Today, we’re talking about the long-awaited COVID pill.

Since the earliest days of the pandemic, researchers have been searching for an antiviral drug that could easily treat the coronavirus. Now, we may finally have it in the form of molnupiravir—a pill that appears to cut the risk of hospitalization and death due to COVID-19 by 50%.

The pill is produced by the drugmaker Merck, which released results from its trials last Friday to great excitement (and a sharp uptick in stock price), with some calling it a “game changer.” While therapies for COVID-19 already exist, they must be administered in hospitals or clinical settings through an IV drip. Molnupiravir, a pill meant to be taken twice a day for five days, would make it possible to treat people at home.

If Merck’s results hold up to peer review and the drug receives FDA approval, molnupiravir will probably make handling COVID-19 more manageable from a public health perspective. But for practical reasons, including the need for testing and cost, the pill is not a silver bullet. It won’t change the urgent need for widespread vaccination and other public health measures meant to prevent infection.

Namandjé Bumpus, a professor and director of the Department of Pharmacology and Molecular Sciences at the Johns Hopkins University School of Medicine, told me that molnupiravir is an “important addition to the toolbox” and could lead to fewer hospitalizations and deaths. However, vaccination is “still our most powerful tool in combatting the pandemic” because it prevents people from getting sick in the first place, she added.

One of the most promising things about molnupiravir is its potential to prevent severe illness—thereby preventing more deaths and keeping people out of already overburdened hospitals. One catch is that treatment needs to start early: in Merck’s trials, it began within five days of first symptoms. In the real world, this would mean that a person who starts feeling ill at home would need to be tested for COVID-19 as soon as possible because a positive test result will most likely be needed in order to get a prescription for molnupiravir. That’s easier said than done, given the lack of accessible and widespread testing in many parts of the country, not to mention long wait times for PCR test results. If people can’t confirm their COVID-19 cases early, then the availability of molnupiravir may be moot.

“With any treatment there is a window of time where it will work best,” said Bumpus. “We need to learn more about this drug and how it might work in the general population outside of a clinical trial setting, but a limitation could be that after a certain point of disease progression it won't work as well.” Promisingly, on Wednesday the Biden administration pledged $1 billion for at-home COVID-19 tests, which by December is poised to make 200 million tests available each month, and even more after that.

Concerns have also been raised about the price of molnupiravir, which, at about $700 per course, will be unaffordable for some nations. The Biden administration has already purchased 1.7 million courses from Merck for $1.2 billion—a price representing a 40x markup, as the Intercept pointed out. Merck has said that in other countries it will price the drug differently depending on national income and is planning to make generic versions available.

It makes sense to be cautiously optimistic about the drug, but there is much left to learn about the drug’s side effects, its effect on vaccinated people and pregnant people, and patient adherence to a five-day course. And, noted Bumpus, “even with treatment there is still a risk of progression to severe disease.” That’s why vaccination and other measures for stopping the spread of COVID-19 remain crucial. “We will not be able to rely on treatment of COVID-19 alone to combat the pandemic,” said Bumpus.

After trial data were released last week, stock prices for vaccine-makers like Moderna and BioNTech fell as Merck’s stock rose, suggesting a troubling either-or attitude to treatment versus vaccination (which is perhaps best illustrated by the popularity of unproven treatments like ivermectin and hydroxycholoroquine among vaccine skeptics). If molnupiravir receives FDA approval, it will be critical for public health authorities to send the message that treatment and vaccination are meant to work in tandem, not compete with each other, say experts.

“Treatment is an important part of the toolbox,” said Bumpus, “but vaccination is the best method we have for prevention.”