The latest forecast of Lanzhou University: This round of local epidemic is expected to infect 35,000 people and be brought under control in early April

Recently, there have been frequent epidemics in many places in China.

Recently, there have been frequent epidemics in many places in China.

According to data from the National Health Commission, from 0:00 on March 1 to 24:00 on March 14, there were 7,241 asymptomatic infections

The preliminary prediction results of Lanzhou University's " New Coronary Pneumonia Epidemic Global Prediction System" show that under the current government's timely and effective control measures (blue solid line in Figure 1) , the current round of the epidemic in the mainland is expected to start in early April 2022.

Preliminary prediction results of the epidemic situation in mainland China in March 2022 (Source: Lanzhou University official website)

Preliminary prediction results of the epidemic situation in mainland China in March 2022 (Source: Lanzhou University official website)

Wu Zunyou, chief expert of epidemiology at the Chinese Center for Disease Control and Prevention, said in an interview that because Omicron is highly contagious, occult, and has mild symptoms, it has increased the difficulty of finding the earliest cases at the first time, which has caused many Several outbreaks occurred at the same time in the province

Wu Zunyou, chief expert of epidemiology at the Chinese Center for Disease Control and Prevention, said in an interview that because Omicron is highly contagious, occult, and has mild symptoms, it has increased the difficulty of finding the earliest cases at the first time, which has caused many Several outbreaks occurred at the same time in the province

According to the prediction of Lanzhou University, China will usher in the peak of the epidemic this week, which is also a turning point

However, in contrast to the global situation, the number of new cases in some neighboring countries and regions of China is still growing rapidly, adding pressure to domestic epidemic prevention

The number of newly confirmed cases in South Korea in a single day has exceeded 300,000 for 3 consecutive days, with a maximum of 380,000; the number of newly confirmed cases in Vietnam has exceeded 160,000 for 6 consecutive days, with a maximum of 450,000; the daily increase in Hong Kong remains unchanged At a high level, according to previous estimates by the University of Hong Kong, up to 4.

Not only that, the emergence of a new variant has shattered the dream of "defeating the epidemic" on a global scale

Recently, the French Pasteur Research Institute said that they have found more than ten cases of variants combining AY.

WHO press conference site

WHO press conference site

So, where exactly does this new variant come from?

So, where exactly does this new variant come from?

Delta Chron is a new hybrid of Delta and Omikron through recombination

Delta Chron is a new hybrid of Delta and Omikron through recombination

This nascent virus has its own genome, can complete replication, and is an independent individual (which can be roughly understood as a child of Delta and Omicron )

On March 9, American scholars published an article on medRxiv, confirming that Delta Chron appeared in the United States, providing evidence of co-infection and recombination of Delta and Omicron, confirming the existence of a new strain

To find Delta Chron, you must first frame the time period when Delta and Omikron coexisted

doi: https://doi.
org/10.
1101/2022.
03.
09.
22272113

doi: https://doi.
org/10.
1101/2022.
03.
09.
22272113

Before December 6, Delta had been the dominant strain, and Omicron had not yet swept the United States; however, in the week after January 17, the Omicron variant grew rapidly, accounting for more than 99% of the total number of cases
.

Before December 6, Delta had been the dominant strain, and Omicron had not yet swept the United States; however, in the week after January 17, the Omicron variant grew rapidly, accounting for more than 99% of the total number of cases
.

Between December 6, 2021, and January 23, 2022, due to the coexistence of the two variants, the possibility of a syncytial variant due to recombination is also greatly increased
.

Between December 6, 2021, and January 23, 2022, due to the coexistence of the two variants, the possibility of a syncytial variant due to recombination is also greatly increased
.

Therefore, scholars focused on analyzing 16,386 sequence data from December 6th to January 23rd
.
Of all the samples collected, there were 20 cases of co-infection of Delta and Omicron, and these samples were mainly concentrated in December last year, when the two variants accounted for a similar proportion
.

Therefore, scholars focused on analyzing 16,386 sequence data from December 6th to January 23rd
.
Of all the samples collected, there were 20 cases of co-infection of Delta and Omicron, and these samples were mainly concentrated in December last year, when the two variants accounted for a similar proportion
.

doi:  https://doi.
org/10.
1101/2022.
03.
09.
22272113

doi:  https://doi.
org/10.
1101/2022.
03.
09.
22272113

When co-infection occurs, some host cells inevitably contain both variants, causing recombination
.
When a recombinant becomes replicable, researchers can detect it from sequencing
.

When co-infection occurs, some host cells inevitably contain both variants, causing recombination
.
When a recombinant becomes replicable, researchers can detect it from sequencing
.

