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Last Updated : Oct 30, 2020 04:27 PM IST | Source: Moneycontrol.com

Explainer: What the ICMR study tells us about the effectiveness of the BCG vaccine against Covid-19

Governments around the world are keen to know if the nearly century-old vaccine can be used to prevent Covid-19. It’s not hard to see why — the safety of the BCG vaccine has long been established. Moreover, it is very cheap and production can be scaled up easily

At a time when the world is looking for a Covid-19 vaccine, a study by the Indian Council of Medical Research (ICMR) has found that the nearly century-old Bacille Calmette-Guérin (BCG) vaccine may offer protection to elderly people. The BCG vaccine is given primarily to children to protect them from tuberculosis (TB).

Here is an explainer on what exactly the ICMR researchers have found, and why the BCG vaccine has come into prominence against Covid-19.

 Does the BCG vaccine prevent Covid-19?

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The ICMR researchers investigated the impact of BCG vaccination on major components of the immune system such as T cell, B cell, monocyte and dendritic cell subsets as well as total antibody levels in a group of healthy elderly individuals of age 60-80, one month after vaccination. The study, which was carried out to examine the effect of BCG on Covid-19, ran from July through September. It enrolled 86 individuals, of which 54 were vaccinated with BCG and 32 are controlled arm or non-vaccinated.

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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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The ICMR study found that the BCG vaccine boosts both innate and adaptive immunity, as well as total antibody levels in elderly individuals, suggesting its potential utility against the SARS-Cov2 infection by enhancing heterologous immunity. In this, the immune response against one pathogen can also provide immunity to another, unrelated one. The innate immunity is the immediate response of the immune system to a virus infection; adaptive immunity develops over days and weeks.

The study has been published as a preprint (non-peer reviewed) in medRxiv.

 Does the study have any limitations?

The study suggests the potential utility of a BCG vaccine against SARS-Cov2 by enhancing heterologous immunity. But it does not state whether the immune response generated by the BCG vaccine provides protection against Covid-19. A large clinical trial alone will be able to answer this question.

How did the BCG vaccine come into prominence?

The BCG vaccine came into prominence during the early stages of Covid-19, with at least three preprints that compared the incidence of Covid-19 cases in countries where the BCG vaccine is used against countries where it is not used, and observing that countries that routinely used the vaccine in infants had fewer reported cases of Covid-19.

Epidemiologists have warned that such studies are prone to significant bias from many confounders, including differences in national demographics, disease burden, testing rates for Covid-19 virus infections, and the stage of the pandemic in each country. It was later shown that countries that had universal BCG vaccination, such as India and Brazil, had seen a significant jump in Covid-19 infections.

But this didn't stop researchers from India, The Netherlands, Australia and Germany conducting clinical trials to study the efficacy of the BCG vaccine against Covid-19.

In India, the Serum Institute of India is conducting a phase III clinical trial of a BCG vaccine candidate, VPM1002, to evaluate its ability in reducing Covid-19 infections and severe disease outcomes among high-risk people of advanced age, those with comorbidities and high-exposure healthcare workers (HCWs),

Does the BCG vaccine hold any potential advantages?

If the BCG vaccine has any proven positive prophylactic effects on Covid-19, it may have a tremendous benefit both clinically and economically. The safety of the BCG vaccine has been long established. Moreover, it is very cheap and production can be scaled up easily and is therefore an attractive option for the governments.

What is the WHO's stance on BCG for Covid-19?

The WHO does not recommend BCG vaccination for Covid-19 due to the absence of evidence that it works. The world health body continues to recommend neonatal BCG vaccination in countries or settings with a high incidence of tuberculosis. Two clinical trials addressing this question are underway, and the WHO said it will evaluate the evidence when it is available.
First Published on Oct 30, 2020 04:27 pm
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