The country's first two antiviral Covid pills are here — and they could be potential game-changers for addressing the pandemic.

On Thursday, the U.S. Food and Drug Administration approved drugmaker Merck's "molnupiravir" pill, meant to treat people who are sick with Covid, for high-risk patients ages 18 or older. The moves comes a day after the FDA approved Pfizer's Covid pill, called Paxlovid, for high-risk patients ages 12 and older.

Treatments could be available within a matter of days. The Centers for Disease Control and Prevention still needs to craft nationwide guidelines for using the drugs.

Both pills come with potential concerns, including affordability for the average person. Pfizer's pill reduced hospitalizations and deaths in high-risk patients by 88% in clinical trials, while Merck's pill — which isn't recommended for people who are pregnant — only cut those rates by 30%.

But they both represent a potential turning point in the pandemic: the ability to easily treat sick patients, prevent severe illness, keep people out of the hospital and lower the country's Covid death rate.

"All the excitement around these medications is warranted," Dr. Daniel Griffin, a clinical instructor of medicine in the division of infectious disease at Columbia University Medical Center, tells CNBC Make It.

Here's how the pills work, and what they mean for potentially ending the pandemic:

Pfizer's Paxlovid

Paxlovid is a type of drug called a protease inhibitor, and is "perhaps a little more exciting," Griffin says.

When the virus replicates within a human cell, it uses an enzyme called protease — which works like scissors, chopping up strands of viral protein into small pieces so they can spread more easily. Paxlovid poisons those protease enzymes, forcing the virus to maintain "this big, long protein that is not functional," says Griffin.

When the virus can't replicate, the illness doesn't progress to a severe degree, says Dr. Judith O'Donnell, professor of infectious diseases at the Perelman School of Medicine at the University of Pennsylvania.

Patients take six pills per day — four Paxlovid pills, and two pills of a common HIV drug called ritonavir — for five days. The ritonavir acts as a booster to help Paxlovid "be in the body, remain active and do its job longer," O'Donnell says.

According to Pfizer's clinical trial data, Paxlovid and ritonavir reduce the risk of hospitalization or death in high-risk patients by 89%.

Last month, Pfizer announced that it'll use a tiered pricing approach for the pill, scaling the drug's cost based on a country's income level. The drugmaker also said that it'll allow generic drug manufacturers to produce Paxlovid in 95 low- and middle-income countries.

Pfizer reportedly expects to manufacture enough Paxlovid to treat 180,000 people by the end of the year, and at least 50 million people by the end of 2022.

Merck's molnupiravir

Merck's Covid pill isn't exactly new: It was initially developed in the early 2000s to treat influenza.

When the pandemic hit, scientists pivoted to see if molnupiravir could work on SARS-CoV-2, the virus that causes Covid, O'Donnell says.

Once the virus enters a human cell, it duplicates its RNA to replicate and spread throughout the body. Merck's antiviral drug mimics parts of that RNA, purposefully making mistakes in the virus' genetic code that cause it to mutate itself into extinction.

People experience "the height of viral replication" when they first start experiencing Covid symptoms, Griffin says, meaning Merck's pill is most effective when taken within a week of testing positive.

Patients take eight pills a day for five days. Last month, Merck announced that upon FDA approval, the U.S. government would spend roughly $2.2 billion on enough doses of molnupiravir for 3.1 million courses of treatment.

That means each treatment would cost the U.S. $700 to purchase — no small fee, but cheaper and easier to deploy than an intravenous drug like remdesivir, which costs $3,000.

"There's already a lot of groundwork being set up so that these drugs can very quickly be distributed," Griffin says.

What these drugs mean for ending the pandemic

Either pill could potentially turn Covid into an easily treatable disease, rather than one that lands you in the hospital.

"If they can prevent hospitalization, that makes a huge difference to me here in the trenches," O'Donnell says.

Both drugs' trials focused on unvaccinated people, who are roughly 29 times more likely than fully vaccinated people to be hospitalized with Covid, according to a CDC study from August. If you're fully vaccinated and boosted against Covid, you're highly unlikely to experience severe symptoms if you get sick.

Regardless of the pills' approval status, experts say unvaccinated people should still get vaccinated — and then boosted, once eligible. It's far more important to prevent infections than it is to treat the disease, Dr. Anthony Fauci said during a White House briefing last month.

Vaccines prevent transmission of the virus, which could lead to more dangerous Covid mutations in the future.

Update: This story has been updated to reflect the FDA's approval of Merck's molnupiravir and Pfizer's Paxlovid antiviral Covid pills.

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