Older patients treated with nirmatrelvir boosted by ritonavir (Paxlovid) for COVID-19 had lower rates of hospitalization and death compared with those not treated with the antiviral during the Omicron wave, according to an observational retrospective cohort study from Israel.

Among patients ages 65 and older, the rate of hospitalization due to COVID was 14.7 cases per 100,000 person-days for the 2,484 patients who received nirmatrelvir compared with 58.9 cases per 100,000 person-days for the 40,337 untreated patients (adjusted HR 0.27, 95% CI 0.15-0.49), reported Ronen Arbel, PhD, of Clalit Health Services in Tel Aviv, and colleagues.

Death occurred in two nirmatrelvir-treated patients and in 158 untreated patients (aHR 0.21, 95% CI 0.05-0.82), they said in the New England Journal of Medicine.

For patients ages 40 to 64, the rate of hospitalization was 15.2 cases per 100,000 person-days among treated patients and 15.8 cases per 100,000 person-days among untreated patients (aHR 0.74, 95% CI 0.35-1.58). Deaths were similar for this age group as well (aHR 1.32, 95% CI 0.16-10.75).

“Our results conform to CDC guidelines to treat high-risk patients, prioritizing those above 65,” Arbel told MedPage Today in an email. “No evidence of benefit was found in younger adults.”

However, “whether or not to give a patient nirmatrelvir is a clinical decision,” he added. “It should not be limited [to those over 65], but rather a factor to consider in the risk assessment of patients based on their risk profile and additional clinical considerations, including symptoms.”

In addition, the study found that older patients who had immunity either from vaccination or previous infection also had better outcomes. Hospitalization was required in 1% of those with immunity (505 of 39,503) compared with 8% (277 of 3,318) who had no immunity.

Arbel and co-authors designed this study to evaluate the effectiveness of nirmatrelvir in a vaccinated population during the Omicron wave to compare their results with that of the EPIC-HR trial, which showed an 89% reduced risk of progression to severe disease with nirmatrelvir compared with placebo during the Delta wave.

“We expected that the results would differ from the randomized controlled trial since the risk of severe disease is much lower in Omicron,” Arbel said.

In addition, the two study populations were different, “as the vast majority of our patients were vaccinated,” he explained. “In the subgroup of unvaccinated patients over 65 years, we saw comparable results to the randomized controlled trial.”

For this study, Arbel and team included all members of Clalit Health Services ages 40 and older at the start of the study period, who were eligible to receive nirmatrelvir. A total of 109,254 patients met the eligibility criteria, of whom 3,902 received nirmatrelvir during the study period (Jan. 9 to March 31, 2022). Mean age was 60 years, 39% were 65 and older, and 60% were women.

Treatment was given a mean 2 days after a positive test (range 1 to 5 days), and 97% completed the 5-day course of nirmatrelvir.

More comorbidities were reported in the younger group versus the older patients, including obesity (42% vs 34%), hypertension (49% vs 33%), and diabetes (40% vs 26%).

“Indeed, younger patients had more comorbidities since in order to be eligible for therapy at this age, you needed to have additional risk factors for severe outcomes,” Arbel noted.

The authors acknowledged that residual confounders may have introduced bias into their study.

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