Epidemiology of COVID-19: What changed in one year?

A coronavirus brought the first pandemic attack of this century as a flu virus did a hundred years ago. This greatest pandemic of the century brings us new opportunities to understand and explore the dynamics of a contagious disease. Nearly two years later, we are still collecting the evidence to understand the disease. Some basic epidemiological properties are still urgently needed. Not only the origin of the virus but also Ro value, possible transmission routes, epidemiologic curves, case fatality rates, seasonality, severity and mortality risk factor, effects on the risk groups, differences between countries and so on still require strong evidence prior to making final suggestions. In this review, we tried to evaluate the epidemiological evidence to scrutinize where exactly we are in this pandemic.

Epidemiology of COVID-19

It seems that coronaviruses take an important place in the 21th century history. Five of seven human coronavirus was isolated in this century. Unfortunately, last three of them entered our life with a fear of outbreak, pandemic or death. Last human coronavirus which emerged world from Wuhan China, SARS CoV-2 and its clinical expression, Coronavirus disease (COVID-19) recently taken a significant place in our daily practice. Initial reports showed that, its origin was bats. It transmitted human to human by droplet and contact routes, but some doubt about airborne, fecal or intrauterine transmission also should be removed. Its R0 value is 2.3 but it could be as high as 5.7. Its case fatality rate was 6.3, but it was different in different ages and counties, and it could be over 15%. According to early models total 10­12 weeks is required to control an outbreak in the community. While different countries show different daily case numbers, total number of case, case mortality rates or R0, it seems they show a similar epidemic curve. Every day we learn new data about the current outbreak. Since the outbreak is not over yet, every detail should be evaluated carefully and the updates should be followed closely to monitor the epidemiological properties of COVID-19.