Are COVID-19 rates inversely related to the death rates by Influenza and Pneumonia?

India has imposed a harsh coronavirus related lock down. This lock down has been imposed even though seemingly there is no evidence yet, nor officially conceded, of community transmission. Nor has the possibility that the Indian situation, as a tropical country with already a high burden of flu and pneumonia related deaths, may have some immunity to the SARS-CoV-2 virus, been considered.

We shall first investigate our hunch that COVID-19 rates are inversely related to the death rates by Influenza and Pneumonia and that it is different from what is normally expected. If this is true, then there is the factor ‘cross immunity’ or ‘cross protection’.to be considered, that prior infection with one virus affords protection against closely related ones.

From the portal

https://www.worldlifeexpectancy.com/cause-of-death/influenza-pneumonia/by-country/

we can obtain influenza and pneumonia related death rates per 100,000 of population. We also have the actual or estimated count of deaths from Covid-2 as of 28/03/2020 for many countries. Influenza and pneumonia are a natural cause of death in old age in tropics, irrespective of the quality of health care and it is reasonable to expect that the same is true with the new SARS-CoV-2.

Table 1 shows the deaths from Covid-19 as of 28/03/2020 from https://www.worldometers.info/coronavirus/ and Flu-Pneumonia deaths per year per 100000 of population from https://www.worldlifeexpectancy.com/cause-of-death/influenza-pneumonia/by-country/. Figure 1 shows the scatter plot of the flu or pneumonia deaths per hundred thousand of population against the SARS-CoV-2 deaths 28/03/2020 for some representative countries or regions. The data point for China, represents that for Hubei province, as this province was isolated in a lock down. Generally, it is seen that countries with higher flu/pneumonia death rates have much lower deaths due to SARS-CoV-2. Countries like Philippines, Singapore, Malaysia which have been exposed for durations longer than Italy and Spain show much lower mortality rates due to Covid-19. Angola, Algeria (DZA), Ethiopia and Kenya have been included in this list because they have the largest number of Chinese foreign aid project workers and could have been exposed early.

There seems to be evidence of enhanced immunity to the new corona virus in tropics, because of the greater exposure historically to influenza viruses in the region. In tropical regions, with circulation of influenza virus throughout the year, we expect the population to have heightened inflammation and antibodies with at least some affinity to a new corona virus. Antibodies with specific affinity to SARS-CoV-2 are generated by a process of selection of increasing affinity when challenged by a viral antigen. Weak affinity gives a head start to the immune response. In epidemiological language, this translates to lower infectivity and lower mortality.

What Singapore and Malaysia influenza data show (the rates being higher than that for India which has far inferior health care facilities) is that influenza as cause of death is almost independent of quality of health care – availability and access to critical care. This is because, there is a continuous challenge between virus and antibodies, with virus kept under check by the immune system at younger age and succumbing with age. To study this, we need age wise data to separate the effects and this has not been attempted here. India was exposed late and is still at the very early stages but has imposed a very harsh lock down. With time, as the SARS-CoV-2 infection spreads, the numbers for India will peak. So far, the highest numbers are seen for ITL. Iran is already close to peak and CHN (Hubei) is past the peak. As disease spreads, we expect other countries to reach the line passing through CHN, ITL and IRN on the log-log plot. India should therefore have a rate similar to that of Brazil, which by simple interpolation will indicate about 5200 deaths in India due to the SARS-CoV-2 virus when infection has reached the stage at which Italy and Iran are on 28/3/2020.

To put a better perspective on our arguments above about cross immunity, we shall compare death rates by Influenza and Pneumonia to that from tuberculosis (TB) and that it is what is intuitively expected. If this is true, then there is the factor of ‘cross immunity’ or ‘cross protection’.to be considered when we handle the Covid-19 threat, that prior infection with one virus affords protection against closely related ones. Table 2 compares the Flu- Pneumonia deaths per year per 100000 of population with those from tuberculosis from https://www.worldlifeexpectancy.com/cause-of-death/influenza-pneumonia/by-country/. Figure 2 shows the scatter plot of the flu or pneumonia deaths per hundred thousand of population against the death rates from tuberculosis for a representative set of countries. We see a positive trend and correlation – there is seemingly no cross immunity factor here. We have also marked what we call the trend lines and the skylines and shorelines of the scale dependent stratification in the scatter plot. The TB rate is lower with better public health facilities expected of the countries with much higher per capita income. Whereas, for flu there is only weak dependence on health infrastructure. It is your body that protects against flu, not doctors or ventilators. When faced with a new virus, again the body must defend itself.

Concluding remarks

Using data available in the public domain:

https://www.worldlifeexpectancy.com/cause-of-death/influenza-pneumonia/by-country/

we showed that so far COVID-19 death rates are inversely related to the death rates by Influenza and Pneumonia. This suggest that there is the factor of ‘cross immunity’ or ‘cross protection’ to be considered, that prior infection with one virus affords protection against closely related ones. To put a better perspective on our arguments about cross immunity, we compared death rates by Influenza and Pneumonia to that from tuberculosis (TB) and obtained a positive trend and correlation as intuitively expected. The main takeaway from our study can be summarized thus: It is your body that protects against flu, not doctors or ventilators. So, when faced with a new virus, it is the body that must defend itself. Younger and healthier persons are therefore much more resilient than older and weaker ones.

Table 1. Deaths from Covid-19 as of 28/03/2020 are from https://www.worldometers.info/coronavirus/ and Flu-Pneumonia deaths per year per 100000 of population from https://www.worldlifeexpectancy.com/cause-of-death/influenza-pneumonia/by-country/

Figure 1. Scatter plot of Covid-19 deaths per 100000 of population vs the number of deaths per year per 100000 caused by Flu-Pneumonia

Table 2 compares the Flu-Pneumonia deaths per year per 100000 of population with those from tuberculosis from https://www.worldlifeexpectancy.com/cause-of-death/influenza-

Figure 2. The scatter plot of the flu or pneumonia deaths per hundred thousand of population against the death rates from tuberculosis for a representative set of countries.

Ajit Haridas and Gangan Prathap