(Bloomberg) -- For the world’s leading Covid-19 vaccine makers, news that Merck & Co.’s experimental pill cuts the risk of hospitalization and death in half was the latest blow in a very bad week.

Stocks including Moderna Inc. and BioNTech SE have shed about $84 billion in combined value this week in the aftermath of a stock market slump that sent the two companies to their lowest level since July. 

Selling accelerated on Friday, with BioNTech and Moderna each declining as much as 16% in New York as Merck delivered the news on its experimental pill that Wall Street called a “game changer.” The drug, called molnupiravir, reduced the risk of hospitalization or death by 50% in a study, raising concerns about the long-term revenues for companies providing inoculations.

“You have news of a new player coming into the market with a much less rigorous treatment and that alone has to dampen the day for the rest of the field whether they’re vaccines or drugs administered in the hospital for Covid-19,” said Jared Holz, managing director of healthcare equities at Oppenheimer & Co. “The vaccine revenue numbers over the next few years would have to come down.”

Wall Street analysts had forecast Moderna’s Covid-19 vaccines will bring in more than $20 billion in sales this year, before dropping to $6.1 billion by 2025.

Not Over Yet

In spite of this week’s selloff, vaccine stocks remain among biotech’s top performers since the start of the pandemic. Moderna shares are up 1,590% since the start of 2020, while BioNTech and peer Novavax Inc. have seen similarly eye-popping gains of 600% and 4,000%, respectively. 

Not all investors see Merck’s Covid-19 breakthrough as a reason to shun all vaccine makers. The pandemic is far from over, argues Brad Loncar, chief executive officer of Loncar Investments.

“Time and time again we’ve seen that a quick take to positive news thinking that this means the pandemic is over has been wrong every single time,” he said by phone. “I don’t think this is going to hurt the vaccine companies as much as maybe a quick reaction would infer.”

Selling spread beyond vaccine stocks and biotechnology companies. Companies that have developed or are working on antibody treatments for Covid-19 and closely-watched exchange-traded funds like the iShares Biotechnology ETF, also fell. 

Here’s how some of them performed on Friday:

  • BioNTech and Moderna each crashed as much as 16% to the lowest since July
  • Novavax tumbled as much as 26% while vaccine peers sank: CureVac -16%, Arcturus Therapeutics -10%, Inovio Pharmaceuticals Inc. -8.9%
  • Companies with antibody treatments for Covid: Adagio Therapeutics Inc. -42%, Vir Biotechnology Inc. -24%, AbCellera Biologics Inc. -14%, Regeneron Pharmaceuticals Inc. -8.1%
  • iShares Biotechnology ETF falls as much as 4.1%, the most since late March

The broader health-care sector fell four the fifth time in the past six sessions Friday, with life sciences toolmakers and medical device companies underperforming the broader market. The S&P 500 Health Care Index’s 5% drop this week is the group’s worst week since October 2020.

©2021 Bloomberg L.P.