Pfizer Says Its COVID-19 Pill Will Be Effective Against Omicron. How Does It Work?

Since the Omicron variant prompted concerns among public health authorities, major vaccine manufacturers have announced their coronavirus defense plans.

Pfizer’s CEO Albert Bourla told CNBC that the company’s antiviral pill, Paxlovid, which boasts an 89% effectiveness in reducing COVID-19 hospitalizations and deaths, should remain effective against Omicron.

The company submitted an application to the Food and Drug Administration (FDA) for emergency use authorization of the pill on November 16.

Some scientists are worried that Omicron’s mutations could make it partially resistant to current COVID-19 vaccines, raising the question of whether an extra tool is needed in the line of coronavirus defense.

Both Pfizer and Moderna have announced plans for a potential Omicron-specific vaccine, should that be necessary. Pfizer, Moderna, and Johnson & Johnson are all currently testing their vaccine efficacies against the Omicron variant. It will take at least two weeks for scientists to find out more about the variant.

How Does Pfizer’s Antiviral Pill Work?

While vaccines prevent infection, Pfizer’s Paxlovid works by trying to fight off the virus if a person has already been diagnosed with COVID-19. 

Paxlovid falls into a category of drugs called protease inhibitors, which block the protease enzyme that’s responsible for packaging and multiplying a virus in the body. This is similar to pre-exposure prophylaxis (PrEP), a treatment for the human immunodeficiency virus (HIV).

“The way this drug works is it slows down the lifecycle of the virus so that we’re making smaller numbers of new [virus] particles, which means we get a slower spread in the body of the virus, and therefore more time for the immune system to kick in,” Jason Diaz, PhD, a virology expert at LaSalle University, told Verywell.

In contrast, the COVID-19 vaccines teach the body how to target the virus’s spike protein, which is responsible for gaining entry to and infecting human cells.

“If we can block the very start, that’s the most efficient way to kill viruses.” Diaz said. “We care a lot about the spike protein because that’s really what’s going to help determine how transmissible the virus is going to be, and how infectious it is going to be.”

More than 30 out of 50 mutations are in Omicron’s spike protein, which may affect vaccine efficacies. But there's only one mutation in the 3CL protease, an enzyme targeted by Pfizer’s antiviral pill.

“There’s no reason for us to believe that the drug isn’t going to work well for this particular virus,” Diaz said.

He added that Paxlovid should be most effective when people take it as soon as they have symptoms. Pfizer proposed the pill as an at-home treatment to avoid severe illness. People would still need to rely on COVID-19 testing so that they can take the pill at the onset of an infection, he said.

“All the antivirals being developed, including the Pfizer one, are really only going to be effective if you have robust testing,” Diaz added. “You don’t want to wait for them to get to the hospital.”

Antiviral Pills Can’t Stop Virus Mutations

While Pfizer’s antiviral pill may slow the virus from replicating inside an infected person, it doesn’t stop the virus from mutating.

The pill targets the protease enzyme, but not the polymerase enzyme, which controls genetic material and leads to mutations.

“There’s no reason for me to believe that this drug would slow down the mutation rate, but it should slow down the infection rate in a person so that they can recover quickly and not have to be hospitalized,” Diaz said.

Researchers are still trying to determine how effective the current COVID-19 vaccines are against the Omicron variant. Currently, the Pfizer vaccine is 88% effective against COVID-19 hospitalization while the Moderna vaccine is at 93%, according to a recent study by the Centers for Disease Control and Prevention.

The FDA has yet to authorize Pfizer’s pill. With what we know, vaccines remain incredibly powerful at reducing infection and bringing us closer to the end of the pandemic, Diaz said.

He added that he’s excited about the drug’s potential, so long as it’s used to complement—not replace—existing public health measures.

“Try to not get sucked into thinking of having a ‘single magic bullet’ for COVID,” Diaz said. “We need things like social distancing, and masking, and vaccines, and these drugs to get to a point where this is no longer playing such a strain on our healthcare system, and where we can go back to whatever the ‘new version of normal’ looks like.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.