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Illustration: Annelise Capossela/Axios

As the Delta variant continues to drive a fourth wave of the coronavirus pandemic in the U.S., Biden officials see a booster shot among at least some vaccinated Americans as increasingly likely.

Why it matters: Another round of shots — beginning as early as late fall — could not only boost the level of protection against the virus among the vaccinated, but also help curb its spread throughout the population.

Between the lines: The amount of neutralizing antibodies a person has following their first two doses of Pfizer and Moderna's coronavirus vaccines appears to drop over time, which is a very normal thing to happen with vaccines.

  • The outstanding scientific question has been what that means for the person's overall protection against the virus, especially because neutralizing antibodies aren't the body's only form of immunity.
  • Some Biden officials are increasingly convinced that high levels of neutralizing antibodies correlate with a higher degree of protection against illness. They worry that means that as more time passes, vaccinated people may be increasingly vulnerable to mild, moderate or even severe disease, a Biden official told Axios.

The New York Times first reported on Friday that Biden administration health officials increasingly think that vulnerable populations will need booster shots.

  • This growing consensus is "tied in part to research suggesting that the Pfizer vaccine is less effective against the coronavirus after about six months," per the NYT.
  • Vaccine manufacturers have been warning for months that some Americans could require booster shots as soon as September.

The big picture: There's currently no data suggesting that people who have received a shot — even those who were among the first to get vaccinated — are at risk of becoming severely sick if they get a breakthrough infection.

  • That doesn't mean they never will be. And recent data suggest that protection against asymptomatic or mildly symptomatic disease does decrease over time.
  • Although vaccine efficacy against severe disease seems to be holding steady among the three vaccines authorized for use in the U.S., some officials worry that may not continue to be true, the Biden official said, adding that boosters could begin as early as late fall.

Officials also believe that a booster shot may reduce the chances that a vaccinated person can transmit the virus, which would help reduce its overall prevalence in the U.S. — particularly if the Delta variant causes cases to rise as much as it's predicted to.

What we're watching: The Biden administration has purchased enough doses of vaccine to ensure that the U.S. will have enough for anyone who wants a booster to receive one.

  • The rest of the world, however, is likely to question why Americans should receive a third shot while billions of people around the globe wait for their first.

Go deeper

Sep 25, 2021 - Health

America has fallen behind on vaccinations

Data: Our World in Data; Chart: Will Chase/Axios

The U.S. has fallen from the top of the world's list of most-vaccinated countries, largely due to the substantial percentage of Americans who don't want the vaccine.

What we're watching: Vaccine mandates are becoming much more common in the U.S., and children under 12 will likely become eligible for vaccines within the next few months — both of which should help boost the vaccination rate here.

Sep 25, 2021 - Health

More virus, more risk, more social distancing

Expand chart
Data: Axios/Ipsos poll; Chart: Will Chase/Axios

When the Delta variant caused coronavirus infections to spike over the summer, Americans began thinking of COVID as a larger risk and resumed social distancing.

Why it matters: Life won't look normal until there's much less virus around — even if the majority of the population is vaccinated — as millions of people will voluntarily try to avoid it.

Go deeper: America's mismatched COVID fears

Sep 25, 2021 - Health

Long COVID: A disabling disease

Illustration: Annelise Capossela/Axios

Millions of Americans are still suffering from a wide spectrum of symptoms long after they've recovered from their original coronavirus infections, and it's very unclear what the disease's trajectory is — or even how many people are affected.

What we're watching: We still don't have a good grasp on how susceptible vaccinated people are to long COVID. If the condition remains a threat even for the vaccinated, that could shape the risks people are willing to take in the future.