Is the old strain of COVID-19 "reappearing" in my country? Experts talk about 3 truths

Science and Technology Daily reporter Zhang Jiaxing

Recently, there have been rumors that the number of severe cases and deaths from COVID-19 has increased because the new coronavirus prevalent in northern my country is not only the Omicron strain, but also "old strains" such as the Delta strain and even the original strain.

Some people believe that lung infection is caused by "old strains" based on the fact that "Omicron does not invade the lungs"; there are also rumors speculating that the new coronavirus is lurking in my country without mutating, and even mistakenly citing data from the Chinese Center for Disease Control and Prevention that found more than 130 mutant branches, and saying that the Omicron branch is Delta.

Is it possible that the "old strain" of COVID-19 has resurfaced? In response to the above rumors, Science and Technology Daily interviewed relevant experts online to hear what they had to say.

Truth 1: People with severe symptoms were monitored closely, and no “old strains” were found

"Through whole genome sequencing, our country has never interrupted its monitoring of domestic epidemic strains." Tong Yigang, a virology expert and dean of the School of Life Sciences and Technology at Beijing University of Chemical Technology, told Science and Technology Daily that whole genome sequencing technology can sequence more than 30,000 bases of the new coronavirus one by one, conduct bioinformatics analysis based on the sequencing results, and then classify different variants into corresponding subtypes.

"The new coronavirus strains that infect people with severe symptoms are actually the focus of monitoring." Tong Yigang said that monitoring is "focused" on severe cases. If severe cases are really caused by "old strains", they will be monitored at the first time. Now there are no severe cases, which means that they are not caused by "old strains".

Image source: National Center for Bioinformation 2019 Novel Coronavirus Information Database

In order to grasp the dynamics of some highly pathogenic epidemic strains as soon as possible, disease control departments will mostly sample and sequence strains that cause severe illness. According to the currently implemented "Work Plan for Monitoring Variants of New Coronavirus in the Chinese Population", each province in my country selects three cities to set up a sentinel hospital, collect specimens from 15 outpatient emergency cases, 10 severe cases and all deaths every week for genome sequencing and analysis, and upload the sequencing data to the China Center for Disease Control and Prevention within one week.

"It's not just in Beijing. No Delta strain or original strain has been found in the entire country." Tong Yigang checked the relevant database and told Science and Technology Daily that thousands of sequencing data monitored by the Chinese Center for Disease Control and Prevention in recent times showed that there was no Delta strain or original strain.

Xu Wenbo, director of the Institute of Viral Diseases at the Chinese Center for Disease Control and Prevention, also said that in the past three months, my country has monitored the introduction of BF.7, BQ.1, and XBB into my country, with a total of more than 130 subbranches of Omicron imported into my country. It can be seen that despite the large number of subbranches, they are all variants of Omicron, and no other "old strains" have been found.

Fact 2: Omicron may also cause pneumonia

"No study has ever confirmed that Omicron only infects the upper respiratory tract or does not cause severe illness. Even if the influenza virus mainly infects the upper respiratory tract, it can cause pneumonia in some people." Tong Yigang said that the current clinical situation shows that the pathogenicity of Omicron is weaker than the previous epidemic strains.

But people still feel that the situation caused by Omicron infection is much more serious than expected. Why is that?

Tong Yigang believes that the main reason is that my country has a large population base. Even if the severity and mortality rates are very low, the absolute number is still large. On the other hand, people receive a large amount of local information in a short period of time from WeChat and other communication media, and they will mistake the local situation for the overall situation, and then there is some exaggeration in their perception.

In addition, there are also deviations in the understanding of some severe symptoms that have led to exaggeration. Jiao Yahui, director of the Medical Administration Department of the National Health Commission, corrected people's misunderstanding of "white lung": white lung is a more serious manifestation of pneumonia, and the white image area can reach 70%-80%, and the proportion of such patients is very low. Not all inflammation in the lungs is called white lung, and not all white lungs mentioned on the Internet are real white lungs.

Truth 3: In a competition between virus variants, the one with the advantage of transmission wins

So, is it possible that remnants of the original strain have not been cleared and have just happened to go undetected? Or is Omicron returning to a more virulent strain?

"It is true that the virus mutation is directionless. During the virus replication process, random mismatches of the genetic code occur, which in turn trigger mutations." Tong Yigang said, but whether this mutation can be preserved depends on whether it can bring a transmission advantage to the virus, and this advantage is the direction of evolution.

Tong Yigang further explained, imagine that if there are two different strains, Omicron and Delta, spreading in the same place at the same time, the one with faster transmission and stronger infection ability will definitely replace the other. This is like playing Go. The white side (Omicron) can move 10 pieces each time, and the black side (Delta or original strain) can move 1 piece each time. It won't be long before there are only white pieces left on the board.

The evolution of the new coronavirus due to its transmission advantage has been confirmed many times around the world. The new coronavirus evolved from the original strain to the alpha strain and then to the delta strain, and then Omicron became the mainstream strain, and there were continuous iterations between sub-branches, all because the virus strain has the advantages of rapid transmission and immune escape.

An expert in the field of bioinformatics data cited a series of global COVID-19 monitoring data and told Science and Technology Daily: " From our statistics, the Delta strain has basically disappeared worldwide since late March. "