Journal of Medical Virology

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2, has spread worldwide triggering a pandemic. Its first case was reported in Wuhan, the capital of China's Hubei province, and since then it has spread across the world becoming one of the worst pandemics in the history of mankind.1 Its basic reproductive number (R0) has been determined to be 2 to 3.2 Here, the basic R0 is the average number of secondary cases generated by infected subjects in the completely susceptible population. Any pandemic with a basic R0 less than 1 will die out on its own.3 To give a perspective to this number, the 1918 influenza pandemic which infected one-third of world's population and resulted in 50 million casualties had an R0 of 1.8.4 Majority of patients with COVID-19 show mild symptoms and recover on their own in 2 to 3 weeks, so it is likely that cases could go undetected and the actual basic R0 is much higher than stated above. COVID-19 symptoms include fever, cough, sore throat, diarrhea, shortness of breath, loss of smell/taste, and pneumonia, and in severe cases, it can lead to multiple organ failure and death.5 The overall rate of mortality per confirmed cases has been reported to be nearly 4.5%.6 The rate of recovery and severity of the disease depends on the age and health of the subjects. The younger age group without any prehealth condition is expected to have a low death rate (0.2%), whereas the older population (above 80) have much higher death rate (15%).6 Research is being carried out for validating the available potential treatment regime and vaccines, and for developing a new one. As described before, R0 = 2-3 as per recent reports. If R0 = 2, then Y = [(2 − 1)/2] × 100 = 50%. Similarly, when R0 = 3, then Y = [(3 − 1)/3 × 100 = 66.66% Therefore, for R0 = 2-3, nearly 50% to 66.66%* (threshold) of the population is required to be immune against COVID-19 for the protection of susceptible individuals in a given population through herd immunity. *As discussed previously, it can ...

COVID‐19: Herd immunity and convalescent plasma transfer therapy