Two days of new 305 confirmed cases, it is difficult to clear zero before the Spring Festival, why did the epidemic in Xi'an come to this point

On December 26, 150 cases were confirmed in Xi'an in a single day;

On December 25, 155 cases were confirmed in Xi'an in a single day.

Since Wuhan was cleared, no mainland city has been diagnosed with more than 100 cases in a single day. And that's far from the end.

At a press conference yesterday afternoon, it was mentioned that "nucleic acid screening in the next few days may also have a high number of reported cases".

"The current epidemic situation in Xi'an is still running at a high level," a number of experts interviewed told Eight Point Jianwen that to see the inflection point, "it is estimated that at least 10 rounds of nucleic acids will be needed."

Image from Visual China

At present, xi'an's full nucleic acid has been carried out for four rounds, and the fifth round is about to begin.

At midnight on December 23, the city with a population of tens of millions pressed the pause button, and the districts and units in Xi'an implemented closed management, and all residents did not go out unless necessary.

At 18:00 on December 26, Xi'an decided to carry out a city-wide comprehensive eradication. This is the largest city-wide massacre caused by the epidemic after Wuhan.

This city was once the "whistleblower" of the cumulative diagnosis in October this year, which broke through 100 and affected the northwest epidemic in 21 provinces.

Here, almost the strictest epidemic prevention measures in the country have been implemented - all foreigners returning to Xi'an from the province are required to provide a 48-hour certificate of negative internal nucleic acid test. It was this measure that allowed it to almost keep the epidemic from Inner Mongolia out of the city in October this year.

Today, however, a strain similar to the last time, through a route that we still don't know, passes through the airport and directly into the city's most prosperous core, universities, restaurants, hospitals and residential areas... These important places of urban life have become the places where the virus spreads.

Only two months before and after, such a huge gap. Why did the epidemic in Xi'an come to this point, and where will it go?

Why did a single city add more than 100 in a single day?

When the number of new confirmed cases in Xi'an fell briefly on the 23rd, many views believed that the inflection point of the epidemic in Xi'an had appeared, but in the next three days, it ushered in an explosive growth: 75 cases, 155 cases, 150 cases.

It is particularly noteworthy that of the 155 new patients on the 25th, 56 were found in nucleic acid screening, and 7 were actively seeking medical treatment, which shows that after four rounds of large-scale nucleic acid testing, there are still out-of-sight infected people - which also means that the epidemic is still spreading.

The international flight that triggered the xi'an epidemic entered on December 4, and the first case was found on the 8th and confirmed on the 9th, and in the ten days since, the new cases in Xi'an News have not broken through 10, until December 18, when the joint prevention and control mechanism of the State Council reported that the gene sequencing of the cases in Xi'an, Shaanxi and Dongguan, Guangdong, was highly homologous, and the same chain of transmission from the same source of import from abroad - which means that the virus has been spreading in Xi'an for nearly two weeks.

In these two weeks, there were only 3 infected people on the transmission chain of Guo Mou, the staff of the isolation hotel and the outpatient pharmacy who was first diagnosed, but it is obvious that what is more representative of the actual situation of the epidemic in Xi'an is a headless transmission chain: the super transmission chain centered on a family of Liu of Chang'an University who did not know where to infect continued to extend to more than 60 people.

Virologist Chang Rongshan pointed out that the virus that flowed into various districts of the city from Flight PK854 on December 4 will not be limited to the three chains of transmission that have been found, and there is a high probability that there are unknown chains of transmission.

But what is more difficult is that, like Guo, there are more than 100 cases of infection for unknown reasons in the form of headless transmission points, they either take the initiative to come to the sampling point for testing and be exposed, or because of fever to go to the outpatient clinic and be diagnosed, and the trajectory of these unnoticed infected people has spread throughout hundreds of places in xi'an central urban area, such as universities, primary and secondary schools, restaurants, pharmacies, communities, and industrial parks.

"Under the premise that the virus has spread and has been spread for four or five generations, it is almost impossible for the flow to catch up with the speed of the spread of the epidemic", virologist Chang Rongshan told Eight Point Jianwen, the three headless and intersecting transmission chains chased by the flow tune are obviously not comparable to the actual scale of the epidemic, "The flow tune itself has lost its meaning and its role is very limited."

At this time, for a large city with a population of tens of millions, the only way to clear zero is to test nucleic acid for all employees with fast accuracy.

On December 18, when 13 confirmed cases had been found in Dongguan, the second drop point of the epidemic, and five rounds of nucleic acid testing had been carried out in Dalang Town, the main epidemic area, Xi'an began the first round of nucleic acid testing for all employees - which was the key to the final victory of Guangzhou, Qingdao, Wuhan, Harbin and other cities with a population of 10 million people and outbreaks.

On December 23, according to the "China Discipline Inspection and Supervision News", the Xi'an discipline inspection and supervision department found in 15 rounds of inspection and inspection that individual units had problems such as poor nucleic acid testing organization, untimely sample delivery, inaccurate scheduling of testing samples, and untimely control of isolated personnel in some areas.

Jin Dongyan, a virologist at the University of Hong Kong, told Eight Point Jianwen that the nucleic acid test is to find positive in a large number of negative samples, which is very easy to overlook, and once the diagnosis is missed, it means that an unexpected new transmission has begun.

