Filled vials exiting the vial capping machine, Merck

Courtesy of Merck

Vaccine stocks were still sliding Wednesday, four days after U.S. drug giant Merck said its Covid-19 antiviral pills cut hospitalization or death by approximately 50%.

Investors received Merck’s (ticker:MRK) news with rotund optimism, buoyed by the prospect of a pandemic panacea. But that same optimism has prompted markets to pull back from vaccine stocks that were otherwise coasting steadily higher.

BioNTech (BNTX) stock slipped close to 3.2% in early market trading Wednesday, even after CEO Uğur Şahin said updated Covid vaccines may be needed next year to combat disease mutations. Shares of the company have fallen 11.9% since Merck’s announcement.

Moderna (MRNA) stock fell 4% Wednesday morning, and has dropped 17% in total since last Thursday. Merck’s (MRK) Friday announcement overshadowed any gains the stock made following the news that the Food and Drug Administration was likely to authorize a booster dose of Moderna’s vaccine.

Novavax (NVAX) fell 3.4% on Wednesday. The company appointed three new executives to oversee vaccine safety and development Tuesday, but has yet to announce it is ready to submit its coronavirus vaccine to the Food and Drug Administration for emergency use authorization, which may have further irked investors.

Shares of Novavax traded at $165.14 Wednesday, a 20% decrease from last Thursday’s close at $207.11.

Some analysts believe the market’s reaction to Merck’s positive data may have been overblown. For one, the antiviral pill may not be the silver bullet that investors hoped for on Friday. Scientists have warned that the way Merck’s antiviral pill works could lead to cancer or birth defects.

Vaccine stocks may get a lift if governments in Europe and the U.S. choose to “over boost,” or choose to impose broader recommendations for booster shots, to avoid a potential winter wave, said SVB Leerink analyst Geoffrey Porges in a Wednesday research note. Of the vaccines currently available, Moderna and Pfizer (PFE) are likely to continue dominating developed market share until at least mid-2022.

Demand for vaccines remains high, especially in emerging markets that have low vaccine rates, wrote Shilan Shah, Capital Economics senior economics. Shah foresees vaccination efforts in South and South East Asia and Sub-Saaharan Africa ramping up as China, the U.S., and other G7 countries boost vaccine exports and donations.

“A boost to supply of around 1.5bn doses from the factors listed above would be enough to fully vaccinate almost a third of the entire population of SSA, South Asia (excluding India) and South East Asia,” Shar wrote.

Low and middle-income countries may be a promising market opportunity for protein-based vaccines that do not require complex cold chain infrastructure, such as the ones being developed by Novavax and French company Valneva (VALN).

Write to Sabrina Escobar at sabrina.escobar@barrons.com