Taking co-infected sample 16 as an example, the allele from the delta (orange) mutation is high at the 5' end of the genome, but to the gene that controls the SARS-CoV-2 S protein (the spike protein, the protein that enables the virus to enter cells ) , declined rapidly and remained at this level until the 3' end
.
And the allele from the Omicron (blue) mutation occupies half of the S gene and the 3' end after it
.

Taking co-infected sample 16 as an example, the allele from the delta (orange) mutation is high at the 5' end of the genome, but to the gene that controls the SARS-CoV-2 S protein (the spike protein, the protein that enables the virus to enter cells ) , declined rapidly and remained at this level until the 3' end
.
And the allele from the Omicron (blue) mutation occupies half of the S gene and the 3' end after it
.

The map shows that in sample 16, there is a recombination between delta and arcane chryon, and the breakpoint is located before S:214EPEins (gray area in the figure)
.

The map shows that in sample 16, there is a recombination between delta and arcane chryon, and the breakpoint is located before S:214EPEins (gray area in the figure)
.

doi:  https://doi.
org/10.
1101/2022.
03.
09.
22272113

doi:  https://doi.
org/10.
1101/2022.
03.
09.
22272113

After determining that co-infection produced a replication-competent virus, the researchers went on to look for samples composed entirely of Delta Chron
.
In the end, the researchers identified 2 cases of recombinant samples, with multiple consecutive delta mutations at the 5' end, and Omicron dominated at the S gene and 3' end
.
However, the breakpoints of the two recombinants are slightly different: the breakpoint of recombinant sample 1 is near S:G339D, and the breakpoint of recombinant sample 2 is near S:T19R
.

After determining that co-infection produced a replication-competent virus, the researchers went on to look for samples composed entirely of Delta Chron
.
In the end, the researchers identified 2 cases of recombinant samples, with multiple consecutive delta mutations at the 5' end, and Omicron dominated at the S gene and 3' end
.
However, the breakpoints of the two recombinants are slightly different: the breakpoint of recombinant sample 1 is near S:G339D, and the breakpoint of recombinant sample 2 is near S:T19R
.

doi:  https://doi.
org/10.
1101/2022.
03.
09.
22272113

doi:  https://doi.
org/10.
1101/2022.
03.
09.
22272113

"Delta Chron is real, and we ruled out contamination and technical artifacts, it's a true recombinant variant,
" the authors explain in the discussion, "but the transmissibility and virulence of this variant is currently It's not clear, and it's very rare
.
"

"Delta Chron is real, and we ruled out contamination and technical artifacts, it's a true recombinant variant,
" the authors explain in the discussion, "but the transmissibility and virulence of this variant is currently It's not clear, and it's very rare
.
"

Maria van Kerkhove, WHO's new crown technical chief, said in an interview that the emergence of this new variant was completely expected, especially under the "heavy offensive" of Omikron and Delta
.
Little research has been done on Delta Chron so far, she added, and her team is tracking the new variant
.

Maria van Kerkhove, WHO's new crown technical chief, said in an interview that the emergence of this new variant was completely expected, especially under the "heavy offensive" of Omikron and Delta
.
Little research has been done on Delta Chron so far, she added, and her team is tracking the new variant
.

References

References

[1] Evidence for SARS-CoV-2 Delta and Omicron co-infections and recombination.
Alexandre Bolze, Simon White, Tracy Basler, Andrew Dei, Rossi, Pavitra Roychoudhury, Alexander, L.
Greninger, Kathleen Hayashibara, Dana Wyman, Eric Kil , Hang Dai, Tyler Cassens, Kevin Tsan, Jason Nguyen, Jimmy Ramirez, Scotty Carter, Elizabeth T.
Cirulli, Kelly Schiabor, Barrett, Pedro Belda-Ferre, Nicole, L Washington, Sharoni Jacobs, Efren Sandoval, David Becker, James, T Lu, Magnus Isaksson, William Lee, Shishi Luo.
medRxiv 2022.
03.
09.
22272113; doi: 

[1] Evidence for SARS-CoV-2 Delta and Omicron co-infections and recombination.
Alexandre Bolze, Simon White, Tracy Basler, Andrew Dei, Rossi, Pavitra Roychoudhury, Alexander, L.
Greninger, Kathleen Hayashibara, Dana Wyman, Eric Kil , Hang Dai, Tyler Cassens, Kevin Tsan, Jason Nguyen, Jimmy Ramirez, Scotty Carter, Elizabeth T.
Cirulli, Kelly Schiabor, Barrett, Pedro Belda-Ferre, Nicole, L Washington, Sharoni Jacobs, Efren Sandoval, David Becker, James, T Lu, Magnus Isaksson, William Lee, Shishi Luo.
medRxiv 2022.
03.
09.
22272113; doi: 

[2] http://covid-19.
lzu.
edu.
cn/info/1113/2477.
htm

[2] http://covid-19.
lzu.
edu.
cn/info/1113/2477.
htm

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