Prevention of infection per population by the third vaccination scenario

Based on the medium model (infection-prevention effects of the 1st and 2nd vaccinations: 65% and 75%, respectively) and the report on October 5, it is assumed that the prevention effect of the 3rd vaccination will be 95% and the attenuation rate of the prevention effects of the 2nd and 3rd vaccinations of half a year later will be 35% and 55%, respectively (decrease linearly). The vaccination effect is assumed to keep its peak for 14 days after vaccination and then attenuate (Reference: https://doi.org/10.1038/d41586-021-02261-8).：https://doi.org/10.1038/d41586-021-02261-8）。

(Reported at the AI periodic meeting of the Cabinet Secretariat on October 5)
Decrease in the prevention effect of the second vaccination. The prevention effect of the third booster shot on the delta variant was estimated to be 95%
The attenuation effect was also estimated as in the left figure
10/21　Pfizer reported that it was 95.6%

https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-announce-phase-3-trial-data-showing

First/Second Cabinet Secretariat COVID AI simulation material (medium model)
Zeng B, Gao L, Zhou Q, Yu K, Sun F. Effectiveness of COVID-19 vaccines against SARS-CoV-2 variants of concern: a systematic review and meta-analysis. medRxiv. 2021.
Aran D. Estimating real-world COVID-19 vaccine effectiveness in Israel using aggregated counts. MedRxiv. 2021.

Effectiveness of infection prevention per capita

From now on, the effectiveness of infection-prevention vaccination per capita will decrease
What is the threshold at which it may start to increase in Japan?

Japan (upper) What is the threshold? Depends on the new normal and countermeasures against infection

Israel (right): (Blue dotted line) Comparison is difficult for the original variant, but infection starts to decrease when the proportion of vaccinated people in the population exceeds 20% (the elderly account for 10%). (Green dotted line) For the delta variant, the effective rate per capita is about 30% *Drastic decrease from early September

*For the delta variant. The prevention effect of January is different from the actual one

１．For cases where the third vaccination is assumed to be conducted
　1. six months later
　2. seven months later
　3. eight months later
　4. and nine months later
　　respectively, after the second vaccination, made trial calculations of the effectiveness of infection prevention per capita (assuming that all applicable people are vaccinated)

Assumed the timing at which to start the third vaccination is December 1, and allocated the number of people who were vaccinated before that date, assuming such number will increase immediately as shown in the following table. (Second vaccination: Started on 2021/3/10 in Tokyo and 2021/3/11 in Osaka and Aichi)

2．Assume that the third vaccination is to be conducted eight months after the completion date of the second vaccination (in the case of 3 above).
　1. 100％
　2. 80％
　3. 70％
　4. 60％
　　Made trial calculations of the effective proportion of infection prevention per capita assuming that the said proportions of the applicable people seek vaccination:

Assume the timing at which to start the third vaccination is December 1 and the date of the third vaccination is eight months after the completion date of the second vaccination, and assume the number of vaccinated people on the corresponding date before it will increase immediately after the start. It is assumed that all applicable people are vaccinated.

Age is considered
Based on the report that the effectiveness of the second vaccination is 72% for people aged 60 or older and 78% for people younger than 60(https://www.medrxiv.org/content/medrxiv/early/2021/02/19/2021.02.05.21251139.full.pdf)に基づき、
(Age is considered 1)
Aged 0–59: The effectiveness of the second and third vaccinations is 72% and 92%, respectively
60 or older: The effectiveness of the second and third vaccinations is 78% and 98%, respectively
(Age is considered 2)
Aged 0–59: The effectiveness of the second and third vaccinations is 72% and 89%, respectively
60 or older: The effectiveness of the second and third vaccinations is 78% and 95%, respectively
Calculated the population-level vaccination effectiveness assuming that the decline rate is the same

Assume the timing at which to start the third vaccination is December 1, and assume the number of vaccinated people on the corresponding date before it will increase immediately after the start. (Start date of the second vaccination: Tokyo from 2021/3/10 and onward.)

Assume the timing at which to start the third vaccination is December 1, and assume the number of vaccinated people on the corresponding date before it will increase immediately after the start. (Start date of the second vaccination: Tokyo from 2021/3/10 and onward.)

Assume the timing at which to start the third vaccination is December 1, and assume the number of vaccinated people on the corresponding date before it will increase immediately after the start. (Start date of the second vaccination: Osaka from 2021/3/11 and onward.)

Assume the timing at which to start the third vaccination is December 1, and assume the number of vaccinated people on the corresponding date before it will increase immediately after the start. (Start date of the second vaccination: Aichi from 2021/3/11 and onward.)

Assume the timing at which to start the third vaccination is December 1, and assume the number of vaccinated people on the corresponding date before it will increase immediately after the start. (Start date of the second vaccination: Osaka from 2021/3/11 and onward.)

Assume the timing at which to start the third vaccination is December 1, and assume the number of vaccinated people on the corresponding date before it will increase immediately after the start. (Start date of the second vaccination: Osaka from 2021/3/11 and onward.)

Relationship between the effective reproduction number and the vaccination rate/vaccination effectiveness in Tokyo, Osaka, and Aichi

Corrected the effective reproduction number to keep flows of people constant (-25%) based on the approximated straight line (about 5% lower if 2 weeks earlier)

・Derived the effective proportion of the infection-prevention effect per capita based on the temporal transition in the average infection-prevention effect of individual persons
　(Verification of Israel)
・In Israel, the threshold at which the effective reproduction number for the delta variant is 1 or less is the effectiveness of the infection-prevention effect per capita of 30% of the level of flows of people between August and September 2021.
・(For the delta variant) Fell below for a little longer than two months from mid-June to the end of August in 2021, and infection spread and then the situation improved thanks to a booster shot (one interpretation).
　(Trial calculation in Japan)
・Though the third vaccination was started eight months later, the effective proportion of the prevention effect could be kept at 35% for several months.
・If a certain proportion of people vaccinated twice do not receive the third vaccination, the disease may spread around Golden Week (GW, a series of holidays in April and early May) (depending on behaviors).
・The threshold in Japan is about 30% during the declaration of a state of emergency (August 2021). An increase in flows of people and behavior changes raise this threshold. Since behaviors also change, the threshold changes every day. (Analysis and approximation based on scenario settings are possible.)

Issue
・Not the data for Japanese people
・Detailed planning support with high accuracy and prediction using data considering age correction (third vaccination interval based on the age, etc.)
・Need to focus on the trend of Israel after the third booster shot (possible by analysis using AI for the decline rate of the prevention effect).