Shares of the major Covid vaccine makers fell on Monday, as the unprecedented wave of omicron infections eased, with new cases rapidly dropping across the country.

Moderna plunged more than 12%, the biggest decline in the S&P 500 as of midafternoon Monday. Pfizer was down more than 2% and its partner BioNTech slid 9%, while Novavax was off more than 10% and Johnson & Johnson fell over 1%.

White House chief medical advisor Dr. Anthony Fauci told The Financial Times last week that the U.S. is exiting the “full-blown pandemic phase of Covid-19.”

The U.S. reported a seven-day average of about 175,000 new Covid cases per day as of Sunday, according to data compiled by Johns Hopkins University, down 42% over the past week. Reported cases hit a pandemic high of more than 800,000 per day, on average, on Jan. 15.

Moderna’s Covid vaccine is the company’s only commercial product, so its stock could be exposed to further declines as demand for vaccines ebbs.

About 64% of the U.S. population is fully vaccinated with two shots of the Pfizer or Moderna vaccines or one dose of Johnson & Johnson, Centers for Disease Control and Prevention data shows.

While shots are still going into Americans’ arms, the national vaccination rate itself is rising much more slowly than earlier in the pandemic.

It took just over two months for the share of fully vaccinated Americans to go from 40% to 50% last summer and then another four months to reach the 60% level. It has gone up only four percentage points since Dec. 6.

Covid vaccinations spiked in December as states confirmed their first cases of the omicron variant, but have since fallen off. The U.S. administered an average of 443,000 shots per day over the last week, according to the latest CDC data available as of Feb. 8, down from a December high of more than 1.7 million shots per day and peak levels of nearly 3.5 million shots per day in April.

The Food and Drug Administration on Friday delayed plans to fast track authorization of the Pfizer and BioNTech’s Covid vaccine for children under 5 year old. The FDA had originally planned to authorize the first two doses of what will ultimately be a three-dose vaccine as soon as this month. However, Pfizer and the FDA said they now plan to wait until data is submitted on the third dose in April.

Pfizer and BioNTech also are developing a Covid vaccine that targets the omicron variant. CEO Albert Bourla has said the omicron shot will be ready in March, though its unclear whether a new vaccine will be needed if cases continue to decline. Moderna also has started clinical trials on an omicron-specific booster shot.

Novavax’s vaccine has not received FDA authorization. In the event that public health conditions continue to improve, it’s unclear how much demand there will be in the U.S. for the company’s vaccine after Novavax receives the regulatory green light.

In related news, Moderna CEO Stephane Bancel sold 19,000 company shares last week, totaling $2.9 million and deleted his Twitter account after two years of inactivity, raising questions on the social media platform. Bancel sells the same amount of shares on a weekly basis, according to securities filings.