Federal health officials expressed optimism on Tuesday that the nation was better prepared to weather a surge of Covid-19 infections this winter compared with a year earlier, and they renewed their pleas for Americans to get an updated booster shot ahead of the holidays.
While the trajectory of the virus remains uncertain, Dr. Anthony S. Fauci, President Biden’s chief medical adviser, said the administration was hopeful that the combination of infections and vaccinations had created “enough community protection that we’re not going to see a repeat of what we saw last year at this time” when a brand-new variant, Omicron, emerged seemingly out of the blue.
As families gather for Thanksgiving, officials have been watching a new subvariant of Omicron, XBB, with some trepidation. That subvariant, which drove a wave of infections in Singapore and India, appears much better able to evade the antibodies that are created by prior infection or vaccination. Antibody protection, which forms the body’s first line of defense against the virus, “is diminished multifold with XBB,” Dr. Fauci said at a White House briefing.
But he said officials were encouraged by data showing that the surge of infections from XBB in countries like Singapore was not matched by a commensurate rise in hospitalizations. Experts have long said that other parts of the immune system can kick in to ward off severe disease if the virus dodges the antibodies.
Federal officials emphasized the importance of booster shots in helping to fortify the country against a potential uptick in cases, but Americans have so far been slow to embrace the new shots. Nearly three months after the administration rolled out the updated doses, only about 35 million people have received one of the new shots from Pfizer-BioNTech or Moderna.
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The administration bought roughly five times as many doses. Health providers say many Americans are simply weary of repeated vaccinations three years into the pandemic.
As officials urged Americans to protect themselves with the vaccine, the Centers for Disease Control and Prevention delivered what officials cast as encouraging news about the effectiveness of the updated shots. A major new study, the agency said, shows that the updated coronavirus boosters bolstered protection against symptomatic disease among adults by 28 to 56 percent.
The results were better among those who had their last dose of the original vaccine at least eight months earlier. “Is this a home run? No, but it’s a good base hit,” said Dr. Peter Marks, the top vaccine regulator at the Food and Drug Administration, who pushed for development of the new shots.
The study looked at 360,000 adults who reported Covid-19 symptoms between mid-September and mid-November. Its significance is limited by the fact that the Omicron subvariant that accounted for the largest number of cases during that period, BA.5, has receded and now accounts for only a quarter of cases. Still, it is the first published real-life study of the effectiveness of the vaccine, the C.D.C. said.
Another study released by the C.D.C. underscored the effectiveness of Paxlovid, an antiviral medication recommended for adults with mild to moderate symptoms of Covid-19 who have a higher risk of severe illness.
Adults diagnosed with Covid who were prescribed Paxlovid had a 51 percent lower hospitalization rate within 30 days of their diagnosis than those who were not prescribed the medication, the study found. For a five-month period ending in August, researchers compared nearly 200,000 adults who received Paxlovid within five days of their diagnosis with more than 500,000 people who did not receive it. Many had been previously infected with the coronavirus or had been vaccinated.
The study found that only 28 percent of eligible adults were prescribed Paxlovid. The researchers said the medication should be offered to everyone eligible, especially older adults and people with multiple underlying health conditions.
Zolan Kanno-Youngs contributed reporting.