Impact of active domestic travels

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

Effect of Antibody Cocktail
・Taking into consideration the limited supply, administration only to those with underlying medical conditions will help reduce the number of deaths
・The number of deaths would decrease further if supply of antibody cocktail increases
・Even if the supply increases, the effect of easing the tightness of hospital beds may be limited

※1 Normal level refers to the level before the COVID-19 pandemic.
The number of people going out of -30% of normal is equivalent to the level as of mid-September 2021.

< Overview >
・Growing debate on the resumption of “GoTo Travel”
・Analysis of the impact on infections of an increase in domestic long-distance travel compared to the current level

< Results >
・Even if domestic travel recovers to normal levels, the number of infected people will only increase by 10-20% of the current level if the number of people going out each day is maintained at the current level
・On the other hand, even if domestic travel is maintained at the current level, an increase in the number of people going out routinely of 5 percentage points above normal will spread infections to the level same as when only domestic travel were to recover

< Implication >
・If the number of people routinely going out can be controlled, the impact of increased long-distance travel will be minor
・However, if the increase in eating and drinking opportunities associated with increased travel is taken into account, there is a risk that this could lead to the spread of infections
・The use of vaccine passports (not assumed in this study) is expected to further reduce the effect of the spread of infections

・Domestic model based on “Relaxing behavioral restrictions following the spread of vaccination” (released as COVID-19 AI & Simulation Project on August 24)
・Considers communities between each prefecture and the movement of people between 8 major metropolitan areas
・Individual attributes: age, gender, industry, occupation, frequency of eating out, history of underlying diseases
・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)

・Models the movement of people between 8 major metropolitan areas, taking into account regional characteristics
・People from different metropolitan areas do not usually come into contact with each other, but they may come into contact with each other when they travel or go on business trips and move between metropolitan areas

・Assuming infectivity at the same pace of spread as in the early fifth wave

・Tests
30% of symptomatic patients are tested (test sensitivity 70%)

・Vaccination
Considering the effect of preventing Delta variant infection
Assuming booster vaccination 6 months after 2nd vaccination, and the decline of the effect is not considered

・Restrictions on outings
Uniformly -20% compared to the normal level (based on the most recent human flow data for downtown areas)

・Travel
Uniformly -50% compared to the normal level (based on the most recent overnight travel statistics survey)

Does the activation of domestic travel lead to the spread of infections?

< Results >
Even if domestic travel recovers to normal levels, the number of infected people will only increase by 10-20% of the current level if the number of people going out each day is maintained at the current level
On the other hand, even if domestic travel is maintained at the current level, an increase in the number of people going out routinely of 5 percentage points above normal will spread infections to the level same as when only domestic travel were to recover

< Implication >
If the number of people going out routinely can be controlled, the impact of increased long-distance travel will be minor
However, if the increase in eating and drinking opportunities associated with increased travel is taken into account, there is a risk that this could lead to the spread of infections
The use of vaccine passports (not assumed in this study) is expected to further reduce the effect of the spread of infections