HealthDay News — For individuals who receive two doses of mRNA-1273 SARS-CoV-2 vaccine, vaccine efficacy (VE) against symptomatic COVID-19 appears to peak at 120 days after the first dose, according to a research letter published online June 8 in JAMA Network Open.

Dan-Yu Lin, PhD, from the University of North Carolina at Chapel Hill, and colleagues considered the mRNA-1273 P301 cohort study, which is an ongoing phase 3, randomized, placebo-controlled trial of 30,415 US adults evaluating the efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine. The VE against symptomatic COVID-19 was estimated at 94.1 and 93.2% in an interim analysis and at completion of the blinded phase, respectively. The per-protocol population (28,451 participants who tested negative for SARS-CoV-2 at baseline and received 2 vaccine doses by the end of the blinded phase) was included in this cohort study.

The researchers found that the placebo group included 14,164 patients with 769 cases of COVID-19, while the vaccine group included 14,287 patients with 56 cases of COVID-19. At 40 days after dose 1, VE reached 92.6% and increased to a peak of 94.1% at 120 days. At approximately 120 days, the VE started to decline and reached 89.6% at 200 days. Even at 200 days after dose 1, the level of protection was high, although there was uncertainty estimating VE near the end of blinded follow-up.

“Few cases of COVID-19 occurred after six months in our study, making it difficult to precisely estimate the degree of waning at the end of the blinded follow-up,” the authors write.

One author disclosed financial ties to Pfizer and was involved in COVID-19 vaccine research; a second author disclosed ties to Moderna.

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