Pfizer's COVID-19 pill combination, known as Paxlovid
Pfizer's COVID-19 pill combination, known as PaxlovidPfizer/Handout via REUTERS

A new study authored by researchers from the Clalit Health Fund and published in ResearchSquare contains worrying findings regarding the efficacy of Paxlovid, a drug combination developed by Pfizer to treat patients at high-risk of developing serious cases of COVID.

The study was based on 109,213 participants who were eligible for Paxlovid treatment (high-risk and with confirmed SARS-CoV-2 infection), 3,939 of whom chose to be treated with Paxlovid. While those over the age of 65 did appear to benefit from the course of treatment, those under 65 did not, and data regarding mortality even suggests that Paxlovid was detrimental to these people.

In the 65+ age group, researchers found a 67-percent reduction in hospitalization rates for those who took Paxlovid, and an 81-percent reduction in COVID mortality. These figures were notably lower than those reported by Pfizer, which claimed an 89 percent efficacy rate in its FDA submission.

In the 40-64 age bracket, a reduction of 22 percent in hospitalizations was noted, but an increase of 64 percent of mortality. The researchers described this as of “no significant benefit in avoidance of severe COVID-19 outcomes,” as “only a two-sided P value of less than 0.05 was considered to indicate statistical significance.”

The study’s authors also divided the data according to “immunity” status. Participants with no prior immunity (with one or less mRNA vaccine dose and no documented previous COVID infection) were compared with those considered immune (due to two or more vaccine doses, previous infection, or a combination).

Thus analyzed, the data revealed that all groups benefited from Paxlovid treatment, except for the 40-64 age group, where people who used Paxlovid were 18 percent more likely to be hospitalized than those who did not take the drug.

The researchers noted that Paxlovid was trialed by Pfizer during a period when the Delta strain was prevalent, and noted that the efficacy of Paxlovid against the currently prevalent Omicron variant “is unknown.”

They also noted that they were not able to monitor treatment adherence in those studied; it was thus possible that people listed as taking Paxlovid did not complete the five-day course of treatment. In addition, the analysis did not allow for treatment bias in that people with worse symptoms were presumably more likely to agree to take Paxlovid. However, they added, it is uncertain whether this factor would lead to an underestimation or overestimation of the efficacy of Paxlovid.