Omicron subvariant BA.5 now makes up the majority of COVID-19 cases in the US and has led to a summer wave of people getting infected for the first, second or third time. To best isolate the mutating virus, the US Food and Drug Administration in June made a recommendation that vaccine manufacturers should make a booster dose (a "bivalent" COVID-19 vaccine) that targets the BA.4 and BA.5 subvariants, as well as the older version of the virus.

Pfizer and BioNTech on Monday announced that they've asked the FDA to authorize its omicron-specific booster for people 12 years and older. Pending authorization, Pfizer's vaccine could be available this fall, possibly as early as September. But Pfizer's booster, which targets BA.5 in addition to an older strain of COVID-19, isn't the only vaccine in the running: Moderna's booster which targets the BA.1 version of omicron was approved in the UK last week. It isn't specific to BA.4/BA.5, however.

The pressure on the timeline to come up with a new vaccine comes partly from talk about expanding the eligibility of who can get a second booster of the currently available vaccines. (Only adults 50 and older and younger immunocompromised people are eligible for a second booster.) It also comes as Novavax, the newest COVID-19 vaccine to make the US market, won a recommendation from the CDC and FDA that allows it to be given to kids and teens as young as 12 as a primary series. (Novavax targets the older COVID-19 strains and isn't available as a booster yet for people who've been vaccinated.)  

The US Department of Health and Human Services on July 29 announced that it had ordered 66 million doses of Moderna's bivalent booster candidate, purchased with reallocated money meant for other COVID-19 resources as health officials have failed to secure more funding from Congress. 

While the US has also secured a previous order of 105 million doses of Pfizer, that isn't enough for all people in the US, the HHS said in the press release. Agreements with both vaccine companies would open up millions more doses, but this "can only be exercised" with more funding from Congress. 

Here's what we know about the fall COVID-19 vaccine strategy.

What are the BA.4 and BA.5 subvariants? 

Both BA.4 and BA.5 are considered part of the "original" omicron variant (BA.1) family. They're newer versions of the virus that causes COVID-19. BA.5 quickly overtook the conversation because of its extreme contagiousness, and it's now the dominant variant in the US. In a late June post, Dr. Eric Topol, professor of molecular medicine, called BA.5 "the worst version of the virus that we've seen."

While we're still living out the true effects of a BA.5 summer surge in the US, the new subvariant is thought to whittle away much of the infection protection people got from prior sickness, even with other omicron variants. 

Omicron caused such a huge number of cases last winter because it was the most contagious variant to date, evading some infection protection from prior illness and effectiveness of the vaccines. The fact that newer versions of omicron are proving to be even more contagious isn't a big surprise, as this is the path COVID-19 has taken over the last two and half years.

Read more about everything we know about BA.5. 

What is the FDA asking for? 

Specifically, the FDA is asking for a bivalent (two-component) vaccine booster, which will include the BA.4/BA.5 spike protein in addition to an older strain. The FDA doesn't make vaccines, so the agency will authorize individual vaccine types as companies create and test them, as it did for the original COVID-19 vaccines and booster doses. 

The vaccines currently authorized or approved only use older or "ancestral" strains of the virus. These vaccines still provide good protection against severe disease and death, but the effectiveness against infection is becoming more limited as the virus keeps mutating. 

Who will get a new vaccine and when can they get it?

Health officials now have their eyes on a September start date, moving the date up slightly from early October, White House COVID-19 Response Team Coordinator Dr. Ashish Jha said in a briefing in July.

But there isn't an authorized booster yet, so an exact timeline isn't available right now. Whenever the modified vaccine (or vaccines) are authorized and recommended, we may expect people who are more at risk for severe disease (including older adults and people with some health conditions, for example) to become eligible first, similar to the original COVID-19 vaccine campaign. 

However, if there's enough supply of new vaccines, NBC reports, health officials could make large swaths of people eligible for a new booster at once. Everyone age 12 and up, for example, or all adults 18 and older.  

But like the authorization timeline, the eligibility criteria isn't available yet. It's also possible that eligibility could be complicated by the fact that the HHS said it hasn't yet secured enough doses for all Americans because it needs more funding from Congress. The agency says it'll have 171 million new vaccine booster doses available this fall. There are about 199 million adults age 18 and older who are fully vaccinated in the US, according to the CDC. This means that if every fully vaccinated adult also decides to get a new booster when they become eligible, there won't be enough vaccine for 28 million adults without more doses purchased. 

What are the vaccine companies doing? Which company will make the new vaccine?

Moderna and Pfizer are both working on boosters that target the omicron variant, and the US government has agreements with those companies so doses from both will be available this fall, pending regulatory approval. Moderna's bivalent booster has already been approved in the UK. Pfizer and BioNTech have asked the FDA to authorize a booster that targets BA.5. 

Novavax, which just received the CDC's recommendation for its primary two-dose vaccine, also said it's speeding up work on a formula specifically targeting the new versions of omicron. But the US hasn't yet announced any plan to purchase or secure doses of Novavax, so it's likely Moderna or Pfizer (or both) will be the available vaccine, at least initially.

Johnson & Johnson, while still available in the US, has been recommended only for people who can't take, or don't want to take, another COVID-19 vaccine over risk of a very rare but dangerous side effect. J&J didn't respond to an earlier request for comment on the company's plans for the fall in the US.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.