A study demonstrates the effectiveness of the Covishield vaccine

A community cohort study demonstrated the efficacy of two doses of Covishield against the delta variant in the general population of Chennai. Vaccine efficacy against SARS-CoV-2 in the 45+ age group was nearly 61% at least two weeks after receiving the second dose of Covishield.

The study, a collaborative effort between the National Institute of Epidemiology-Indian Council of Medical Research and Greater Chennai Corporation, was conducted from May 22 to September 30, 2021 during the waning phase of the second wave of COVID-19 in the town.

Of the 20,913 households in the three divisions of Chennai, 19,211 were enrolled in the cohort. There were a total of 69,435 people residing in these registered households. A fifth of the households were in slums and 95.5% were pucca houses. Of the 69,435 people, 21,793 people were aged 45 and over, according to the study published in ‘Vaccines’.

Over the three-month period, the researchers followed these 21,793 people. While 7,735 people were unvaccinated, 10,762 people received the Covishield vaccine – 4,052 people received a single dose and 6,710 had taken two doses. A total of 59 people were excluded from the 6,710 people who had taken two doses for reasons such as past infections. As many as 3,296 people vaccinated with Covaxin and other vaccines were excluded.

Sharan Murali, one of the lead authors, said he designed a community cohort to study the real effectiveness of the vaccine. “We followed them for three months and checked if they developed the disease,” he said.

In the cohort of 45 years and more than 21,793 people, 303 tested positive for COVID-19 during the study period. Of the 14,305 people (6,651 received two doses and 7,654 unvaccinated) who were included in the primary analysis of vaccine effectiveness, 143 tested positive for COVID-19. Of the 143 people, 36 had received two doses and 107 were unvaccinated. The study found an overall vaccine effectiveness of 61.4% in the 45+ category.

“Through this, we recommend that the two-dose vaccination be ensured. Those who are still unvaccinated should start taking the vaccines as they will protect one way or another,” he said.

Sara H. Byrd