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Early on in the pandemic, there were high hopes that a vaccine would eventually allow society to return to normal.

But according to a recent study submitted to the central government, people may need to adjust their expectations on what “normal” looks like due to the spread of the highly contagious delta variant.

If people return to their pre-pandemic lives and don’t take proper precautions, 100,000 people in Japan could die from COVID-19 over the course of a year even if a 90% vaccination rate is reached, according to the study by a Kyoto University researcher.

Yuki Furuse, an associate professor of infectious diseases, conducted a simulation that looked at expected death tolls based on different scenarios for the vaccine rollout and lifestyle changes.

The simulation assumed a mortality rate for unvaccinated persons of 5.7% for people in their 60s or higher, 0.2% for those in their 40s to 50s, 0.01% for those in their 20s to 30s and 0.005% for teens and under. The vaccine’s efficacy for the delta variant was presumed to be 70% against infection and 90% against hospitalization, serious symptoms and deaths.

Even if 90% of residents get the shot, annual deaths of 100,000 or more in the country can be expected if social distancing and mask-wearing measures are no longer in place. The study assumed a reproduction number of 5 for the delta variant, meaning on average each infected individual would infect five others.

But if the vaccination rate reaches the target levels of 90% for people in their 60s and older, 80% for those in their 40s and 50s and 75% for those in their 20s and 30s, and people reduce unsafe interactions with others by 40% through masking and avoiding closed spaces, crowded areas and close-contact settings, the number of deaths could fall to around 10,000 annually, on par with annual deaths from the flu.

If the vaccination rate was a bit lower than those targets, at 80% to 85% for people in their 60s and over, 60% to 70% for those in their 40s and 50s and 45% to 60% for those in their 20s and 30s, a 50% to 60% reduction in contact with others would be required to keep the death toll at around 10,000.

So far, as of Friday 61.9% of residents had received at least one shot, with 49.8% having been fully vaccinated, according to a survey issued by the Cabinet Secretariat.

Japan has so far had more than 16,700 deaths since the pandemic began early last year, but about half of those deaths have come in the last six months due to the spread of the delta variant.

“Depending on the spread of infections and tightness of medical services, the chances are high that we will continue to see a society that would repeatedly set up and cancel strong measures such as quasi-emergency measures or states of emergency,” Furuse said in the study.

A staffer checks the temperature of a woman at a vaccination center in Nagoya on Saturday. | KYODO
A staffer checks the temperature of a woman at a vaccination center in Nagoya on Saturday. | KYODO

The government’s subcommittee on the coronavirus response, which received the study under advisement, on Sept. 3 compiled recommendations that curbs on social activities would need to be kept in place in tandem with a gradual relaxation in movement restrictions, adding that vaccination alone cannot be grounds for lifting restrictions on social lives entirely.

In line with findings abroad, the research prompted the subcommittee headed by Shigeru Omi, the government’s top COVID-19 adviser, to acknowledge for the first time the limitations of the vaccine in the fight against the pandemic, citing the possibility of breakthrough infections in fully vaccinated people and a gradual decline in vaccine-acquired immunity over time, among other reasons.

“Based on those reasons and insight from overseas, even if all the willing individuals finished the vaccination, the acquisition of herd immunity to protect the society as a whole is considered difficult,” the subcommittee said in a statement.

Furuse’s study also showed the outlook would be far different if the delta variant was only as contagious as the alpha variant, which once made up the majority of cases in Japan before it was swept aside by the delta variant. The alpha variant is considered to be up to 50% more transmissible than the original strain of the coronavirus.

Assuming a reproduction number of 3.5 for the alpha variant and the vaccines’ efficacy of 90% against infection and 95% against severe disease or death, cumulative deaths would have been much lower than 10,000 annually despite a reduction in human-to-human contact that is lower than 40%, the study showed.

If the infectiousness of the delta and other new variants that could emerge from now on were to have a reproduction number of around 7.5, there’s a high possibility that strong restrictive measures would be required in the future even if the vaccination rate reaches 90%, Furuse added.

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