A study yesterday in JAMA suggests Paxlovid, the oral antiviral approved for use against severe COVID-19 symptoms, did little to lessen the risk of hospitalizations and death among older, vaccinated adults in Canada.
Pfizer’s initial clinical trials on the drug were conducted on unvaccinated adults, the authors said, with median ages of 42 to 46 years. Older adults are more likely than younger adults to be vaccinated against COVID-19 and are at the greatest risk of severe complications from the virus.
The study looked at all-cause mortality and all-cause hospitalizations in adults in Ontario, Canada. Between April 1 and November 30, 2022, Ontario implemented an age-restrictive policy on access to Paxlovid, with only those 70 and older able to get the drug.
“Since the strongest predictor of severe COVID-19 is advanced age, it has been crucial to obtain evidence on whether the results of the Pfizer trials generalized to older and vaccinated populations,” said John Mafi, MD the study’s lead author in a press release from the Univeristy of California Los Angeles.
The authors compared outcomes among adults just under 70 years who were not prescribed Paxlovid to those who were given the antiviral. The authors identified 1,620,884 Ontarians aged 65 to 74 years during the study period; most (87.5%) received at least 2 COVID-19 vaccines.
Paxlovid’s effect 4 times weaker than in clinical trial
Overall, the authors found the prescription rate of Paxlovid more than doubled after the age-based policy was put in place, increasing by 118% at age 70.
But the increased use of Paxlovid did not result in fewer hospitalizations or deaths for those treated with the medicine.
There were no significant differences just below compared with just above age 70 years (per 10,000 patients per month) in COVID-19-related hospitalizations (39.5 vs 42.9) or all-cause mortality (109.6 vs 115.7).
The authors said the study showed Paxlovid’s effect on COVID-19 hospitalization among vaccinated older adults is four times weaker than the effect originally reported in Pfizer’s 2022 clinical trial, reducing hospitalizations by 1.3 percentage points. The original clinical trial showed an absolute risk reduction of 5.5 percentage points against hospitalizations.
“Since the study found no significant effect on COVID-19 hospitalizations and deaths among vaccinated older adults, our findings underscore the urgent need for further randomized-clinical trials investigating Paxlovid’s effects in higher-risk populations, such as older subgroups who are frail or immunosuppressed,” Katherine Kahn, MD, another study author.
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