--BY Rukhsana Shaheen
Although epidemiological analysis shed light on the spatial and temporal dynamics of pandemics of communicable disease, but probably, such approaches fall short to consider the geographical context related to social factors in which transmission occurs. This is true for COVID-19 pandemic too. The presence of pathogen SARS-Cov-2, a novel coronavirus, in a place is a necessary condition for COVID-19 transmission, but it is not the only condition for pre-pathogenesis or pathogenesis of the disease. Generally, vulnerability to a communicable disease is strongly associated with poverty, but in case of COVID-19, poverty is not a major issue, it affects one-to-all irrespective of wealth status. Related with geographical variations in different continents and regions of the world, there are wide inequalities in people’s exposure to pathogen, their abilities to cope wit hand resist disease, and their access to effective treatments. People’s vulnerability to infectious diseases stems from three processes: their levels of exposure to pathogens, their resistance to pathogenic effects after exposure, and their ability to recover from infection.
Human exposure to SARS-Cov-2 is largely a product of the social and built-in total environment in which people live, and their behaviors and social interactions in different geographical area. While human mobility clearly plays a key role in COVID-19 pandemic, ironically, immobility is also critically important in sustaining the pandemic. Human immobility means that they are not often long-distance carriers of COVID-19, but confinement to isolated spaces means that they do not have the means to escape infection. These spaces serve as ‘epidemic pumps’, sustaining infections during non-epidemic periods and providing a base for transmission to new populations. Pandemic of COVID-19 emerge and spread through a diversified complex mix of social, biological, and environmental factors. Their heightened potential for spread is closely linked to the rapidly expanding global flow of people and products in increasingly globalized world.
In general, it is said that in any communicable disease if 80% of the population can develop immunity either naturally through clinical or subclinical infection, or by immunization, then the rest of the 20% population will not need any intervention and will be protected. If this is considered for COVID-19, then 80% population of a country have to acquire natural immunity as there is no vaccine, but in the process there will be immense loss of life, this is not ethical either. Moreover, as the SARS-Cov-2 is frequently mutating and changing strain, immunity too will not be constant. Viral change/mutation probably varies with environmental factors, which will probably lead to durable or sustained pandemic for some time more, may be till a core vaccine is found. It is seen that some countries have been able to limit the spread of COVID-19 not through increasing immunity, but appears to be through strict implementation of protective/preventive measures at individual level for each and everyone. These measures stress on covering up the route of entry and exit of the virus, that is, the respiratory tract, by appropriate use and management of face mask.
Many experts, based on mathematical modeling and experience of other countries, are projecting the trend and longevity of COVID-19 in Bangladesh. But this appears to be more of rhetoric, as COVID-19 pandemic depends on many factors –virulence and pathogenicity of virus (considering mutation); physical, geographical, biological environmental factors; host (person) factors; viral load/dose response; biological plausibility and temporal relation; containment efforts by health workers; and compliance with the containment efforts by the public. There is no individual linear relationship among these factors, rather a complex that may lead to either increase over longer period or rapid decrease. Time bound predictions may be avoided.
[The writer is a retired Assistant Professor of Community Medicine]
Predication of Sustainability of Covid-19 Pandemic
--BY Rukhsana Shaheen