| If you come down with influenza, there's a good chance your doctor will immediately prescribe a five-day course of the antiviral pill oseltamivir in order to shorten the course of illness.
Now Pfizer is trying to see if something similar can be done for the coronavirus. It's recently begun human safety trials of a new pill that could be given at the first sign of a coronavirus infection, to prevent it from becoming severe.
"This is really a potential game-changer," said Mikael Dolsten, Pfizer's chief scientific officer, in an interview with Bloomberg News.
Antiviral pills are sorely needed for Covid-19. While vaccines can prevent most cases, it could take years to get shots to the whole world. Some people will refuse vaccinations, and the virus will continue to mutate in the meantime. Meanwhile, the main drugs now for treating early Covid-19 are antibodies that must be infused at a medical facility. That's created logistical challenges that have hampered use. Pills would be so much easier.  Scientists at Merck are researching new ways to treat Covid-19, including the antiviral pill molnupiravir. Photographer: Christopher Leaman for Bloomberg Businessweek The Pfizer pill is a protease inhibitor; it blocks a crucial viral enzyme needed for replication. If that name sounds vaguely familiar, that's because other protease-inhibitor drugs have for years been used to treat HIV and hepatitis C. And because the protease is an internal enzyme, it should be less prone to mutation than surface proteins targeted by antibodies, Pfizer says.
While the research is only in the beginning stages, Dolsten says the company hopes to get safety results within weeks, and could begin large-scale efficacy tests early in the second quarter. If it works, Pfizer says the drug might be given twice a day for about five days.
Pfizer isn't the only big drugmaker with a potential Covid-19 pill. Merck and its partner Ridgeback Biotherapeutics are in late-stage tests of molnupiravir, a potential Covid-19 pill that works through a different mechanism. If both pills succeed, that would be great news indeed for keeping Covid-19 under control in the long term.—Robert Langreth | 
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