The Food and Drug Administration on Monday gave Pfizer-BioNTech’s coronavirus vaccine full approval for people aged 16 and over, making it the first to go beyond emergency status in the United States.

The decision will trigger a cascade of vaccine requests from hospitals, colleges, corporations, and other organizations. Secretary of Defense Lloyd J. Austin III will send vaccination guidelines to the country’s 1.4 million active military personnel, the Pentagon said on Monday.

United Airlines recently announced that its employees must provide proof of vaccination within five weeks of regulatory approval.

Oregon has introduced a similar requirement for all government employees, as have a variety of universities in the states of Louisiana through Minnesota.

Approval comes as the nation’s fight against the pandemic has re-intensified, with the highly contagious Delta variant dramatically slowing the country’s progress in the first half of the year. The Biden administration hopes the development will motivate at least some of the roughly 85 million unvaccinated Americans eligible for syringes.

President Biden plans to commemorate this in a speech urging vaccination, which is scheduled for 1:30 p.m. Eastern time on Monday afternoon. “If you haven’t been vaccinated, now is the time,” the president said on Twitter.

“While millions of people have safely received Covid-19 vaccines, we recognize that FDA approval of a vaccine may now create additional confidence for some to get vaccinated,” said Dr. Janet Woodcock, acting FDA commissioner, in a statement. “Today’s milestone brings us one step closer to changing the course of this pandemic in the US”

Pfizer said it provided the FDA with data from 44,000 participants in clinical trials in the United States, the European Union, Turkey, South Africa and South America. The company said the data showed the vaccine 91 percent prevented infection – a slight decrease from the 95 percent effectiveness rate the data showed when the FDA decided to approve the emergency vaccine in December. Pfizer said the decrease reflects the fact that researchers had more time to capture infected individuals.

A recent survey by the Kaiser Family Foundation, which tracked public attitudes during the pandemic, found that three in ten unvaccinated people said they were more likely to be vaccinated with a fully approved vaccination.

But pollsters and other experts warned that the percentage could be exaggerated. “I think that’s a tiny number of people in real life,” said Alison Buttenheim, an associate professor of nursing at the University of Pennsylvania and an expert on vaccination hesitation.

More important, says Dr. Buttenheim, is the effect of requirements. “Mandates make things easier for people,” she said.

Government action gives doctors more leeway to prescribe patients a third shot of the Pfizer vaccine, but federal officials strongly advised people not to seek additional vaccinations until regulators decide they are safe and effective. Pending regulatory approval, the federal government plans to offer booster syringes for adults next month.

The vaccine continues to be approved for emergency use in children ages 12-15 as Pfizer collects the data necessary for full approval. A decision on whether to approve the vaccine for children under the age of 12 could be at least several months away, and Dr. Woodcock said no child this age should get a Covid-19 vaccine due to a lack of safety data from regulators.

To date, more than 92 million Americans – 54 percent of those fully vaccinated – have received Pfizer vaccinations. Most of the others got the vaccine from Moderna.

Dr. Peter Marks, the FDA’s lead vaccine regulator, said the approval of Pfizer vaccine followed a rigorous review of hundreds of thousands of pages of data and included inspections of the factories where the vaccine is made. “The public and the medical community can rest assured that while we were swiftly approved this vaccine, it met our existing high standards for vaccines in the United States,” he said.

He said federal health officials would continue to monitor the safety of the vaccine and that the FDA would require Pfizer to assess the risks of myocarditis, an inflammation of the heart muscle, and pericarditis, an inflammation of the membrane surrounding the heart, including long-term results for the recipients. The FDA added warnings to the Pfizer-BioNTech and Moderna vaccines in June indicating a possible increased risk for these conditions after the second dose.

Although Pfizer can now market the drug under the Comiraty name, the company said only the federal government will be distributing doses in the United States.

