A contagious, unusual pneumonia broke out in Wuhan, China in December 2019. The virus originated from another animal and jumped to humans, and it was named COVID-19. This is similar to the SARS and MERS coronavirus. China has 33,789 confirmed cases and 811 deaths as of February 8, 2020.
The basic reproductive number (R0) is the average number of new infections that will be created by an infectious person. The R0 is an indication of how transmissible a virus is in a population. If R0 is greater than 1, more people will be infected. If R0 is less than 1, the transmission will stop eventually.
The researchers aim to study the reproductive number of COVID-19.
Researchers used 12 studies that estimated R0 between January 1, 2020 and February 7, 2020. They used PubMed, bioRxiv, and Google Scholar.
Initial studies indicated lower R0 values. The values increased and have recently decreased. The data ranged from 1.4 to 6.49, has a mean of 3.28, and has a median of 2.79. The range between the 25th and 75th percentiles is 1.16 (Table 1).
The World Health Organization (WHO) estimates R0 to range from 1.4 to 2.5. The R0 estimates in this study are much greater than estimates by WHO. The difference in R0 estimates across studies could be due to the estimation methods. Stochastic and statistical models produce reasonable R0 values. R0 values from mathematical models are higher on average. This could be because of different modeling assumptions. Recent studies are more reliable because there is more data. Moreover, these estimates can include the effect of interventions. Recent studies estimate R0 to be 2-3.
Researchers estimate SARS to have an R0 of 2 to 5. This value is similar to COVID-19, which is expected due to the similarities in the virus. But, COVID-19 is already more widespread than SARS even with more public awareness and increased intervention. Thus, COVID-19 may be more transmissible than SARS.
This study estimates the mean R0 for COVID-19 to be 3.28. The WHO estimate of 1.95 is much lower. The estimation method and assumptions affect the estimate. There is still not enough data, so estimates are likely biased. Estimation error should decrease with more data. Considering everything, the R0 is likely around 2-3, which is somewhat consistent with the WHO estimate.