The coronavirus disease (Covid-19) first appeared in the Wuhan district of Hubei province of China in early December 2019. The first case was reported by China on January 7, 2020, and this aroused variable interest worldwide, with most countries initially ignoring the novel infection. Fortunately, Indian health authorities sensed the danger, largely because the country has always been alert to new infections. The scientific think-tank at the Indian council of Medical Research (ICMR) became active immediately and the first laboratory confirmed case was identified at ICMR's National Institute of Virology (NIV), Pune, sometime towards the end of January.
A look at the world Covid meter shows that there is striking variation in mortality rates across countries, ranging from 0.2% to 15% depending on age, the smoking habit and pre-existing co-morbidities. It may be too early to tell, but in general, countries in the Northern hemisphere have faced the maximum brunt, and those in the Southern hemisphere (and those located proximate to the Equator) have so far escaped high infection numbers.
Three factors seem to be playing a role in the observed lower numbers in India with almost zero occurrence of severe Covid-19 cases (until now). First, broad-based immunity in the population due to the extensive microbial load. The Indian population has been exposed to a vast variety of pathogens, including bacteria, parasites and viruses leading to the generation of broad specific memory T-cells in the system, ready to attack additional foreign invaders.
For example, the three main killers of Tuberculosis, HIV and Malaria have plagued India, Africa and several countries in the Southern hemisphere much more than the European and North American nations. In the context of CoV-2 coronavirus, the beneficial role of chloroquine and hydroxychloroquine has been much talked about and debated, while there has already been an extensive usage of this drug at the community level in India -- this too may ultimately prove beneficial.
Second, epigenetic factors that include environment and food habits may also play a beneficial role for countries such as India; much literature is already available in Ayurveda and other Indian systems of medicine on the definitive beneficial effects of Indian spices in augmenting immunity.
Third, and most important, is the possible role of immune response genes in the Indian population. These genes are collectively referred to as comprising the human leucocyte antigen system or simply, the HLA genes. Their main biological function is to present invading foreign antigens to the immune systems, since T-cells, which act as the body's soldiers come into play only when pathogens are presented to them in a more formal manner in association with HLA genes. In other words, the pathogen must first attach to compounds created by HLA genes before T-Cells attack it. If no such compounds are produced by the body, then the T-Cells are ineffective. As a consequence of the microbial load, the Indian population possesses a high genetic diversity of HLA, much more extensive than Caucasian populations. Indeed, studies by the author at the All India Institute of Medical Sciences, New Delhi, over several decades revealed the presence of several novel HLA genes and their alleles in the Indian population, most of which do not occur in other ethnic groups. Such genetic diversity of HLA could affect viral fitness.
The question then is: Why should genetic variation in HLA genes play a role in the Covid-19 progression? One hint comes from earlier studies in related viral diseases: Certain genetic variants of the HLA system provide protection against such viruses, while others increase genetic susceptibility to them. Another source of indirect evidence comes from recent clinical Covid-19 studies which showed that rapid T-cell response appears to be crucial for recovery from Covid-19, and reduced functional diversity of T cells in peripheral blood could predict progression of Covid-19.
The big question is: Does this give Indians a better chance at fighting the virus effectively? From the epidemiological data so far, it seems so (although much more extensive research is required). However, it is important for us to keep viral loads in check and below the threshold levels. In this context, the complete lockdown announced by the government is highly timely and most desirable. It is imperative that the virus replication cycle gets disrupted as early as possible before it gains numbers that may become difficult for us to counter.
To this end, the images of crowds gathering in several places whether for panic buying or interstate movements are disturbing. They could jeopardise all efforts and mitigate whatever natural advantages we enjoy.
The State must act fast to enforce the lockdown, even forcibly if necessary. India may be the outlier in fighting the coronavirus infection and succeed in keeping the overall numbers lower than the rest of the world with minimal deaths.
Narinder Kumar Mehra is the ICMR National chair and former Dean of the All India Institute of Medical Sciences, New Delhi