, younger individuals. However, there are also some who say that vaccinating around 60 million Americans older than 11 who haven't received their first doses yet should remain the highest priority. (Related: Scientists question the need for COVID-19 booster shots.)
Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky said: "We will not boost our way out of this pandemic."
But actions speak louder than words. Walensky actually overruled the advice of her own expert panel to make more people eligible for the booster.
Exactly who should get a booster was a contentious decision as CDC advisers spent two days poring over the evidence. Walensky endorsed most of their choices, including people 65 and older, nursing home residents and those ages 50 to 64 who have chronic health problems like diabetes. Those 18 and older with health problems can decide for themselves if they want a booster.
However, the CDC director overruled her advisers' objections and decided that an additional broad swath of the population also qualifies people at increased risk of infection because of their jobs or living conditions, including health care workers, teachers and people in jails or homeless shelters.
"This was scientific close call. In that situation, it was my call to make," Walensky said.
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