Only a Small Percentage of Americans Can Get Boosters Now. Here's Why — and What It Means for You

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After weeks of regulatory drama, booster shots are finally almost here.

On Friday, Centers for Disease Control and Prevention director Dr. Rochelle Walensky approved boosters of Pfizer's Covid vaccine for a selection of vulnerable Americans, ending a lengthy back-and-forth debate between advisory panels at the Food and Drug Administration and the CDC.

Americans 65 and older, long-term nursing home residents and adults aged 50-64 years with medical conditions like diabetes or cancer will now become booster-eligible six months after their second Pfizer dose. Any Pfizer recipient aged 18-64 with a high risk of severe illness or Covid exposure in the workplace may also choose to get a booster six months after their second dose, based on their own individual risk and benefit.

On Wednesday, the FDA authorized third-dose boosters of Pfizer's Covid vaccine for the same groups.

If you fall into one of those categories and got your second dose in March or earlier, you can get a booster shot immediately. During a White House address Friday, President Joe Biden said pharmacies, doctors and health centers across the country are already prepared for a national booster rollout.

The authorization only affects people who have already received two shots of Pfizer's vaccine. Moderna and Johnson & Johnson haven't submitted booster applications to the FDA yet, but Walensky said that the CDC "will address, with the same sense of urgency, recommendations for the Moderna and J&J vaccines as soon as those data are available," in a statement Friday.

The decision shuts the door on many younger Americans getting a third-dose booster shot, at least for now. The 65-and-older group makes up around 17% of the U.S. population. According to the CDC, the immunocompromised group is only roughly 3%.

The agency's recommendation could broaden in the future: With this approval, the FDA signaled that older people and those with underlying conditions simply need greater protection right now.

Experts say that's unsurprising. Somewhat more unexpected, though, is the other rationale given by an FDA advisory panel last Friday: the potential for a side effect in young adults called myocarditis, or inflammation and weakening of the heart.

Developing myocarditis after getting the mRNA Covid vaccines is rare, according to CDC data released on Sept. 3. And Dr. Eric Stecker, chair of the American College of Cardiology Science and Quality Council, says cases associated with Covid vaccines tend to be mild, and resolve on their own without treatment in a matter of days.

The condition tends to be more prevalent in young people, specifically men under 30. And according to the FDA panel, the odds of heart inflammation could grow with a third dose of a Covid mRNA vaccine.

Why the concern over boosters has 'been blown a bit out of proportion'

But for other experts, the jury is still out — and other countries are already forging ahead.

In Israel, for example, anyone as young as 12 can get a booster shot. Since the boosters became available for all ages in late August, there was only one case of myocarditis reported out of the 2.8 million people who've received three doses, according to data from Israeli researchers also released on Sept. 17.   

Until there's data from ongoing clinical trials in the U.S. looking specifically at the effect of booster doses, "we don't know if the myocarditis issue would be more serious or not after a third dose versus after a second," Stecker says.

It might seem dramatic that the FDA rejected boosters for most adults over something so rare and conceivably mild.

"It's been blown a bit out of proportion," Gigi Gronvall, an immunologist at the Center for Health Security at the Johns Hopkins Bloomberg School of Public Health, tells CNBC Make It. Covid infections cause heart inflammation at much higher rates than the Covid vaccines do, she says.

The FDA is responsible for paying extremely close attention to vaccine side effects, Stecker says, noting that the agency's principal role is to determine whether the need for booster doses in young people outweighs the potential risks.

"I would hope that people would interpret the fact that there's all this press and attention around a very mild and very rare side effect of vaccines, illustrates that that policymakers and scientists are taking this issue very seriously, are being very transparent about it," Stecker says.

Experts aren't entirely sure why myocarditis pops up after Covid vaccination, or why it's more prevalent in young men. Stecker says it could be that young people's immune systems are more robust that older people's, meaning they have stronger reactions to the vaccines — a double-edged sword, since stronger reactions also tend to result in better anti-virus protection.

"There's no question that the benefits of avoiding those deaths, ICU admissions and hospitalizations definitely outweigh the risks of these, basically, 40 to 50 cases of mild myocarditis," he says.

What this means for potential booster shots down the road

You might be wondering what all of this means for you when it's time to get your booster shot.

If you're under 65 with no underlying conditions, and you don't work somewhere that regularly exposes you to Covid, you'll probably need to wait a while. That group may only get approved if vaccine protection eventually wanes to a severe degree — so much that the vaccines no longer reduce severe disease and prevent hospitalization and death.

"My bottom line is that the general population will not need boosters," says Dr. William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health. "But that's with the understanding that our goal with vaccination is to reduce severe disease to prevent hospitalization and death."

Boosters could also get approved for most Americans if a new vaccine-evading variant emerges. Currently, two doses of an mRNA Covid vaccine work well at preventing severe illness, hospitalization and death, even against variants like delta.

People who got the one-shot Johnson & Johnson vaccine could become booster-eligible sooner, though a public timeline doesn't exist yet. On Tuesday, J&J released new data showing that its booster shot is 94% effective when administered two months after a first dose. Other studies are currently examining the effect of mixing and matching mRNA vaccines with J&J's one-shot.

Jumping the line to get a booster before you're eligible is ethically questionable at best, and raises serious public health concerns nationwide.

Doing so makes it harder for the CDC to accurately track how many people are vaccinated, and distracts from the country's primary objective of getting unvaccinated people vaccinated, Moss says.

Update: This story has been updated with the CDC's approval of booster shots and President Biden's announcement of a national rollout.

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