Could an anti-TB vaccine be protecting Nepalis?

Researchers have been puzzled about why while the COVID-19 pandemic ravages China, Europe and now North America, low-income countries in South Asia have so far recorded fewer cases. 

Public health experts say one reason is that the poorer countries just do not have enough kits to screen populations at risk for the virus. But others maintain that even there were a lot of infected people around, the coronavirus is not spreading in the subcontinent as aggressively as elsewhere.

There are many theories floating around to explain this, including the ‘hygiene hypothesis’ which seems to show that South Asians have developed a resistance to new viruses because the environment is not as sterile as in industrialised countries. Other scientists have speculated that countries with a high incidence of malaria seem to be relatively less affected, and have even proposed chloroquine as a cure.

One theory that appears more plausible is that people in countries that administer the anti-tuberculosis vaccine BCG (Bacillus Calmette-Guerin) seem to be less susceptible to COVID-19. Even before this pandemic, there had been epidemiological studies that indicated higher immune levels in people with BCG against communicable diseases, including viral infections.

Could Nepal’s surprisingly low caseload of novel coronavirus be attributed to the BCG vaccine which has been widely used in the population for the past five decades? The BCG vaccine campaign started in Nepal in 1979 under Expanded Program on Immunisation of the World Health Organization (WHO), and since then millions of Nepalis have been inoculated with it. 

The rates of morbidity and mortality from COVID-19 vary greatly in different parts of the world, and scientists have been trying to understand why. For example countries like Italy, the Netherlands and the United States that never had a comprehensive BCG vaccination program appear to be disproportionately imapcted. There are now tests going on in several laboratories in Europe to see if this is indeed true.

"If you superimpose a map of the world with coronavirus over countries that had a BCG vaccine program, there appears to be less virulent spread of COVID-19 in countries that inoculated children against tuberculosis. The number of cases may still be high, but the fatality rate is lower in BCG countries," explains Sameer Mani Dixit, a researcher at the Centre for Molecular Dynamics in Kathmandu. 

He adds that the BCG is not an anti-virus vaccine, but seems to build the body's immunity not just against tuberculosis, but also from viral infections. Recent research suggests that live attenuated vaccine like BCG stimulates the immune system and protects against wide range of diseases. It is also important to note that the vaccine is no means perfect, as it prevents about 60% of TB cases among children. In addition, the vaccine is less effective in preventing TB that affects the lungs and works better against severe forms of TB, such as tuberculosis meningitis. 

BCG vaccine’s effectiveness against COVID-19 is a hypothesis that is yet to be tested, researchers are starting clinical trials in Australia, the Netherlands and Germany that should answer the questions surrounding BCG in the near future. The trials are being conducted on people at high risk of exposure, primarily health care personnel. 

Buddha Basnyat, a physician at Patan Hospital believes that without randomised control trials the efficacy of BCG against COVID-19 is “just a conjecture”, and the tests need to prove beyond doubt that there is a correlation. 

“The link is unknown and it would require a lot of scientific studies to find the truth. Only, when the results of clinical trials are out can we be absolutely certain. In medicine, association is not enough, we need to show causal linkages, especially when there are so many confounding variable. Until then nothing is concrete,” adds Basnyat. 

Furthermore, it is also necessary to know for how long does the positive effects induced by BCG lasts in the immune system. Nepalis were vaccinated with BCG as infants, would that protect them as adults? Keeping a vigilant eye on the number of novel coronavirus cases in the BCG vaccinated countries is important. An exponential spread of COVID-19 cases in India could knock out the hypothesis completely, and there is also no explanation why China which has near universal BCG coverage was so badly hit. 

We could be clinging to straws, hoping that the BCG vaccine will save the day, but the authenticity of the hypothesis cannot be established till it is explored through rigorous clinical trials. Till then, public health experts warn, Nepal needs to maintain its lockdown, test and isolate groups around the country, especially western Nepal where tens of thousands of Nepali workers have come in from India in recent weeks. 

Read also: Countries cooperating to find COVID-19 cure, Buddha Basnyat

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