Therefore, since the 18th, Xi'an has begun round after round of uninterrupted large-scale nucleic acid testing to digest the stock.

The premise of chasing stock is that the use of control to reduce the increment, an epidemiologist told Eight Point Jianwen that missed detection is likely to make multiple rounds of nucleic acid testing that has been carried out in place, for example, an infected person in area A after doing a nucleic acid test missed test, and then freely moved to other urban areas that have completed nucleic acid testing to cause the epidemic, and finally returned to area A, which means that the nucleic acid testing work in the two urban areas is all zero, which is for the large-scale epidemic that occurred in the central urban area of Xi'an. It is a real problem that must be considered.

According to the analysis of the above-mentioned epidemiologists, the initial control was not in place, the depth of nucleic acid testing was not enough, and the interval between nucleic acid testing in some areas was too long to make the new transmission possible, and these comprehensive factors made it possible for a period of time to actually put out the fire in the open place and spread in the dark place.

Until the 22nd, after the discovery of a number of positive cases outside the sealed control area caused community transmission, Xi'an began to comprehensively upgrade control and implement closed management of the city's communities, 3574 schools in the city were suspended, non-essential places were temporarily suspended, and non-essential places were required not to leave the city, and Xi'an entered a "lockdown" stage similar to Wuhan.

All nucleic acid 10 rounds of jumping, it is difficult to clear zero before the Spring Festival

On the 18th day after the outbreak, Xi'an began to adopt the "thunderous means" of approaching the lockdown.

At the press conference on the 26th, the Standing Committee of the Xi'an Municipal Party Committee and the member of the Party Group of the Municipal Government explained that "most of the new cases were infected before the upgrading of prevention and control measures, and the rapid discovery of new cases is the effect of the dual role of Xi'an Sealing and Control and Large Screening."

However, as for how deep the bottom of the epidemic is and how large the stock is, it is still unknown. He Wenquan reminded that "nucleic acid screening in the next few days may also have a large number of reported cases".

Jin Dongyan, a professor of virology at the University of Hong Kong, also said that according to the development law of the epidemic in other regions before, the transmission chain currently found in Xi'an is like the "tip of the iceberg".

Finding out the bottom line has become a top priority. And until the mapping is complete, there is no better way for the city than to upgrade prevention and control measures to minimize the movement of people.

In the past week, Xi'an has carried out round after round of city-wide screening: since the first round of nucleic acid test results covering a total of 1566.17 people was announced on December 21, two more rounds have been completed, and the fifth round is currently being carried out.

But Xi'an has not yet ushered in the inflection point of the epidemic, and until then, large-scale screening will continue.

Jin Dongyan told Eight Points That it was impossible to complete the mapping in one fell swoop. This aspect is related to the scale of the current round of epidemics, Xi'an has a huge population, and the epidemic has spread to a certain extent. On the other hand, it is determined by the characteristics of the virus, "even if the infection caused by the same transmission event, it will take a long time to turn into a case, so it is not enough to test only two or three rounds." ”

Wei Xiaoli, deputy director of the Xi'an Municipal Center for Disease Control and Prevention, also mentioned at the press conference on the epidemic on December 25 that the depth, location and duration of throat swab collection may affect the accuracy of the results. Missed tests caused by irregular sampling techniques are also one of the reasons why multiple rounds of screening are required.

How long until the xi'an epidemic has reached an inflection point? In Jin Dongyan's view, the high vaccination rate is a reason for optimism, but the Xi'an epidemic may need to be at least 10 rounds of large-scale screening to be known.

Chang Rongshan believes that according to the current development trend, the epidemic may continue for more than 20 days, and after reaching dynamic clearance, it will take about a week of observation and stabilization to completely unseal.

This will undoubtedly bring more uncertainty to the upcoming Spring Festival. As a transportation hub in the northwest, Xi'an sent more than 20 million passengers during the Spring Festival in 2020. However, the 2022 Spring Festival will open on January 17 in three weeks, when Xi'an is still at the risk level of "can't pass", and most traffic operations in the northwest region will face challenges.

In the face of the next stage, Jin Dongyan believes that Xi'an has been sealed and controlled by "thunder" means, but in view of the hidden nature of the virus, other parts of the country cannot relax their vigilance and need to strictly prevent the further spread of spillover cases.

In addition, the recent surge in foreign epidemics and the strong spread of the new mutant strain omicron will be the most severe test of "external defense import" in more than a year. Chang Rongshan specifically mentioned that existing studies have shown that the omicron variant strain is more likely to "penetrate" the existing physical prevention and control system, and as the proportion of omicron in overseas confirmed cases soars, the imported risk multiplies, and the flow adjustment will be extremely difficult, and it is difficult to accurately prevent and control the "critical period" of the previous week. He suggested that respiratory samples of all personnel leaving airports with international flights can be retained for 10 days or more every day, and every ten copies are kept in one tube (ten mixed one), not tested, convenient for later traceability, "otherwise once there is penetration, the flow tone has no clue, missing the key first few days, this practice, the cost is not high, and it is half the effort." ″

Yu Huanhuan and Zhang Yuqi | writing

Xu Zhuojun and Li Shanshan | responsible editors

This article was first published on the WeChat public account "Eight Points Health" (ID: HealthInsight)

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