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  • Millions of Americans are now eligible for a second booster, at least four months after their first one.
  • The FDA has authorized a second COVID-19 booster shot for people over age 50.
  • Some immunocompromised people will also be eligible for a second booster dose at least four months after their first booster.

This is a developing story. Check back for updates.

Today, the Food and Drug Administration on Tuesday authorized a second COVID-19 booster for people 50 years of age and older and for certain people who are immunocompromised.

This will help people at higher risk of severe COVID-19 to get extra protection as the coronavirus regains ground in many states due to the BA.2 Omicron sublineage.

The FDA’s decision clears the way for people age 50 and older to get a fourth dose of the Pfizer-BioNTech or Moderna vaccine at least four months after their previous booster.

Certain immunocompromised people will also be eligible for a second booster dose at least four months after their first booster. The Pfizer-BioNTech vaccine is available to those 12 years of age and older, and the Moderna vaccine to those 18 years of age and older.

People 12 years and older with moderately or severely weakened immune systems were previously eligible for a three-dose primary series followed by a single booster.

The FDA’s move will allow millions more Americans to get an extra dose. But two key questions remain: who should get a second booster and when?

The Centers for Disease Control and Prevention (CDC) will likely weigh in on these questions in the coming days.

A second booster is being made available only to these higher-risk groups because studies suggest that they may benefit the most from an additional dose.

“Current evidence suggests some waning of protection over time against serious outcomes from COVID-19 in older and immunocompromised individuals,” Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said Tuesday in a news release.

In addition, “based on an analysis of emerging data, a second booster dose of either the Pfizer-BioNTech or Moderna COVID-19 vaccine could help increase protection levels for these higher-risk individuals,” he said.

Although coronavirus cases in the United States have dropped drastically since the January peak of the Omicron surge, cases are rising again in 13 states and the District of Columbia.

This is being driven in part by the BA.2 Omicron sublineage, which has also caused a sharp jump in cases in many European countries.

BA.2 accounts for over half of sequenced cases in the United States, according to CDC estimates.

Although the FDA is moving forward with second booster doses for certain American, a single booster still offers protection against severe outcomes.

Recent CDC data shows that two mRNA vaccine doses and a booster provided over 90 percent protection against death or needing mechanical ventilation, even as vaccine efficacy against infection has waned over time.

In that study, the protection against severe outcomes was lowest among people with weakened immune systems. However, the vast majority of those hadn’t received a third dose, so they weren’t considered fully vaccinated.

“The data show that an initial booster dose is critical in helping to protect all adults from the potentially severe outcomes of COVID-19,” said Marks in the FDA release. “So, those who have not received their initial booster dose are strongly encouraged to do so.”

Data on the benefits of fourth doses is limited, with most benefits seen in higher-risk groups.

A recent large Israel study, not yet peer-reviewed, showed that a second booster reduced the risk of death by 78 percent among people age 60 and older compared to those with only one booster.

In addition, the FDA reported Tuesday that its review of data on 700,000 fourth doses given in Israel revealed no new safety concerns.

The Israeli study only followed people for 40 days after their second booster, so it’s not clear how long any benefits from this extra dose would last.

If protection against COVID-19 wans similar to what has occurred with two doses, it makes sense to get the second booster closer to the start of a surge.

Predicting when a surge will happen, though, is difficult. Even with the BA.2 Omicron sublineage, it’s not clear if it will cause a similar spike in cases in the United States as it has in Europe.

So deciding on a second booster comes down to weighing your personal risk and comfort level.

“I would recommend the 2nd booster if you are more than 4 to 6 months from your 3rd shot, you are age 50+, you tolerated the previous shots well, and you are concerned about the BA.2 wave where you live,” Dr. Eric Topol, director and founder of the Scripps Research Translational Institute, wrote in a post.

However, “it’s also fine to wait if there’s a low level of circulating virus where you live and work,” he said.

In addition, Topol said if you’ve had three doses and a breakthrough infection, you likely won’t need a second booster at this point because you have some “hybrid immunity,” which will provide added protection for some time.

But he also reiterated what the FDA’s Marks said.

“If you haven’t had your 1st booster, you’re long overdue to get it,” said Topol. “It was lifesaving vs. Delta for people age 50+, and vital for maintaining a high level of protection vs. severe disease from the Omicron family of variants.”