Covishield Vaccine 63.1% Effective Against Delta Variant Of Covid-19: Indian Study In Lancet

The study to evaluate the real-world effectiveness of Covishield vaccine against the Delta variant was led by Indian researchers from Translational Health Science and Technology Institute.

New Delhi: A real-world study conducted by Indian researchers has found that a two-dose course of the Covishield vaccine is 63.1% effective against SARS-CoV-2 infection attributed predominantly to the Delta variant. The findings were recently published by The Lancet Infectious Diseases journal. 

The Covishield vaccine (ChAdOx1 nCoV-19) is largely driving the vaccination programme in India.

SARS-CoV-2 has affected more than 262 million people worldwide, claiming over 5.2 million lives as of November 30. The Delta variant or B.1.617.2 is the dominant strain of the virus in India and most nations. 

The study to evaluate the real-world effectiveness of the Covishield vaccine against the Delta variant was led by Indian researchers from the Translational Health Science and Technology Institute (THSTI).  

Evaluating The Real-world Effectiveness Of Covishield

Between April 1 and May 31, 2021, the researchers compared as many as 2,379 cases of RT-PCR confirmed SARS-CoV-2 infection with 1,981 controls, at two medical research centres in Faridabad, India, the study said. During this period, there was a surge in Covid-19 infection in India. 

The vaccine effectiveness in completely vaccinated individuals against moderate-to-severe disease was found to be 81 per cent, the study said.

The effectiveness of single-dose vaccine against infection was found to be 46.2 per cent, according to the study.

The researchers observed that the spike-specific T-cell responses provide protection against both the Delta variant and wild-type SARS-CoV-2. 

The waning humoral immunity against the SARS-CoV-2 variants can be compensated for by the cellular immune protection provided by the vaccine, the study noted. 

High Levels Of Protection Against Moderate-To-Severe Covid-19

The findings suggest that two doses of the Covishield vaccine provide protection against infection with the SARS-CoV-2 Delta variant, and high levels of protection against moderate-to-severe Covid-19, the study said. The vaccine-elicited antibodies primarily prevent virus entry into host cells. However, the reduced neutralisation effect of these antibodies increases the possibility of infection with a variant of concern, the report said. 

The authors noted in the study that T-cell mediated immune responses conferred by the vaccine can provide protection against severe disease.  

In order to overcome the threat posed by the Delta variant and other emerging SARS-CoV-2 variants, the Covid-19 vaccination policy should encourage two doses of the Covishield vaccine in addition to other epidemiological public health measures, the authors noted in the study.