| U.S. health officials last week announced a plan to use $3.2 billion to develop drugs against Covid and other viruses with pandemic potential. Anthony Fauci, President Joe Biden's medical adviser on the pandemic, said these medicines could be taken at home after a person is already sick, comparing them to flu-fighting Tamiflu. Tamiflu is one of the most recognizable antiviral drugs in the world and was wildly popular in 2009 during a milder swine flu pandemic. But the medicine fell out of favor when providers realized its benefits for most sick patients were limited and cases emerged of the virus developing resistance to the drug. Experts warn a future Covid-19 antiviral could face the same pitfalls.  Tamiflu capsules Photographer: Matthew Baker/PA Images Tamiflu, otherwise known as oseltamivir, was developed by Roche Holding, approved in the U.S. in 1999, and has been available as a generic since 2016. Regulators including the U.S. Food and Drug Administration approved the drug based on a rigorous review of its trials, Roche said, and the World Health Organization and other public authorities recommend it in their guidelines for flu treatment and prevention. Antivirals like Tamiflu target virus replication, which means they can stop the virus from multiplying further but can't cure the infection already in the body. As a result, the drugs have to be taken as soon as possible –– Tamiflu should be taken within the first 48 hours of infection, for example. "It's like trying to get in front of a runaway train," says Stephanie DeWitte-Orr, a virologist at Wilfrid Laurier University in Waterloo, Ontario. "You can hold onto the back and slow it down, but to stop it fully in its tracks would be very difficult." If taken early, Tamiflu can shorten the duration of infection one to two days. That might be critical for high-risk patients but "perhaps not that meaningful" for the average sick person, says William Schaffner, an infectious disease expert from Vanderbilt University. Still, antivirals could benefit immunocompromised people like those with transplants and some cancer patients for whom vaccines may not be as effective. Combinations of antiviral drugs have seen great success in keeping the HIV virus at bay. Some Covid antiviral treatments, like monoclonal antibodies and Gilead Sciences' remdesivir, appear to be effective, but must be given intravenously. Scientists hope to develop a cheaper, oral alternative to treat Covid, but antivirals will never be a replacement for vaccines, Schaffner says. "Treatments, as good as they might be, are always imperfect," he says. "Why risk that when you can prevent the disease on the front end?"—Rebecca Torrence | 
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