Interaction between malarial transmission and BCG vaccination with COVID-19 incidence in the world map: A changing landscape human immune system?

BackgroundCOVID-19 (Corona virus Disease-2019) is a new public health emergency and is a pandemic currently. Incidence and mortality of COVID-19 vary in different geographical areas. In this study we aimed to analyse the relationship between malaria transmission and BCG vaccination with COVID-19 incidence in the world map. Materials and methodsWe collected malaria cases data (World Health Organisation (WHO), 2018), worldwide COVID-19 cases and mortality data (European Centre for Disease Prevention and Control) and data on BCG vaccination. COVID-19 incidence and mortality was compared. FindingsData on 5316978938 persons from 166 countries were analysed. Malaria incidence rate was negatively correlated with COVID-19 incidence rate (correlation coefficient = -0.513, p<0.001). Malaria free countries had significantly higher number of COVID-19 cases compared to malaria endemic countries. In Europe and Americas, countries, which have higher BCG vaccination coverage, had significantly less mortality per thousand population compared to those with low BCG coverage (median 0.0002 (0-0.0005) vs 0.0029 (0.0002-0.0177), p=0.017). The case fatality ratio of COVID-19 was related nonlinearly to the malaria incidence. ConclusionsThe results suggest the changing human immune system as we progress to eliminate parasitic diseases with time. Chloroquine exposure in malaria endemic zones might have a protective effect. Summary boxO_ST_ABS"What is already known on this subject?"C_ST_ABSTo the best of the authors no similar evidence, of the effect of malarial transmission on the COVID-19 global distribution is known. The effect of the Bacille Calmette Guerin (BCG) vaccine on modifying the human immune system has been reported before and is postulated to protective against certain viral infections like Influenza A (H1N1) and herpes virus. "What this study adds?"This study finds that COVID-19 incidence, worldwide is less in countries, which are malaria-endemic. In the European and American countries, increased BCG coverage may have some mortality advantage against COVID-19. The case fatality rate was related to malaria incidence, however, in a complex way. This could be a window into the changing landscape of human immune system as we progress to eliminate parasitic disease with time or this could be due to long-term protective body level of anti-malarials like chloroquine or hydroxychloroquine in countries with higher malaria incidence rate.