(Bloomberg) -- Merck & Co. shares have wiped out their gains for 2021 and are on track for their worst month in 12 years amid weakening data for its Covid-19 pill.

The stock fell as much as 4.8% on Monday, hitting a two-month low, ahead of a U.S. Food and Drug Administration advisory committee meeting on Tuesday to review results and make recommendations on the oral antiviral, molnupiravir or Lagevrio. The company has lost almost $17 billion in market value over the past two sessions due to disappointing data showing the drug cut hospitalizations and death from mild to moderate Covid by 30%, which is down from a prior analysis that had the figure at 48%. 

Wall Street analysts expect Merck’s Covid pill will get an emergency authorization regardless, though its usage may be more limited given the better safety and efficacy of Pfizer Inc.’s antiviral.   

SVB Leerink analyst Daina Graybosch expects the FDA panel will focus on the issues seen in Merck’s pill, including “risk of harm to fetuses and accelerated viral mutation rate that may drive emergence of new SARS-CoV-2 variants, in addition to relatively weaker efficacy,” she wrote in a research note. 

Demand for antivirals for the profitable government stockpiles will shift to Pfizer over time, she said. Merck is down 14% so far in November and on pace for its worst month since 2009, while Pfizer, which makes one of the world’s best-selling Covid vaccines, is up 25% and poised for its best month in 30 years.

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