The fall COVID-19 vaccine season is starting slowly for Pfizer, with American sales of its Comirnaty shots sinking 25 percent after federal regulators narrowed recommendations on who should get them.

Approval of updated shots also came several weeks later than usual, and Pfizer said that hurt sales as well.

Many Americans get vaccinations in the fall, to gain protection from any disease surges in the coming winter. Researchers say interest in COVID-19 shots has been declining, and that trend could pick up this fall due to anti-vaccine sentiment and confusion about whether the shots are necessary.

The Centers for Disease Control and Prevention last month stopped recommending COVID-19 shots for anyone, instead leaving the choice up to patients. The government agency said it was adopting recommendations made by advisers picked by U.S. Health Secretary Robert F. Kennedy Jr.

Before this year, federal health officials — following the advice of infectious disease researchers — recommended annual COVID-19 boosters for all Americans ages 6 months and older. The idea was to update protection as the coronavirus evolves.

That sentiment started to shift earlier this year when Kennedy, who has questioned the safety of COVID-19 vaccines, said they were no longer recommended for healthy children and pregnant women.

Dr. Amesh Adaja said vaccine rates have been “suboptimal” in recent years even for people considered a high risk for catching a bad case of COVID-19.

“That’s only going to fall off more this season,” the senior scholar at the Johns Hopkins Center for Health Security said recently.

The shifting guidance caused some confusion in September, once updated shots began arriving at drugstores, the main place Americans go to get vaccinated. Some locations required prescriptions or started asking customers if they had a condition that made them susceptible to a bad case of COVID-19.

The change also created questions about whether insurance coverage would continue. A major industry group, America’s Health Insurance Plans, has since clarified that its members will cover the shots.

CVS Health announced earlier this month that it will not require prescriptions at its stores and clinics.

Pfizer saw U.S. Comirnaty sales drop to $870 million in the recently completed third quarter from $1.16 billion in the same time frame last year. That came after vaccine sales rose the first two quarters of the year.

Wall Street analysts also expect sales of Spikevax shots from Moderna to tumble about 50 percent in the third quarter, according to the data firm FactSet.

Moderna will report its third-quarter results today.