Effect of Antibody Cocktail

Possibility of worsening of the situation due to the diminishing of vaccine effectiveness for preventing infection
・Assuming that the flow of people is maintained at 30% less than the normal level*, and taking into account the diminishing of the vaccine effectiveness for preventing infection, the number of infected people will increase from leveling off.

Remarkable effect of booster vaccination
・If the diminishing of effectiveness can be ignored due to the implementation of third vaccination and if the flow of people is maintained at 30% less than the normal level, the number of infected people will continue to decrease

Risk of returning to normal flow of people
・If the flow of people returns to normal levels, it would lead to a significant increase in the number of infected people, even if the diminishing in vaccine effectiveness could be ignored

・The normal level refers to the pre-COVID-19 period.
“The flow of people at 30% less than the normal level” indicates the level of people flow as of mid-September 2021.

＜Overview＞
Discussed the effect of antibody cocktail on the spread of infection.

＜Results＞
Under the current administration of doses, the number of deaths has decreased to a certain extent.
If administration is restricted to those with underlying disorder: Death toll will further decrease
If the number of total doses increases: Death toll will further decrease
・No significant effect on slowing the increase in the number of patients with moderate or serious illness

＜Implications＞
1.In the current situation where the supply is limited, administration only to those with underlying diseases contributes to decreased deaths
2.Increased supply of antibody cocktails would further reduce deaths
3.Even if the supply volume increases, the effect of easing bed strain may be limited

・Model for Tokyo based on "Relaxing behavioral restrictions following the spread of vaccination" (released as COVID-19 AI & Simulation Project on August 24)
・Individual attributes: age, gender, industry, occupation, frequency of eating out, history of underlying diseases (added this time)
・Individual probability of infection and serious illness determined by age (in 10-year increments) and history of underlying diseases
・Situations of in person contact: homes, schools, workplaces, facilities for the elderly, restaurants, and other contacts with unspecified number of persons

・Chiba, Asako. 2021. "The effectiveness of mobility control, shortening of restaurants' opening hours, and working from home on control of COVID-19 spread in Japan" Health & Place 70: 102622.
・Chiba, Asako. 2021. "Modeling the effects of contact-tracing apps on the spread of the coronavirus disease: Mechanisms, conditions, and efficiency" PLoS ONE 16(9): e0256151.

・Reference: Kerr et al. (2020)

・At Day 0, the daily number of new positives in Tokyo is about 800 people
・Infectivity of the δ variant (estimated as "infectivity that reproduces the actual number of infected people in a simulation that reflects the most recent human flow and vaccination status")

・Tests
30% of symptomatic patients are tested (test sensitivity 70%)
・Restrictions on outings
Assuming that only the number of unvaccinated people going out decreased by 30% compared to the normal level, and that those who have fully vaccinated will return to normal activities (vaccine pass, etc.)

・Vaccination
Considering the infection-prevention effect against δ variant and the decline of the effect 6 months after vaccination

・Infection-prevention effect against Delta variant
　→　Sensitivity: 85%, Serious illness rate: 50% (at the completion of the 2nd vaccination, compared to unvaccinated)

・The decline of the infection-prevention effect
・6 months after the 2nd vaccination, sensitivity decreased to 60% (compared to unvaccinated)
・Vaccination status at the time of lifting (early October)

(Based on data released by Cabinet Public Relations Office. The number of people vaccinated in September is estimated based on actual results during the month.)

・Antibody cocktail administration is assumed to be 70% effective in preventing moderate illness
・The following hypothetical scenario was compared with the basic scenario of a "total of 20,000 doses*1 being administered to positive patients on the day after the confirmation of results".

・Administration is limited to "positive patients who have underlying diseases."*2
・Total number of doses is 10 times of the baseline
・Total number of doses is 20 times of the baseline

*1: Estimated for Tokyo based on the fact that 200,000 doses are secured nationwide.
*2: Modeling of "persons who have underlying diseases"
Assumed that 35% of the elderly (65 years and older) have underlying diseases (see p. 8)
The "probability that a person who have underlying diseases will develop mild to moderate illness" is 2.5 times higher than those who does not have such underlying diseases (see p. 9). *3
*3: In this model, the following transitions are assumed: mild - moderate - severe - death. There are a myriad of possibilities as to which stage the probability increases, but this simulation assumes "The rate of mild to moderate disease was 2.5 times higher, and the rest was independent of underlying disease.“ Under this assumption, the maximal reduction in bed strain (number of patients with moderate or severe symptoms) is theoretically achieved when the antibody cocktail is administered only to those with underlying disease.

(Compiled from the Ministry of Health, Labour and Welfare, Patient Survey 2017.)

Case of mortality rate

(Created based on "Age-Specific Case of Mortality Rates in COVID-19 Infections Using COVID-19 Registry Data" from National Institute of Infectious Diseases (2021).)

The mortality rate indicates the probability of death for those with the disease and is expressed as the number of deaths/number of diagnosed cases.

・Given the current supply (equivalent to a total of 200,000 doses), the administration of antibody cocktails will reduce the number of deaths by several hundred in 4 months during the course of the outbreak
・If the treatment is limited to patients with underlying diseases with a high rate of severe disease, the number of deaths will further decrease by several hundred
・Delayed growth in the number of patients with moderate or severe disease (greatly slowing bed strain) is not significant