Socio-Demographic Factors Influencing Case Fatality Rate of Covid-19: A Review Article

The covid-19 pandemic has serious outcomes on world in terms
of economic destabilization, mortalities, worsening of morbidities...


Introduction
The covid-19 pandemic has serious outcomes on world in terms of economic destabilization, mortalities, worsening of morbidities and a state of unreality. The SARS-COV-2 emerged as a viral illness in Wuhan province of china and in a short time becomes pandemic because of its high infectivity, virulence and having ability to spread in incubation period. This virus belongs to coronavirus family and it cause mainly respiratory tract illness. Covid-19 cause severity of symptoms in patients with comorbidities and elderly. Other than respiratory symptoms, it causes multi-inflammatory syndrome in children and presentation of this syndrome is unusual and has some features in similarities with Kawasaki disease [2].
There are various drug trials for treatment of covid-19; however, no drug regimen is approved by FDA till now.
This review article will explain the few factors that why there is difference in reported case numbers and case fatality rate in developing and developed countries. The symptoms, duration of symptoms and response to treatment vary in individuals; thus, it is different in countries and may be due to genetic variation along with difference of ethnicity. It is a debatable topic, and the results of research will help to understand the disease process and to combat infectious diseases. The subsequent text will explain few factors which are currently not available in collaborative way.

Methods and Materials
This is a systematic review article. A literature search was done by using PubMed and google search engine for original and review articles, advisories from professional societies and expert publications since the onset of current covid-19 pandemic.

Discussion
Coronavirus are spherical or pleomorphic enveloped RNA viruses. They are transmitted via airborne droplets to nasal mucosa.

Mode of Transmission and Detection of Virus
SARS was first transmitted from civets to humans in china and then human-human by respiratory secretions (e.g. families, hospitals). It was mainly transmitted by respiratory droplets and invade via respiratory membrane. SARS-COV-2 was transmitted via bat to humans and then human-human by respiratory secretions and close contact makes its spread more progressively [4,5].
Detection of virus is done by using antigen/antibody by ELISA, Nasopharyngeal/oropharyngeal swab by PCR to detect nucleic acid

Symptoms
The period between the introduction of virus into the body and the onset of symptoms is called incubation period and it usually lasts for 4-14 days in coronavirus infection. Symptoms varies from person-person in severity and duration; however, the percentage of symptoms [5,6] are as following;

4.
Loss of sense of smell and touch 30-40%

Shortness of breath 20%
The percentage of unusual symptoms are not available till

date. It causes inflammatory syndrome in children and systemic
vasculitis. It is also reported that it affects clotting pathway and cause death due to pulmonary embolism [1,7]. There are differences between symptoms of covid-19, common cold and other allergies (common cold is usually self-limiting and does not cause severe myalgias ( Figure 3).

A. Population Age Structure
Population age structure of different countries varies and it is estimated that countries having high growth rate and young median age has low mortality rate by ovid-19 pandemic; although, it opens a new debate and will surely lead to new aspect of population studies and control strategies [9] ( Table 2).  (Figure 4). The mortality rate of covig-19 is surprisingly low in developing countries in contrast to predicted outcome as the countries having high growth rate and young median age shows low mortality rate as shown in below Figure 5 [10].

B. BCG Vaccination and Covid-19
Bacillus-Calmette-Guerin is almost a 100-year-old vaccine against a dreadful bacterium known as Mycobacterium Tuberculosis which cause a disease Tuberculosis affecting different organs.
Research indicates that it is 70-80% effective in protecting against few forms of tuberculosis (for example pulmonary tuberculosis, tuberculosis meningitis). It is recommended as a part of Expanded program of Immunization and administered to newborns immediately after birth. The countries which are prioritized for BCG vaccination due to high tuberculosis load has showed less fatality rate due to covid-19 [5]. Tuberculosis affects different organs with different severity; however, it initially affects lungs and spread via respiratory droplets.

BCG protects us from Tuberculosis and other respiratory
infection (influenza, pneumonia) [11]. There is currently no evidence that BCG helps in protection against covid-19; however, studies in Germany and Netherland support this evidence. In the midst of pandemic, it is early to jump on conclusion and surly it may help to build a vaccine against covid-19 and opens a new chapter in history [12]. Tuberculin Skin Test is an example of Type 4 hypersensitivity reaction; thus, it supports that BCG increase one's response to Type 4 hypersensitivity reaction (Potentiate the host response via T-Lymphocytes), immune system part which fight against covis-19.

Summary
This review article emphasizes the socio-demographic factors for difference of mortality rate due to covid-19 in developing countries. This difference of case fatality rate is surprising, and it urged many researchers worldwide to re-explore the facts. There is difference in population age structure, immunization practices and use of Malarial prophylaxis along with cultural, regional and societal differences. Medicine is a continuous education and it evolves with time. There is no specific theory, thus it demands research and analysis of various factors which in result help us to fight against infectious diseases. There is limited availability of data at time; however, it opens new chapters of research in public health too and thus help to save more lives.