China News Service, April 2nd. The State Council's joint prevention and control mechanism held a press conference on the 2nd to introduce the situation of the new crown pneumonia epidemic prevention and control and medical international cooperation. At the press conference, Wu Zunyou, chief expert of epidemiology of the China Centers for Disease Control and Prevention, mentioned an article in the preprint of the Chinese Journal of Epidemiology at the press conference: The study found that on average, each confirmed patient can spread nearly 3 patients, and the average is asymptomatic Infected persons can spread to less than one patient, that is, the transmission efficiency of asymptomatic infected persons is about one third of the confirmed cases.
Reporter asked: At present, the academic circles have different opinions on the transmission of asymptomatic infection. Some media even report that asymptomatic infection may cause a new round of outbreak in China. What do experts think about the transmission of asymptomatic people and its impact on future epidemic prevention and control?
Wu Zunyou said that the preprint of the Chinese Journal of Epidemiology had an article in the previous two days. This research was carried out by the Ningbo Centers for Disease Control and Prevention. They observed close contacts of confirmed patients and close contacts of asymptomatic infection. Look at the incidence in these two groups. This study has two very important hints of public health significance.
First, they found that, on average, nearly three patients can be transmitted per diagnosed patient, and less than one patient can be transmitted on average per asymptomatic infection. In other words, the transmission efficiency of asymptomatic infection is equivalent to about one third of the confirmed cases, which is at the individual level.
Secondly, at the population level, the proportion of cases transmitted by asymptomatic infections to the total number of cases is only 4.4%, less than 5%. Diffusion contribution is relatively small. This is a local study in Ningbo.
Some other provinces have also conducted some investigations. A larger study conducted in a southern province showed that more than 1,500 close contacts of asymptomatic infected persons had 7 cases. However, further investigation and analysis revealed that these 7 people Not only had contact with asymptomatic infections, but also confirmed patients. In other words, it cannot be considered to be caused by an asymptomatic person. If this co-exposure situation is not investigated carefully, it may expand the judgement of the transmission ability of asymptomatic infection. As for asymptomatic infection, the data of infectious period, transmission ability, and transmission contribution are still very limited. More research and observation are needed in order to have a better understanding of this phenomenon.
Wu Zunyou reminded that all asymptomatic infections must have had a history of contact with confirmed patients, or he has been to an endemic area where an epidemic is happening. For areas where the epidemic has occurred but confirmed cases have cleared for more than two weeks, no Sudden asymptomatic infection will occur suddenly for no reason. The current measures should be able to detect and control asymptomatic infections in a timely manner. The possibility of epidemics by asymptomatic infections is very small, and it will not cause the spread at the social level.