Effectiveness of ChAdOx1 nCoV-19 Corona Virus Vaccine (Covishield™) in preventing SARS-CoV2 infection, Chennai, Tamil Nadu, India, 2021

Abstract

Background: India experienced the second wave of the COVID-19 pandemic in March 2021, driven by the delta variant. Apprehensions around the usefulness of vaccines against delta variant posed a risk to the vaccination program. Therefore, we estimated the effectiveness of two doses of the ChAdOx1 nCoV-19 (Covishield) vaccine against COVID-19 infection among individuals ≥45 years in Chennai, India. Methods: A community-based cohort study was conducted from May to September 2021 in a selected geographic area in Chennai, Tamil Nadu. The estimated sample size was 10,232. We enumerated individuals from all eligible households and periodically updated vaccination and COVID-19 infection data. We computed vaccine effectiveness with its 95% confidence interval for two doses of the Covishield vaccine against any COVID-19 infection. Results: We enrolled 69,435 individuals, of which 21,793 were above 45 years. Two dose coverage of Covishield in the 18+ and 45+ age group was 18% and 31%, respectively. The overall incidence of COVID-19 infection was 1099 per 100,000 population. The vaccine effectiveness against COVID-19 disease in the ≥45 age group was 61.3% (95% CI: 43.6 - 73.4) at least two weeks after receiving the second dose of Covishield. Genomic analysis of 74 (28 with two doses, 15 with one dose, and 31 with zero dose) out of the 90 aliquots collected from the 303 COVID-19 positive individuals in the 45+ age group showed delta variants and their sub-lineages. Conclusion: We demonstrated the effectiveness of two doses of the ChAdOx1 vaccine against the delta variant in the general population of Chennai. We recommend similar future studies considering emerging variants and newer vaccines. Two-dose vaccine coverage could be ensured to protect against COVID-19 infection.

Perspective Chapter: Tracking Trails of SARS CoV-2 – Variants to Therapy

“…Another source of ground data is ongoing and recently completed vaccine clinical trials. ChAdOx1 nCoV-19 derived vaccine did not fare well in South Africa, where B.1.351 variant dominated, and South Africa halted its distribution in February [89,90]. ChAdOx1 nCoV-19 derived vaccine is close to filling for authorization in the US and this vaccine is already being distributed elsewhere, including in the UK, and Europe by WHO [89].…”

“…Another vaccine that was tested in South Africa is from protein subunit vaccine, this vaccine is not yet being distributed, but it is getting close to filling for authorization in the UK, the US, and elsewhere. The most recent update read out of data suggests that while the protein subunit vaccine was almost 90% effective in the UK, it was much less effective in South Africa about 49 or 55% depending on whether or not people include participants infected with HIV [74,90,91]. A vaccine made by a piece of a modified virus is now being distributed in the US, reports a similar trend.…”

“…This vaccine was 72% effective at preventing moderate to severe disease in US 28 days after vaccination. In South Africa, that number was only 64% [90]. But importantly this vaccine's efficacy against the severe disease was similarly high across regions [74,84].…”