Full FDA approval of Pfizer’s Covid-19 vaccine had only a modest impact on uptake. Here’s what mattered more

By Elizabeth Cohen, CNN Senior Medical Correspondent

Despite hopes that full approval of Pfizer’s Covid-19 vaccine would convince large numbers of vaccine-hesitant Americans to roll up their sleeves, a federal government analysis provided to CNN suggests approval was not a silver bullet.

After the US Food and Drug Administration granted full approval to Pfizer’s shot in August, Pfizer vaccination rates did increase, but the uptick was modest and relatively short-lived.

“There weren’t suddenly lines around the block,” said Becca Siegel, senior adviser to the US Department of Health and Human Services’ public education campaign.

The data backs up what a recent poll found: While full approval might matter to some unvaccinated Americans, it’s likely not going to be the sole reason unvaccinated Americans will roll up their sleeves.

“For truly undecided people, this is a complex decision. It’s not one thing,” Siegel said.

According to the poll, another factor is more persuasive than full approval: Fear — fear of dying of Covid-19 or of missing out on activities such as travel, concerts or sporting events that require vaccination.

This leaves federal officials in the middle of a long, slow slog to get unvaccinated Americans to finally get vaccinated and help put an end to the pandemic. Currently, 75.8% of eligible Americans have received at least one dose of a Covid-19 vaccine, according to the US Centers for Disease Control and Prevention — a number that has inched upward only very slowly in recent months.

Summer polls offered high hopes

On August 23, the day the FDA issued full approval to Pfizer/BioNTech’s Covid-19 vaccine, President Joe Biden pleaded with unvaccinated Americans.

“If you are one of the millions of Americans who said they will not get the shot until it has full and final approval of the FDA, it has now happened. The moment you’ve been waiting for is here. It’s time for you to go get your vaccination, and get it today — today,” Biden said.

Biden had good reason for optimism.

According to a poll conducted in June by the Kaiser Family Foundation, about half of people who were taking a “wait and see” approach to vaccination said they would be more likely to get vaccinated if the FDA fully approved one of the Covid-19 vaccines.

“Many unvaccinated people worry that the vaccines are experimental and fears about the safety of the vaccine are a major reason some groups are hesitant to vaccinated,” Drew Altman, Kaiser’s president and CEO, wrote in August. “Lack of FDA approval has allowed the idea that the vaccines are unsafe or ineffective to fester.”

A modest, short-term increase after full approval

It turned out the FDA’s full approval did help to change some minds, but the effect was not dramatic.

From August 23 to September 3, the seven-day average of the administration of Pfizer doses increased by 16%, from 575,000 per day to 668,000 per day, according to the HHS analysis. In comparison, uptake for Moderna’s vaccine, which has emergency use authorization but not full approval, increased by 5% during that time.

Of course, an increase in vaccination rates can be due to many factors. But the increase in Pfizer’s vaccine following approval is especially notable because in the weeks prior to full approval, Moderna was seeing larger increases than Pfizer, according to an analysis done for CNN by the Computational Epidemiology Lab at Boston Children’s Hospital, which powers the Vaccines.gov website.

After September 4, the seven-day averages for both vaccines started to decline.

Running ‘the last mile’

A September poll might help explain why full licensure didn’t have more of an effect.

A Kaiser Family Foundation poll conducted last month showed that FDA approval played a relatively minor role in vaccine decision making.

In that survey, only 15% of recently vaccinated people said full approval of Pfizer’s vaccine was a major reason they got the shot, and only 2% said it was the main reason.

The Kaiser poll found that other factors were more likely to be a major reason for getting vaccinated: the increase in cases due to the Delta variant; concern about hospitals filling up with Covid-19 patients; knowing someone who became seriously ill or died from Covid-19; wanting to participate in certain activities, such as travel; being required to get a vaccine by an employer; and social pressure from family and friends.

Siegel, the HHS analytics and public opinion expert, said she thinks full approval could still play a role long-term — in combination with other factors — in convincing people to get a shot.

“We won’t see the impact of approval on day one, hour one, but could see it over a long period of time,” she said.

About 1 in 4 eligible Americans has not gotten even one shot of a Covid-19 vaccine, and Siegel noted there’s no simple way to convince them.

“This is a slow, steady march,” she added. “It’s not getting easier, and it won’t get easier.”

The fact that nothing so far — not full approval, not overflowing hospitals, not 700,000 dead Americans — has convinced tens of millions of Americans to get vaccinated is reason enough for mandates, some experts say.

“I think we’ve come to recognize that mandates are what we’ve come to in order to really generate increases in vaccination,” said John Brownstein, director of the Computational Epidemiology Lab at Boston Children’s Hospital and a professor at Harvard Medical School. “Mandates are super important to cover the last mile for those who are on the fence.”

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CNN’s Deidre McPhillips and Virginia Langmaid contributed to this report.