Overall summary
- To continue to be confirmed: The infection-prevention effect on the omicron variant may be 60% of that on the delta variant. As of now, the effectiveness of the antibody on the omicron variant (with countermeasures against infection) is about 35%.
- The rise on January 19 and 20 was partly caused by behaviors during three consecutive holidays.
- The trends of “those who require hospitalization, etc.” and “predicted number of hospitalized people” of this group match. After the spread of infection, the control effect on the spread may be limited even if PCR tests increase, so efforts for confirmation need to be continued.
- Considering asymptomatic infected people, there is a possibility of peaking-out between the end of January and early February (optimistic; Assuming that asymptomatic cases are 10 times more likely than newly positive cases).
Consideration of the infection condition in Okinawa(Reposted on 1/17)
Population of Okinawa: 1.46 million
○Those who have acquired immunity
1. From infection
- Number of positive cases of the omicron variant up to 1/17 (approximate): About 16,000.
- If the proportion of asymptomatic infected people and people who reject PCR is a little more than 4.5 times larger: The total number of infected people is 88,000
- Assuming 10 times stronger infectability = About 180,000
Infected people 6% to 12% (Rose by 3–6% per week if the level of infection remains the same)
2. From vaccination
Acquisition of immunity from vaccination (optimistic) (Defined as the value relative to unvaccinated people upon countermeasures against infection)
-> 31%
Total 37% to 43% (At the end of the 5th wave (8/18) = About 40%*)
- The total value may get close to the threshold
*At that time, behavioral restrictions were applied. The difference in the infectability between the omicron and delta variants and the countermeasures against infection taken by people raise the threshold.
Epidemiological study of Japan 3.9 times (95% CI, 3.0–7.0)
Outpatients visiting 14 Tokyo hospitals (eight metropolitan hospitals and six hospitals of the Tokyo Metropolitan Health and Hospitals Corporation) between September 1, 2020 and March 31, 2021
T. Sanada et al., “Serologic Survey of IgG Against SARS-CoV-2 Among Hospital Visitors Without a History of SARS-CoV-2 Infection in Tokyo, 2020–2021,” https://www.jstage.jst.go.jp/article/jea/advpub/0/advpub_JE20210324/_article
Infection-prevention effect of vaccination on the omicron variant in Tokyo (update)
- Infection-prevention effect of vaccination in Tokyo
Excerpted the days when the approximate proportion of the omicron variant exceeds 90% (without considering unknown people)
The ratio of vaccinated people to unvaccinated people is about 4:1. The proportion of people with the effect on the delta variant will become about 60% associated with temporal deterioration.
The infection-prevention effect on the omicron variant is 64.5% of that on the delta variant
There is a possibility of reaching the peak between the end of January and early February (up to Feb. 10).
Impact of the three consecutive holidays (1/8–1/10)
- Spread through long holiday seasons including year-end and new-year holidays
- The peak of the number of infected people increased two to three times due to the four consecutive holidays and Obon (holidays in August) during the declaration of a state of emergency (MHLW ADB material 21/11/9)
- Since the omicron variant started to spread from the year-end and new-year holidays, the holidays have to be considered in order to appropriately evaluate the infectability.
Effective reproduction numbers in Tokyo, Osaka, and Okinawa
Increase in the number of new positive cases associated with the rise in the effective reproduction number in the three consecutive holidays (including the Coming-of-Age Day celebration) (estimate the value of 1/20)
Tokyo: About 30% from the actual value
Osaka and Aichi: About 50%
Okinawa: Cannot be evaluated because the number of tests and the positive ratio reach the effective upper limits
Spread of infection in places other than the four prefectures (example)
The effective reproduction number is about 2. If the generation time of 3 days is corrected (5 days for the delta variant), the effective reproduction number will be about 1.5
Figures: From Toyo Keizai Online
Predicted and actual values among (1) Number of new positive cases, (2) People who require hospitalization, etc., and (3) Number of hospitalized people
Assumptions:
Flows of people and activity level equivalent to those under the current quasi-state of emergency
The infection-prevention effect of the third booster shot is 85% (100,000 per day)
If the number of asymptomatic infected people is small and the infection-prevention effect on asymptomatic infected people is weak, it will be delayed by about one week.
Without considering asymptomatic infected people, peaking-out will be around mid-March.
Current estimate (four times)
Generation time: 1.67 times (3 days) It has to be considered separately
Effective reproduction number: 1.5 times higher than that of the delta variant
Vaccination effect: -40%
*However, the portions involved in the effective reproduction number are the last two items
Prediction example
Depending on the setting of the vaccination effect, the peak will be delayed (one to two weeks) and increase. Not a drastic decrease.
Summary (3)
(1) The speeds of increase in “people who require hospitalization, etc.*” and “number of hospitalized people” match the prediction results of machine learning up to the delta variant (alpha variant) well
(2) The infectability tends to increase and the toxicity (e.g. number of seriously ill patients) tends to decline. In LSTM, it is not set specifically.
(3) For the infectability of the omicron variant, more infected people are estimated due to free PCR tests, etc.
https://www.jstage.jst.go.jp/article/jea/advpub/0/advpub_JE20210324/_article
(4) Hypothesis: The increase in the number of PCR tests may have only a minor impact on the diffusion of the disease after the spread of infection.
