First and second doses of Covishield vaccine provided high level of protection against SARS-CoV-2 infection in highly transmissible settings: results from a prospective cohort of participants residing in congregate facilities in India

ObjectivesThis study aimed to determine the effectiveness of Covishield vaccine among residents of congregate residential facilities.DesignA prospective cohort study in congregate residential facilities.SettingDharamshala, Himachal Pradesh, India, from December 2020 to July 2021.ParticipantsResidents of all ages in seven facilities—three monasteries, two old age homes and two learning centres—were enrolled.ExposuresFirst and second doses of Covishield vaccine against SARS-CoV-2 infection.Main outcomes measuresPrimary outcome was development of COVID-19. Secondary outcome was unfavourable outcomes, defined as a composite of shortness of breath, hospitalisation or death. Vaccine effectiveness (%) was calculated as (1−HR)×100.ResultsThere were 1114 residents (median age 31 years) participating in the study, 82% males. Twenty-eight per cent (n=308/1114) were unvaccinated, 50% (n=554/1114) had received one dose and 23% (n=252/1114) had received two doses of Covishield. The point prevalence of COVID-19 for the facilities ranged from 11% to 57%. Incidence rates (95% CI) of COVID-19 were 76 (63 to 90)/1000 person-months in the unvaccinated, 25 (18 to 35)/1000 person-months in recipients of one dose and 9 (4 to 19)/1000 person-months in recipients of two doses. The effectiveness of first and second doses of Covishield were 71% (adjusted HR (aHR) 0.29; 95% CI 0.18 to 0.46; p