Understand US vaccination and mask requirements

    • Vaccination rules. On August 23, the Food and Drug Administration fully approved Pfizer-BioNTech’s coronavirus vaccine for people aged 16 and over, paving the way for increased mandates in both the public and private sectors. Private companies are increasingly demanding vaccines for employees. Such mandates are legally permissible and have been confirmed in legal challenges.
    • Mask rules. The Centers for Disease Control and Prevention in July recommended that all Americans, regardless of vaccination status, wear masks in public places indoors in areas with outbreaks, reversing the guidelines offered in May. See where the CDC guidelines would apply and where states have implemented their own mask guidelines. The battle over masks is controversial in some states, with some local leaders defying state bans.
    • College and Universities. More than 400 colleges and universities require a vaccination against Covid-19. Almost all of them are in states that voted for President Biden.
    • schools. Both California and New York City have introduced vaccination mandates for educational staff. A survey published in August found that many American parents of school-age children are opposed to mandatory vaccines for students but are more likely to support masking requirements for students, teachers and staff who are not vaccinated.
    • Hospitals and medical centers. Many hospitals and large health systems require their employees to have a Covid-19 vaccine, due to increasing case numbers due to the Delta variant and persistently low vaccination rates in their communities, even within their workforce.
    • New York City. Proof of vaccination is required by workers and customers for indoor dining, gyms, performances, and other indoor situations, though enforcement doesn’t begin until September 13. Teachers and other educational workers in the city’s vast school system are required to have at least one vaccine dose by September 27, with no weekly testing option. City hospital staff must also be vaccinated or have weekly tests. Similar rules apply to employees in New York State.
    • At the federal level. The Pentagon announced that it would make coronavirus vaccinations compulsory for the country’s 1.3 million active soldiers “by mid-September at the latest. President Biden announced that all civil federal employees would need to be vaccinated against the coronavirus or undergo regular tests, social distancing, mask requirements and travel restrictions.

Health experts and state officials welcomed the development. With the delta variant driving up case numbers across the country, “full approval could not come at a more important time,” said Dr. Richard Besser, President of the Robert Wood Johnson Foundation and former acting director of the Centers for Disease Control and Prevention. He urged schools and businesses to require a vaccination before people can gather indoors.

Less than two months after the spread of the virus appeared to be contained, the US is now recording an average of around 150,000 new cases per day and more than 90,000 hospitalized Covid-19 patients. An average of around 1,000 per day die from Covid-19 – a toll that federal health experts recently dismissed as highly unlikely before the delta variant fully caught on. Many children under the age of 12 also become infected.

Vaccination rates have also risen in the past few weeks, in part because of the greater fear of the virus. Vendors were delivering approximately 837,000 shots a day, a significant increase from earlier this summer.

Some experts estimated that full consent could only convince five percent of the unvaccinated to get injected. Even if that is the case, “that is still a huge part of the people,” Dr. Thomas Dobbs, the Chief Health Officer of Mississippi, a state particularly hard hit by the Delta variant. He said the approval will help “get rid of this false claim that the vaccines are an ‘experimental’ thing”.

Dr. Marks, the vaccines agency, cited a number of other myths about the vaccines as a major stumbling block in fighting the pandemic, including false claims that the vaccinations cause infertility, promote Covid disease rather than prevent it, or have resulted in thousands of deaths. “Let me be clear. These claims are just not true,” he said.

The FDA is in the middle of a decision marathon related to coronavirus vaccines. The next important question emerging for regulators is whether or not to approve booster injections. The Biden government said last week it plans to offer third vaccinations starting September 20, for adults who received the Pfizer and Moderna vaccines eight months after their second injection. Third vaccinations are already approved for some people with immunodeficiency, but the risk-benefit ratio is different for the general population.

Federal health officials said that both Pfizer-BioNTech and Moderna’s vaccines, which are based on similar technology, lose effectiveness over time. That trend is converging with the advent of the particularly dangerous Delta variant, making those who completed their vaccinations earlier in the year increasingly more susceptible to infection.

Some health experts have challenged the decision to recommend booster vaccinations as premature, as the data showed the vaccines withstand serious illness and hospitalization, including the Delta variant. Boosters would only be justified if the vaccines didn’t prevent hospital stays with Covid-19, some of these experts said.

Regulators are still examining Moderna’s application for full approval of its vaccine. This decision can take several weeks. Johnson & Johnson is expected to file for full approval shortly.

Helene Cooper contributed to the reporting.