As we dive into summer, public health experts say a booster shot targeted at Covid's omicron variant can better protect Americans during a possible virus surge in the fall.

On Thursday, the U.S. Food and Drug Administration recommended that drugmakers like Pfizer and Moderna move ahead with developing omicron-specific booster shots for the coming fall. Both companies have already started designing boosters based on omicron's BA.1 and BA.2 subvariants — and the FDA encouraged them to forge ahead with new booster formulations targeting omicron's newer, more infectious BA.4 and BA.5 subvariants.

The FDA noted that these shots should be developed, tested and hopefully approved for use "starting in early to mid-fall 2022." That timing could be important: In May, the Biden administration warned of a Covid surge this fall and winter that could result in 100 million new infections and a wave of deaths.

In other words, the odds are high that you'll need to get a new Covid shot this coming fall. Here's what experts say you should know, from vaccine effectiveness to what the latest timelines realistically look like.

Will these boosters protect you against the new omicron subvariants?

So far, it's unclear — but clinical data from Pfizer and Moderna on the boosters they've already made for BA.1 and BA.2 is promising.

The data suggests that those shots provide noticeably stronger immunity against their targeted subvariants than the primary vaccines most Americans have already received. As with all vaccines, the goal isn't necessarily to completely stamp out transmission — no vaccine is 100% effective at preventing illness — but updated boosters could further bolster your protection against hospitalization or death.

The shots didn't achieve quite the same results against BA.4 and BA.5, but still generally performed well. The FDA's hope is that updated boosters will more effectively combat those newer subvariants by the fall., and the Biden administration already has an agreement with Pfizer to purchase 105 million doses of whichever booster formulation ultimately gets approved, the U.S. Department of Health and Human Services announced on Wednesday.

Of course, new variants or subvariants could emerge between now and the fall, potentially sending drugmakers back to square one. But having vaccines that already target a specific Covid strain is still a good first step, because updating them for new strains is easier than creating them in the first place.

"[It] places us in a relatively good position," Dr. Ali Khan, an epidemiologist and dean of the College of Public Health at the University of Nebraska Medical Center, tells CNBC Make It.

Who will be eligible for the new vaccines?

Crucially, the FDA's announcement on Thursday noted that the omicron-specific vaccines will likely serve only as booster shots, meaning the country's current slate of approved vaccines will probably remain for primary vaccination series.

That means you'll only be eligible to get an omicron-specific booster if you're already up-to-date on your vaccinations. Manufacturers may also need time to develop enough boosters for all age groups, which could mean vaccinating the population in tiers, Khan says.

"If there's sufficient vaccine available, then that may not be necessary," he adds. "It's really hard to predict, because this all comes down to manufacturing schedules at this point."

Khan says the Centers for Disease Control and Prevention faces similar issues each year when developing new influenza vaccines: It must decide months in advance what the new flu vaccine is going to look like, so enough doses can get manufactured to meet demand by the fall.

"The decisions around flu are made just before spring, whereas now we're way into the summer to make this decision about vaccinating in the fall for Covid," says Khan.

Is this the start of annual vaccination against Covid?

The short answer: Probably yes, according to Dr. Michael Merson, a professor of global health at Duke University.

Once omicron-specific vaccines are approved for general use, it'll be much easier for vaccine-makers to create new versions of their booster shots each year for the latest circulating Covid strains. And while protection against infection typically wanes four months after receiving a booster shot, according to the CDC's data, vaccinated individuals have strong protection from hospitalization and death for much longer.

"We've seen from the trials so far that, with omicron, we do get longer protection against serious illness, hospitalization and death — which, of course, is the most important endpoint," Merson says. "If our goal is that, primarily, which I think it should be, then a yearly vaccine would seem adequate."

If the aim is to prevent infection and mild illness, then vaccinating every few months would be the solution, but Merson doesn't "believe that is a realistic goal" at this point.

Historically, experts have pointed to the fall as a target range because Covid has long been expected to fall into a seasonal pattern, getting worse in colder months and better in warmer months. Merson notes that this hasn't exactly happened yet — but fall remains a target deadline, largely because it's the soonest anyone should realistically expect the drug-making and approval processes to safely take.

Until the FDA decides on the vaccine's composition and reviews clinical data from multiple companies, the new vaccines will not be manufactured in large quantities, he adds. 

"They think there could be a vaccine by October. Now, that's not ideal. Ideally, you'd like to have it a little sooner maybe," says Merson. "But at least it's early enough for the winter season."

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