As the highly contagious Delta variant spreads through the U.S., Covid-19 vaccination rates have picked up, particularly in states hit hard by recent surges. But just 51.5% of the total population and 60.3% of those 12 years and older are fully vaccinated, as mutations lead to more infectious versions of the coronavirus, and the number of daily shots in arms remains below spring highs. The U.S. Food and Drug Administration’s move to give the Pfizer -BioNTech vaccine full approval could boost those numbers.

The Pfizer vaccine was first cleared by regulators in December on an emergency-use basis for people 16 years and older, and in May it was authorized for children as young as 12. On Monday, it became the first Covid-19 vaccine to gain full FDA approval for those 16 years and older.

In June, before the Pfizer announcement, a third of unvaccinated adults said they would be more likely to get the shot if one of the vaccines had full approval from the FDA, according to a Kaiser Family Foundation survey of 1,888 adults, including 572 who hadn’t been vaccinated. The finding may be more of a proxy for general safety concerns, the foundation said.

News of variants such as Delta spreading in the U.S. has made about one in five unvaccinated adults more likely to get vaccinated, according to a July Kaiser survey. But in the three months leading up to the Pfizer announcement, the survey showed relatively little change in people’s vaccination plans, with 14% of U.S. adults planning to definitely not get a vaccine and about one in 10 planning to “wait and see” how the vaccine works for other people before getting vaccinated.

Vaccination requirements have been accelerating despite some public resistance and efforts by some states to ban vaccine mandates. The FDA’s full approval for the Pfizer vaccine was seen by health officials as a key step to convince hesitant individuals to get the shot and encourage employers to mandate it.

Just over half of employees had a favorable view of employers requiring Covid-19 vaccinations, while nearly two in seven strongly opposed such measures according to a July Gallup poll.

Vaccination is increasingly a requirement to be hired, and the Pentagon, New York City school district and others announced Monday they would begin requiring vaccinations. Walmart Inc., Tyson Foods Inc. and Uber Technologies Inc. are among companies requiring some employees to be vaccinated.

Write to Ana Rivas at ana.rivas@wsj.com