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India Study Finds Covishield Is 63.1% Effective Against SARS-CoV-2 Infection

India Study Finds Covishield Is 63.1% Effective Against SARS-CoV-2 Infection

A nurse displays a vial of Covishield at a medical centre in Mumbai, January 16, 2021. Photo: Reuters/Francis Mascarenhas

  • A new study by scientists in India has reported that Covishield is 63% effective at preventing a SARS-CoV-2 infection.
  • Noted virologist Shahid Jameel said the study was “carefully done” and that its results were “very reassuring”.
  • The study also reported that Covishield could prevent moderate-to-severe disease in 81.5% of cases.

New Delhi: A two-dose course of the Covishield vaccine has been found to be 63.1% effective against SARS-CoV-2 infection, in a real-world study conducted by scientists in India. Their findings were published in an online paper by The Lancet Infectious Diseases journal on November 25.

(The paper doesn’t say if the effectiveness is against symptomatic or asymptomatic infections.)

The ‘participants’ of the study were people who visited two Faridabad-based medical institutions between April 1 and May 31, 2021: the Employee State Insurance Corporation Medical College Hospital (ESICMCH) and the Translational Health Science and Technology Institute (THSTI).

The researchers, according to the paper, numbered 33 in all and were affiliated with ESICMCH, THSTI, the Institute of Genomics and Integrative Biology, the Regional Centre for Biotechnology (Faridabad), the National Institute of Immunology and the International AIDS Vaccine Initiative.

The delta variant was the dominant strain of the virus in the country at the time of the study, and was in fact driving a major surge.

The results are comparable to an effectiveness study that scientists in the UK had conducted among recipients of the same vaccine, and had published their results in July 2021. In this case, the vaccine was found to be 67% effective against symptomatic infections of the delta variant.

Shahid Jameel, noted virologist and a visiting professor at Ashoka University, Haryana, called the Indian study’s results “very reassuring”. “Glad to see this carefully done study on a vaccine that is the mainstay of India’s vaccination programme,” Jameel told The Wire Science.

The study also reported that Covishield could prevent moderate-to-severe disease in 81.5% of cases.

Incidentally, a study published by the same journal earlier this week reported that Covaxin, the other major Indian vaccine against COVID-19, had a real-world effectiveness of 50%. But this study was held back by its failure to assess Covaxin’s ability to prevent moderate and severe forms of the disease.

Both studies had the same design, called ‘test-negative case-control’. Such studies are observational in nature: scientists sort the participants into two groups – those who got the disease (‘cases’) and those who didn’t (‘controls’) after a full course of vaccination – and compare them on various parameters. ‘Test negative’ means recruits who test positive for a disease are grouped under ‘cases’ and those who test negative, under ‘controls’.

The effectiveness studies for both Covaxin and Covishield were also conducted around the same time – April-May 2021. However, the Covaxin study, conducted by doctors at the All India Institute of Medical Sciences, New Delhi, was limited to healthcare workers. Healthcare workers are more exposed to the virus and thus have a higher risk of infection.

The Covishield study, on the other hand, was not limited to high-risk groups: it involved all those people who visited the two hospitals in Faridabad to get tested for COVID-19.

Protection against variants

The Covishield study found that the vaccine protected more against the ‘original’ strain of the novel coronavirus compared to the other variants, at least in terms of the level of neutralising antibodies it induced in the body. (These antibodies prevent the entry of viruses into cells.)

The mean titre, or volume, of neutralising antibodies against the original strain was 599.4 – but only 88.4 against the delta variant. Against the alpha, beta, and kappa variants, the titres were, 599.4, 112.8, and 97.6, respectively.

More significantly, the study found no noticeable difference between the protection against infections of the delta variant and that against the original variant afforded by vaccine-induced cellular immunity. Cellular immunity is the body’s response to a virus after it has evaded the antibodies and entered a cell. This response is longer term and is responsible for actually killing the virus.

“We found no significant differences with regard to T-cell immune responses against wild-type or the delta variant of SARS-CoV-2,” the paper reads. “These observations are consistent with a previously published report.”

As with severe disease, the Covaxin effectiveness study didn’t say anything about cellular immunity either.

Ramachandran Thiruvengadam, the lead author of the Covishield study, had penned an independent commentary accompanying the paper of the Covaxin study.

He and his co-authors wrote: “Future studies should be designed with an emphasis to evaluate protection against moderate-to-severe COVID-19 and to analyse immune correlates of protection, such as neutralising antibodies and antigen-specific T-cell response, against the wild type and the delta variant.”

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