COVID-19: Can BCG vaccine fight this pandemic

Data showed countries that do not routinely immunise children against tuberculosis have more COVID-19 cases

By Vibha Varshney
Published: Thursday 02 April 2020
Epidemiological data showed the vaccine could be effective against the novel coronavirus (SARS-CoV-2) Photo: Pexels

Researchers across the world are testing the Bacillus Calmette-Guerin (BCG) vaccine against the novel coronavirus disease (COVID-19).

This vaccine is composed of a live, weakened strain of the bacterium Mycobacterium bovis, related to the tuberculosis (TB) pathogen Mycobacterium tuberculosis.

BCG — developed in the 1921 in France — is only 60 per cent efficient in controlling TB.

Epidemiological data, however, showed it could be effective against the novel coronavirus (SARS-CoV-2).

The data — yet to be peer reviewed — found that countries that do not routinely immunise children against TB have more COVID-19 cases.

These countries include the US, the Netherlands and Italy. Countries like Iran which started giving the vaccine late in 1984, had high mortality, suggesting that BCG protected the vaccinated elderly population.

There does not appear to be a direct evidence that a vaccine against a bacterial disease will work against viral infections.

It is likely, however, that BCG stimulates general immune response. This results in faster response to infections that could reduce severity of disease and lead to faster recovery.

It was shown recently that the vaccine defies our understanding of immunity.

Broadly, when a person is attacked by a microbe, the innate immune system kicks in.

Monocytes — types of white blood cells — penetrate the infected tissue, convert to macrophages and provide the first line of defence.

Vaccines, on the other hand, lead to the development of the acquired immune system in the human body. This works slowly and focuses specifically on certain invaders.

But Mihai Netea — a researcher at Radboud University in the Netherlands — shows that the innate immune system also has a memory. This is known as ‘trained immunity’.

Genetic material in an immune cell remains in a state of high alert for several months after an infection and this protects from new infections.

Netea found the BCG vaccination protected against infection with a weakened form of the yellow fever virus, according to a study published in January 2018 by journal Cell Host & Microbe.

This understanding can help lead to the use of the vaccine by health workers exposed to infected people every day.

“It is an interesting hypothesis, although it is important to emphasise that it is a hypothesis,” said Sam Behar, a professor at the Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, the US.

There are some unknowns in this idea, even though there is a basic understanding of what is happening, according to him.

It is now known, for instance, how long the training induced by BCG lasts. It is unlikely that it is more than a several months or a couple years.

In other words, people vaccinated as infants would not necessarily be protected as adults.

BCG re-vaccination is not always a benign phenomenon and the elderly often have poor responses to vaccines.

There is also little information whether innate immunity is effective against SARS-CoV-2.

The long incubation period suggests it is not detected by the innate immune system, said Behar.

The BCG vaccine seems to work in mysterious ways and is found to be effective in patients of inflammatory and autoimmune diseases as well.

Recent studies showed that it is effective in controlling blood sugar in people with diabetes type 1 and maintained better sugar levels for the next five years.

The likely mode of action is that the vaccine boosts a substance that helps disable immune cell attacks on healthy tissues, which occur in individuals with autoimmune diseases, such as type 1 diabetes.

It has also been found effective as bladder cancer therapy and increasing survival of low birth weight children.

Researchers are experimenting with a variety of existing drugs too, in an effort to fight the COVID-19 pandemic.

After the Middle East Respiratory Syndrome epidemic in 2012, they screened a variety of chemicals of their activity against the virus.

Chloroquine, developed in 1934 and used to treat malaria was one such chemical that showed good activity.

It is, however, not very clear why the drug works on a virus, similar to the BCG vaccine.

One theory is that chloroquines change the acidity at the surface of the cell, preventing the virus from infecting it.

The other theory is that chloroquine helps activate the immune response.

Researchers recently tested it in combination with an antibacterial drug (azithromycin) and found that this combination works better than chloroquine alone.

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