New York CNN Business  — 

Shares of drug giant Pfizer surged nearly 11% Friday after the company announced positive test results for an experimental pill it has developed to fight Covid-19.

Pfizer (PFE) said the pill reduced the risk of hospitalization and death for high-risk patients who were part of a trial taking the drug.

The news comes just a few days after Pfizer reported strong earnings and sales, thanks largely to the success of the Covid-19 vaccine it developed with BioNTech (BNTX).

The US Food and Drug Administration also recently approved the use of the Pfizer-BioNTech vaccine in 5- to 11-year-old children.

But shares of BioNTech, which will report earnings next week, plunged more than 20% Friday. Shares of Pfizer’s Big Pharma rival Merck (MRK), which also is developing a Covid pill, were down about 10%.

Biotech Novavax (NVAX), which is applying for emergency use authorization of its Covid vaccine, fell more than 11%.

Moderna (MRNA), another biotech that has its own Covid-19 vaccine, plummeted about 17% Friday.

That follows a nearly 18% slide for the stock Thursday after Moderna announced weaker than expected results and a disappointing outlook due to production and shipment problems that will delay the deliveries of its vaccine.