Estimates on new positive persons for Omicron variant (Tokyo) #2

・We compared the number of new positive cases against both infectivity of the Omicron variant and the start of the 3rd vaccination in Tokyo.

・If the infectivity of the Omicron variant is assumed to be equivalent to the average of January 1 to 6, and if the 3rd vaccination is administered within 240 days to those who vaccinated, the number of new positive cases could reach about 50,000 persons per day in early March.

・Controlling the number of people staying out at night to 70% could reduce the number of new positive cases to 28,000 per day, and reducing it to 50% could reduce new positive cases to 16,000 per day.

・The number of seriously ill patients was estimated to range from 570 to 290 per day. However, these values are for reference due to lack of data.

・Effective control measures are as below.
　・Reduce the number of people staying out at night by 50%
　・Booster vaccination for the elderly 180 days after the 2nd vaccination
　・Because of the rapid spread of infections, the effect is small in the short term of shortening the number of days elapsed for vaccination of people under 60 years of age.

Comparison of the Delta and Omicron variants with 3rd vaccination

If the infectivity of the Omicron variant is assumed to be equivalent to the average of January 1 to 6, and if the 3rd vaccination is administered within 240 days to those who vaccinated, the number of new positive cases could reach about 50,000 persons per day in early March.
Controlling the number of people staying out at night to 70% could reduce the number of new positive cases to 28,000 per day, and reducing it to 50% could reduce new positive cases to 16,000 per day.

Booster vaccination period: 7 months after vaccination for ages 60 and over, 8 months after vaccination for ages under 60.
Efficacy of 2nd vaccination for preventing infection: 33%
Efficacy of 3rd vaccination for preventing infection: 75%
Rate of 3rd vaccination: 90% (rate among people with 2nd vaccination)
Remaining population: Downtown at 21:00, average of December 2021

The number of seriously ill patients is estimated to be around 600 under the most pessimistic scenario (no human flow control).
Even in the optimistic scenario (50% human flow control), the number of seriouslyill patients is expected to be around 300, which is about the same as last summer.
*However, these values are for reference due to the lack of data.

Booster vaccination period: 7 months after vaccination for ages 60 and over, 8 months after vaccination for ages under 60
Efficacy of 3rd vaccination for preventing infection: 75%
Rate of 3rd vaccination: 90% (rate among people with 2nd vaccination)
Remaining population: Downtown at 21:00, average of December 2021
Number of seriously ill patients: 0.1 times compared with the Delta variant (taking into account hospitalization rate, decline rate, and oral medications)

If booster vaccination of the elderly was conducted after 180 days (6 months), the number of new positive cases could be reduced to about 12,000 and the number of seriously ill patients to about 200 during the peak period.

Booster vaccination period: 6 months after vaccination for ages 60 and over, 8 months after vaccination for ages under 60
Efficacy of 3rd vaccination for preventing infection: 75%
Rate of 3rd vaccination: 90% (rate among people with 2nd vaccination)
Remaining population: Downtown at 21:00, average of December 2021
Number of seriously ill patients: 0.1 times compared with the Delta variant (taking into account hospitalization rate, decline rate, and oral medications)

1.Infection model by SEIR mathematical model and AI optimization method
The SEIR model, which takes into account population flow and AI technology (evolutionary optimization + quasi-Newton method), were used to optimize infection model estimation within and between three age groups (0-39 years, 40-59 years, and 60 years or older). The number of positive patient inflows from outside the prefecture was estimated from mobile spatial statistics data (NTT Docomo) and LocationMind xPop*1 and incorporated into the model, and the model was trained from data from March 1 to October 30, 2021.

2.Effects of vaccine and behavior change 　・Vaccine efficacy was 33% for the 2nd and 75% for the 3rd dose against the Omicron variant. The Omicron variant was assumed to have started to infect 5 people via community spread on December 10.
　・Measured values are used for changes in the effective reproduction number and the number of populations flows from March 1 to December 18. The effective reproductions number and risk of inflow of infected persons were estimated assuming that the population remaining in downtown areas (13:00, 19:00, and 21:00) and the population coming from outside Tokyo were at the same levels as in November after December 19.
　・Diminishing vaccine efficacy was assumed to diminish to 50% in 180 days. Booster vaccinations were to begin on December 1 for medical personnel 180 days after the 2nd vaccination, 210 days after January 15 for the elderly, and 240 days after February 1 for those under 60 years of age.
　　・httpss://www.gov.il/en/departments/news/05072021-03, httpss://www.gov.il/en/departments/news/06072021-04
　　・Resurgence of SARS-CoV-2 Infection in a Highly Vaccinated Health System Workforce, DOI: 10.1056/NEJMc2112981, The new England journal of medicine
　　・COVID vaccines protect against Delta, but their effectiveness wanes, doi: httpss://doi.org/10.1038/d41586-021-02261-8, Nature
　　・Comparative Effectiveness of Moderna, Pfizer-BioNTech, and Janssen (Johnson & Johnson) Vaccines in Preventing COVID-19 Hospitalizations Among Adults Without Immunocompromising Conditions — United States, March–August 2021, CDC vol.70, 17, Sep. 2021
　　・National Institute of Infectious Diseases, Mutated variant B.1.1.529 (the Omicron variant) of SARS-CoV-2 (5th report), 2021

3.Tokyo suburbs agent base model
We constructed a model represented by 1,348 agents in 2 cities based on the household structure of a Tokyo suburb, and restricted workplaces, restaurants, and event venues by vaccination proof, and measured the rate of change in Rt from 500 trials each. Companions to eat and drink together were assumed to be chosen randomly from a network of friends (the number of friends was a power-law distributed Galton-Watson network).

*1 "LocationMind xPop" data is data that NTT DOCOMO collectively and statistically processes from mobile phone location information sent with permission from users of applications* provided by NTT DOCOMO. Location information is GPS data (latitude and longitude information) that is measured at a minimum of every five minutes, and does not contain information that identifies an individual. DOCOMO Map Navi Service (map application, local guide) and some other applications