Does XBB change the main organs of infection? 6 questions about Omicron "XBB"...

Recently, the new coronavirus variant XBB has been detected in Shanghai, Hangzhou and other places. Due to its improved immune escape ability, this branch variant has become the dominant epidemic strain in some European and American countries.

XBB has attracted widespread attention. Recently, it was reported online that XBB mainly attacks the digestive system and is prone to cause diarrhea, etc., and even triggered a stockpiling trend of drugs such as montmorillonite powder.

On January 3, the reporter contacted several public health and infectious disease experts to answer questions about the prevalence of XBB, the time window for reinfection, and the main organs affected.

1. What kind of virus is XBB? How many variants does it have?

According to information from the World Health Organization, XBB is a recombinant of the Omicron variants BA.2.10.1 and BA.2.75.

Sun Yamin, a professor at the Institute of Public Health and Health of Nankai University, told reporters that if a certain type of mutated new coronavirus causes a small-scale epidemic in a certain place, it will be defined as a variant. At present, there are 14 defined sub-variants of XBB, including XBB.1, XBB.1.5, XBB.2, XBB.3, etc.

2. How widespread is the prevalence of XBB? Which regions in my country have reported relevant data?

Sun Yamin introduced that XBB was previously prevalent in India and Singapore, but is now spreading in Europe and the United States. In some states in the United States, the prevalence of XBB.1.5 is growing rapidly. Some scientists believe that XBB.1.5 has quickly replaced BQ.1.1 and BQ.1 to become the number one prevalent strain in the United States.

Data retrieved from international databases showed that as of December 28 last year, 84 countries and regions had isolated variants and sub-variants of XBB.

In my country, Shanghai recently announced that it had detected 25 cases of XBB, including XBB.1.5, which did not cause local transmission; Hangzhou announced today (January 3) that XBB, BQ.1, BQ.1.19 and other Omicron evolutionary branch virus strains were detected among inbound personnel under closed-loop management. It can be retrieved in the database that XBB has also been found in Jiangsu.

However, Sun Yamin said that XBB is not yet the main epidemic strain in my country, and the cases in these cities should all be imported from abroad.

3. Does XBB spread faster and be more virulent than other variants?

The reporter consulted an infectious disease expert who has been treating COVID-19 patients on the front line for a long time. He replied that current international research reports on XBB show that the variant has stronger immune escape and spreads faster, but has not been found to be more virulent.

Sun Yamin told reporters that for each branch of Omicron, the natural selection pressure is not virulence, but immune escape. The original ability of the virus to spread depends on its binding to cell receptors. At a time when most people in the world have been infected with the new coronavirus, the ability to spread is actually the ability to escape immunity. Only with the ability to infect the infected population can it continue to spread. This is also the advantage of XBB.

4. Will XBB trigger a new round of pandemic?

Sun Yamin said that to analyze whether a variant strain has caused an epidemic, the history of infection of the population in a certain area must be considered. Even internationally, XBB has not caused a full-scale pandemic. In the United States, XBB.1.5 is highly prevalent in some states, but in nearby Canada, the strain has not yet entered the top five mainstream variants and seems to be in the accumulation stage.

In my country, it is unlikely that XBB will cause a large-scale epidemic in the short term, because the general antibody level of the population is still high. After a few months when the antibody level drops, the possibility of reinfection increases, but the variant strain that is prevalent at that time may not be XBB.

5. Will XBB shorten the secondary infection window?

It is generally believed that between 3-6 months after infection with the new coronavirus, due to the high antibody level, even if the virus has the ability to escape immunity, the chance of secondary infection will be reduced. Is it possible for XBB to shorten the time window?

"Suppose I have just been infected and my antibody level is 100%, which will drop slightly after two months. But if the new variant escapes the antibodies produced by several major antigenic determinants, the combined effects of the two may shorten the infection cycle." Sun Yamin analyzed, but this conclusion requires statistics on the time of secondary infection, and no relevant reports have been seen so far.

6. Has the mutant changed the pathogenic site? Should I stock up on montmorillonite powder?

Recently, it was reported online that XBB's main target organ has shifted to the digestive system, which can easily cause diarrhea. Influenced by this, many netizens began to stock up on drugs related to digestive system diseases such as montmorillonite powder.

An expert from the infectious disease department of a tertiary hospital in Beijing said that from the beginning, the novel coronavirus can cause more than a dozen symptoms, including diarrhea, nausea and vomiting, decreased taste and smell and other digestive system symptoms. The non-XBB variants such as BF.7 and BA.5.2 currently prevalent in Beijing have also been observed to cause diarrhea in patients clinically. "It can only be said that when the number of infections was relatively small, some symptoms were not observed. Now that they have become more common, most of the symptoms have occurred."

Sun Yamin introduced that, taking the latest XBB variant XBB.1.5 as an example, its mutation site is in the RBD region, and its function is to evade immunity, while the path of the virus invading the human body through ACE2 has not changed. ACE2 is a cellular attribute, not unique to a certain organ, which is one of the reasons why the new coronavirus can affect many organs of the human body since the original strain. Based on the existing information, the possibility that "XBB is more likely to invade the digestive tract" is not particularly high.

Li Dongzeng, chief physician of the Department of Respiratory and Infectious Diseases at Beijing You'an Hospital, also said in an interview with the media that drugs for treating respiratory and digestive tract infections in response to the new coronavirus can be prepared appropriately and there is no need to stockpile them in large quantities.

(Source: Beijing News)