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  • Pfizer says its antiviral drug, Paxlovid, was nearly 90 percent effective at preventing severe COVID-19 symptoms when given to high-risk participants.
  • The drug interferes with the ability of certain enzymes to break down proteins, which can keep a virus from making copies of itself.
  • Clinical trial results also show Paxlovid is highly effective against SARS-CoV-2 variants of concern (VOC) as well as other types of coronaviruses.

This month, drugmaker Pfizer announced its new oral antiviral treatment significantly reduced the risk of hospitalization and death from COVID-19.

Results from the company’s phase 2 and 3 clinical trials found the drug, called Paxlovid, was nearly 90 percent effective at preventing severe disease symptoms when given to high-risk study participants.

The drug was so effective in early research that the trial was stopped so the data could be submitted to the Food and Drug Administration (FDA) for emergency use authorization.

The Paxlovid trial included more than 1,200 participants with a coronavirus infection at higher risk of developing severe COVID-19.

The findings, which are not yet peer reviewed, show that participants who took Paxlovid were much less likely to be hospitalized than participants who received placebo pills.

Critically, no participant given the antiviral pill died, but 10 who received placebo pills did, according to results summarized in Pfizer’s press release.

“Today’s news is a real game-changer in the global efforts to halt the devastation of this pandemic,” Albert Bourla, chairman and CEO of Pfizer, said in a statement.

“These data suggest that our oral antiviral candidate, if approved or authorized by regulatory authorities, has the potential to save patients’ lives, reduce the severity of COVID-19 infections, and eliminate up to nine out of ten hospitalizations,” he said.

While the drug worked well in clinical trials, Dr. Eric Cioe-Peña, director of global health at Northwell Health in New Hyde Park, New York, told Healthline “real life” is different.

“Trials are never exactly resembling real life data,” he said, “especially in oral medications where real-life use may include missed doses, and so forth.”

According to Pfizer, Paxlovid is a specifically designed SARS-CoV-2-3CL protease inhibitor. This means the drug interferes with the ability of certain enzymes to break down proteins, which can keep the coronavirus from making copies of itself.

“Antiviral drugs are drugs that inhibit virus’s ability to infect or replicate inside our cells,” Cioe-Peña said.

He explained that this type of drug can slow a virus’s ability to replicate and allows our immune system to “catch up” before we experience serious effects.

Pfizer also said that upon successful completion of the remainder of its clinical development program and “subject to approval or authorization,” the antiviral drug could be prescribed more broadly as an at-home treatment to not only reduce risk of severe illness, but also reduce risk of infection in adults following exposure to the coronavirus.

Clinical trial results also show Paxlovid is highly effective against SARS-CoV-2 variants of concern (VOC) as well as other types of coronaviruses.

According to Dr. Robert Glatter, an emergency physician at Lenox Hill Hospital in New York, this finding is “quite significant.”

“[It] offers those at highest risk for progression to severe disease another way to reduce the progression to severe disease hospitalization or dying, especially in those with advanced systemic disease, post-transplant or cancer, who may not mount adequate antibody responses post COVID-19 vaccination,” he said.

Glatter explained that Paxlovid is a combination of a novel protease inhibitor and a co-drug called ritonavir (an antiviral to treat HIV) that’s used to slow absorption and increase the drug’s duration of action.

“It works to block replication of the virus by inhibiting the action of critical proteases that cleave RNA,” Glatter said. “Data indicates that it’s 50 percent effective in reducing the risk of death and hospitalization if taken within 5 days of symptom onset.”

Glatter added that protease inhibitors could have side effects, which include nausea, vomiting, and diarrhea.

On Nov. 4, the United Kingdom announced approval of Merck’s oral COVID-19 treatment called Lagevrio (molnupiravir).

“Molnupiravir has been authorized for use in people who have mild to moderate COVID-19 and at least one risk factor for developing severe illness,” reads the press release. “Such risk factors include obesity, older age (>60 years), diabetes mellitus, or heart disease.”

According to Glatter, Merck’s new drug is actually an influenza drug that was repurposed to treat COVID-19.

He said one difference is that it’s not given with a co-drug, like Paxlovid, to increase the duration of action.

“It’s [molnupiravir] a nucleoside analog, which may increase the risk of DNA mutations from developing,” he cautioned, “while Pfizer’s drug, Paxlovid, which inhibits the protease Mpro, is not known to be mutagenic.”

However, Glatter confirmed that both drugs are active against coronavirus variants of concern based on current data.

Glatter pointed out that these drugs rely on early disease detection for their effectiveness.

He warned that absent an adequate supply of accurate — and widely available — rapid tests allowing for quicker disease detection, “it will do no good if people need to endure prolonged waiting times after onset of symptoms before they begin such antiviral therapies.”

Glatter noted another important issue is whether these antivirals will be able to reduce COVID-19 transmission as opposed to just disease progression.

As promising as the new antiviral treatments seem, experts say they’re not the way we’ll get past the pandemic.

“By itself, the drug will not end the pandemic,” Glatter said. “Rather, under ideal conditions, the key to ending it is through vaccination of at least 80 percent of the global population to achieve herd immunity.”

However, Glatter believes this is unlikely to occur.

“A more realistic scenario is that COVID-19 will become endemic, with ongoing local outbreaks mainly among the unvaccinated,” he said. “An annual vaccination against COVID-19 may be essential in the years ahead.”

Pfizer announced promising results for its antiviral COVID-19 treatment, with clinical trials showing the drug nearly 90 percent effective at preventing hospitalization and deaths from COVID-19.

Experts say while the results are promising, without adequate supplies of rapid tests for COVID-19, these drugs won’t be used effectively.

They also emphasize that COVID-19 antiviral drugs aren’t the way we’ll end the COVID-19 pandemic.

Rather, vaccinating at least 80 percent of the population will end the pandemic.