Better 'immune training' in poorer countries led to fewer Covid-19 deaths: CSIR

The study looked at the co-relation between Covid-19 deaths and various factors such as urbanisation, sanitation, and population level prevalence of autoimmune diseases.

“Immune training” through repeated exposure to infections in poorer countries has led to fewer deaths due to coronavirus disease (Covid-19) in comparison to those that have a high GDP (Gross Domestic Product) and Human Development Index, says a study by researchers at the Council of Scientific and Industrial Research.

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The study, recently published in the journal Current Science, looked at the co-relation between Covid-19 deaths and various factors such as urbanisation, sanitation, and population level prevalence of autoimmune diseases.

“Better sanitation leads to poorer ‘immune training’ and thus could be leading to higher (deaths per million),” the study said.

“From the beginning of the pandemic, we have seen that a higher number of Covid-19 deaths were reported from high income countries. We wanted to look at the reasons. And, we found improved hygiene and better sanitation co-related with more deaths. So did a higher age profile of the population,” said Dr Shekhar Mande, director general of CSIR.

He said, “In Covid-19, once the virus enters the body it starts making copies of itself leading to the symptoms and the body fights it off by the tenth or twelfth day. However, around the eighth or ninth day, the body’s immune system goes into hyper-drive in some people and this is what kills them. So, we started looking at prevalence of other auto-immune conditions and these are the same countries that have a high prevalence of such diseases; there was a good co-relation.”

The researchers found a high co-relation of Covid-19 deaths with auto-immune conditions such as multiple sclerosis (a condition where the body’s immune system attacks the layer covering the nerve fibres), rheumatoid arthritis (where the immune system attacks the joint linings), type-1 diabetes (where the immune system destroys the insulin-making cells), and psoriasis (where the immune system attacks the skin cells and increases its production abnormally).

The study also looked at BCG vaccination coverage; several studies had hypothesised that countries with high anti-tuberculosis vaccine coverage saw fewer deaths because it trained the innate immune system of the body. However, the study found “negligible” correlation between the two.

“Although our study shows that countries with poorer hygiene practices and sanitation had fewer Covid-19 deaths, it does not advocate maintaining the poor hygiene conditions. The best way to reduce Covid-19 deaths is to protect against the infection by wearing masks. Other studies done by our lab have shown that Covid-19 is majorly airborne and wearing a mask can reduce the chances of getting the infection considerably,” said Dr Mande.

The study also added, “This analysis opens up avenues to consider ‘immune training’ with possibilities of microbiome therapies to supplement improved hygiene and sanitation practices.”