(HealthDay News) — Vaccine effectiveness against symptomatic COVID-19 decreases by 20 weeks after the second dose of BNT162b2 or CHAdOx1-S, but limited waning is seen against COVID-19-related hospitalization and death, according to a study published online in the New England Journal of Medicine.

Nick Andrews, PhD, from the United Kingdom Health Security Agency in London, and colleagues used a test-negative and case-control design to estimate vaccine effectiveness against symptomatic COVID-19 and related hospitalization and death in England. The effectiveness of the ChAdOx1-S and BNT162b2 vaccines was assessed over time since receipt of the second vaccine dose for the B.1.1.7 (alpha) and B.1.617.2 (delta) variants.

The researchers found that in the early weeks after receipt of the second dose, vaccine effectiveness against symptomatic COVID-19 with the delta variant peaked and then decreased to 44.3 and 66.3% with the ChAdOx1-S and BNT162b2 vaccines, respectively, by 20 weeks. Compared with those aged 40 to 64 years, persons aged 65 years or older had greater waning of vaccine effectiveness. At 20 weeks or more after vaccination, vaccine effectiveness decreased less against hospitalization (to 80.0 and 91.7%, respectively, with ChAdOx1-S and BNT162b2) and death (to 84.8 and 91.9%, respectively, with ChAdOx1-S and BNT162b2). Compared with healthy adults, persons aged 65 years or older in a clinically extremely vulnerable group and persons aged 40 to 64 years with underlying medical conditions had greater waning in vaccine effectiveness against hospitalization.

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“Our study showed evidence of significant waning of vaccine effectiveness against symptomatic disease, but with limited waning against severe disease, for at least five months after an extended-interval, 2-dose schedule with the ChAdOx1-S and BNT162b2 vaccines,” the authors write.

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