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High failure rate of ChAdOx1-nCoV19 immunization against asymptomatic infection in healthcare workers during a Delta variant surge.

Rajat UjjainiyaAkansha TyagiViren SardanaSalwa NaushinNitin BhathejaKartik KumarJoydeb BarmanSatyartha PrakashRintu KutumAkash Kumar BhaskarPrateek SinghKumardeep ChaudharyMenka LoombaYukti KhannaChestha WalechaRizwan AhmedAshutosh YadavArchana BajajGaurav MalikSahar QureshiSwati WaghdhareSamreen SiddiquiKamal Krishan TrehanManju ManiRajiv DangPoonam DasPankaj DougallMonica MahajanSudipta SonarKamini JakharReema KumarMahima TiwariShailendra ManiSankar BhattacharyyaSandeep BudhirajaAnurag AgrawalDebasis DashSujeet JhaShantanu Sengupta
Published in: Nature communications (2022)
Immunization is expected to confer protection against infection and severe disease for vaccines while reducing risks to unimmunized populations by inhibiting transmission. Here, based on serial serological studies of an observational cohort of healthcare workers, we show that during a Severe Acute Respiratory Syndrome -Coronavirus 2 Delta-variant outbreak in Delhi, 25.3% (95% Confidence Interval 16.9-35.2) of previously uninfected, ChAdOx1-nCoV19 double vaccinated, healthcare workers were infected within less than two months, based on serology. Induction of anti-spike response was similar between groups with breakthrough infection (541 U/ml, Inter Quartile Range 374) and without (342 U/ml, Inter Quartile Range 497), as was the induction of neutralization activity to wildtype. This was not vaccine failure since vaccine effectiveness estimate based on infection rates in an unvaccinated cohort were about 70% and most infections were asymptomatic. We find that while ChAdOx1-nCoV19 vaccination remains effective in preventing severe infections, it is unlikely to be completely able to block transmission and provide herd immunity.
Keyphrases
  • respiratory syndrome coronavirus
  • randomized controlled trial
  • coronavirus disease
  • risk assessment
  • human health