ALTHOUGH Covid-19 cases have been increasing in Pakistan, the rate of spread and number of deaths have not been as dramatic as in many other countries. The case fatality rate in Pakistan so far is 2.1 per cent, while it is 5.6pc in the US, 6.3pc in Iran, and 13pc in the UK and Italy. One reason could be that a large proportion of people tested initially were returning travellers and participants of the Tableeghi Jamaat ijtema. This is a relatively younger and fitter population which is more likely to have better outcomes. As we test more of the symptomatic people in the general population, the fatality rate may increase. It is possible that we may still end up with similar or even worse outcomes than some of the countries in Europe and North America.

It is important to understand the reasons behind what appears to be relatively better outcomes in Pakistan so far. The timely lockdown measures may have helped. The relatively younger population in Pakistan may explain some of the differences. Only 7.6pc of our population is over 55 years, while this proportion is 19pc in the US. However, this is unlikely to be the only explanation.

Genetically, there are negligible differences in the virus circulating in Pakistan as compared to the rest of the world, so viral factors seem unlikely. There are three additional hypotheses that could explain the milder disease impact in our part of the world so far.

Firstly, there may be environmental factors that could have decreased the virulence or transmissibility of the virus in our part of the world. Temperature, humidity and UV light exposure are known to affect the seasonality of different respiratory viruses across the world. Despite decades of research, we still do not know for sure why particular respiratory viruses like influenza, RSV, etc attack a particular area every year at the same time. If this theory of environmental influence is correct, then Pakistanis travelling to another country should be no more protected and would be at similar risk as the native population. Other than undertaking a challenging epidemiologic study on this, it would be quite difficult to quickly prove or disapprove this hypothesis.

What can explain our relative safety so far?

A second hypothesis to explain the lower death rate (if it is true) in Pakistan would be that our population has better general immunity than people in the First World. The BCG and polio vaccines have been hypothesised as a possible boost to our immune system against the coronavirus through some unknown mechanism. Besides poor diet, a major factor responsible for the lower height of our population compared to Western populations is that we are exposed to a large number of germs and our body spends a larger proportion of its energy reserves in constantly driving its immune system to work in high gear.

While this diversion of energy to the immune system compromises our growth, it may be an advantage when it comes to fighting novel infections. Our adaptive immune system may be as naïve against this new virus as any other population, but our innate or generic immune system might be more active and doing a better job in fighting this virus compared to people in the West. If this theory is correct, then people moving out of Pakistan would continue to be protected against Covid-19 at least in the short term.

Besides carrying out a complex epidemiological study, this hypothesis could be tested by taking blood from Pakistani and Western subjects and comparing the samples to see how well they neutralise the virus or what kind of immune response they generate when exposed to the novel coronavirus. So far, experiments to prove this hypothesis have not shown a positive result but more research is needed.

A third hypothesis could be that people anywhere in the world who suffer from Covid-19 complications have some immunologic vulnerability that others, who recover quickly, do not have. If this theory is correct, then this immunologic vulnerability would be shared by people who experience a severe form of the disease anywhere in the world. One can hypothesise that the proportion of people with this vulnerability is higher in certain other countries compared to our part of the world. To test this, blood samples from those with severe Covid-19 in Pakistan and other countries could be compared with the blood of those who contracted the infection but quickly recovered. Such studies are being done but there is nothing conclusive as yet.

While Pakistan is not out of the woods and, in fact, the worst may be yet to come, it is important to study the factors which could explain our relative safety so far. There may be lessons which could help Pakistan and the rest of the world.

The writer is professor of paediatric infectious diseases and associate dean of research at the Aga Khan University.

Published in Dawn, April 30th, 2020