Full FDA approval could drive COVID-19 vaccinations, but experts advise against waiting

One-third of unvaccinated U.S. adults say they will only get in line for the COVID-19 jab once it's fully approved, but medical experts say it can also be risky to wait.

Moderna became the latest COVID-19 vaccine maker to apply for full approval by the Food and Drug Administration, announcing last week that it has started the process for approval in people ages 18 and up. That follows Pfizer's announcement in early May that it was seeking approval in those ages 16 and up.

About half the country so far has gotten at least one dose of the COVID-19 vaccine, which has been made available in the U.S. through an emergency use authorization due to the public emergency the pandemic poses. As vaccination rates decline, full FDA approval could give them a boost, as the distinction holds significance for a large chunk of people who remain unvaccinated. According to the Kaiser Family Foundation's latest vaccine monitor report, nearly a third -- 32% -- of unvaccinated adults are waiting for full FDA approval of a vaccine before getting it.

Dr. William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, said the large share of those waiting for approval came as a surprise.

"My sense is that it probably means more to the general public than it actually should," Moss told ABC News. "To think that that approval process is going to be the be-all and end-all is misguided to me."

Both authorization and approval are rigorous processes that look at the safety and efficacy of a vaccine, Moss said. A key difference between the two is that at least two months of follow-up data from phase 3 clinical trials are considered for authorization, versus at least six months for approval.

The FDA will take several months to review the full set of data before granting approval, which several experts told ABC News was very likely. For Moss, with nearly 300 million doses administered in the U.S., "there's nothing about that review process that's going to reveal anything we don't know."

"Yes, it's kind of a formal stamp of approval, but I don't think it really provides much more than what we already know," he said. "We have more data on vaccine safety than with any other vaccine, even before the review of the full approval."

Both Pfizer and Moderna have said their vaccines continued to offer strong protection at six months after a second dose, including against emerging variants, and reported no serious safety concerns. The Vaccine Adverse Event Reporting System also provides transparency and helped identify the very rare chance of blood clotting some were diagnosed with after getting the Johnson & Johnson vaccine.

Full approval would allow the vaccines to be used after the public health emergency is over in the U.S. It will also allow the companies to advertise their vaccines to people, which could help encourage vaccination, Dr. James McDeavitt, senior vice president and dean of clinical affairs at Baylor College of Medicine, told ABC News.

"I think there's a significant benefit if we start to have some privately produced, professionally produced advertisements that are gonna encourage people to get vaccinated," he said. "It could be a significant driver."

At the same time, McDeavitt would also encourage people not to wait for approval if they plan to get the vaccine.

"If you wait a month or two or three, you're exposing yourself to risk that is unnecessary and preventable," he said. "[The COVID-19 vaccine is] free, it's incredibly safe and it's readily available. In my personal opinion, it makes no sense to wait."

Dr. John Brownstein, an epidemiologist at Boston Children's Hospital and an ABC News contributor, said that if waiting for approval gets more people vaccinated, that's a positive, but he also said there are risks in waiting as COVID-19 transmission remains active.

"All signs point to the full approval," he said. "So that may factor into the decision, of expected approval versus the potential risk of being unvaccinated."

Beyond approval, paid time off was another sticking point for people who are not yet vaccinated. The Kaiser Family Foundation survey found that 21% of employed, unvaccinated adults would be more likely to get the vaccine if their employer gave them paid time off to get it and recover from side effects.

Additionally, between 10% and 15% of unvaccinated adults said they would be more likely to get the vaccine if there was a financial incentive, such as money or free tickets, the survey found.

Seven percent said they would get vaccinated "only if required." Full FDA approval could open the door to more companies and schools mandating it, further increasing vaccine uptake, Brownstein said.

"I think we will see an opening up of more vaccine mandates by employers or other institutions, even perhaps government institutions," Moss said. "I think they will feel more comfortable mandating that their employees get vaccinated, obviously with certain rules about exemptions, after a full approval."