Covishield only 33-60% effective against Delta variant of SARS-CoV-2, warns top US health expert

American epidemiologist Eric Feigl-Ding, who is a senior fellow at the Federation of American Scientists, has warned that the Oxford-AstraZeneca COVID-19 vaccine is only 60 percent effective against the Delta variant.

The Delta variant, which has been dubbed a variant of concern by the World Health Organization (WHO), was first detected in India and is believed to have catalysed the explosive second wave of the pandemic in the country.

The triple mutant variant referred to as the B.1.617.2 strain by scientists and doctors has the potential to elude the AstraZeneca vaccine (Covishield). Eric Feigl-Ding has warned that one shot of the Oxford jab has limited effectiveness (at around 30 percent) against the Delta strain of SARS-CoV-2. This news is of particular concern to India as Covishield is the most extensively administered vaccine in the country.

Citing a study, Eric Feigl-Ding tweeted: “The efficacy of AZ [AstraZeneca vaccine] against Delta variant is not 90 percent (it is 60 percent), Pfizer is 88 percent in one non-trial study. However, one dose of the vaccine (both types averaged) is just 33 percent. And many countries are just one dose vaccinated.”

NEW—UK reports that 2 doses of AstraZeneca vaccine efficacy for #B16172 India variant: just 60%. And latest study says #B117 efficacy just 66% (lower than before). 1-dose efficacy 33% for #B16172.

Clearly #B16172 problematic in when 2/3 of shots is AZ https://t.co/qyly22qmDBpic.twitter.com/tf2V1HCeCg

COVID-19 Vaccine

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How does a vaccine work?

A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.

How many types of vaccines are there?

There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.

What does it take to develop a vaccine of this kind?

Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.

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— Eric Feigl-Ding (@DrEricDing) May 23, 2021

The noted American health expert cautioned: “Please take Delta variant seriously — it’s the fastest transmission variant known to date. Much, much faster. And it has somewhat vaccine evasion, especially 1 dose, and it is much more severe (higher risk of hospitalisation).”