Covid-19 numbers in Japan and Germany this autumn

My home state of Bavaria (population: 13.1 million) in Germany has had 30,117 new Covid-19 cases in the past 7 days, a 7-day incidence rate of 229 per 100,000. Meanwhile, Tokyo (population: 14.0 million) has had 142, a 7-day incidence rate of 1 per 100,000. The difference in numbers is simply staggering. Given that Germany started vaccinating its citizens months before Japan, it had a headstart on the road to immunity but it has since given up this advantage. A larger share of Japanese residents is fully vaccinated in every age group than in Germany. The growth in the vaccination rate slowed to a crawl in Germany months ago, while it’s still continuing at a healthy clip in Japan.

About two months ago, Tokyo’s Covid incidence (147 per 100,000 in 7 days on 2021-09-03) was quite similar to Bavaria’s current rate. But while the Covid incidence rate has been falling week after week in Japan since early September, it has almost doubled in Germany. The Japanese drop in cases has been amazingly consistent. When cases fall by half every 8 days and this continues for 8 weeks then cases will fall over 100-fold overall. That’s what an exponential decrease looks like. It happens when the reproduction rate of the virus drops below 1.

According to a numerical model created by Kris Popendorf, the two main contributors to the swings in the reproduction rate of the virus are mobility and immunity (you can read more details about his model here). One pushes the number up, the other pushes it down. The combined changes of the two either push the number above 1 (case numbers grow) or below 1 (cases drop). There are other factors, such as adherence to mask-wearing in indoor situations but in Japan’s case this has barely budged even when cases have been falling. Even when the risk of encountering infected individuals has decreased, few Japanese have stopped wearing masks as they still strive to comply with social norms.

With the end of the state of emergency, mobility has increased. People have started to go out and travel again and companies are reducing remote work. On the other hand, while rates of immunity will increase further, this increase is slowing down as the vaccination campaign will be nearing the saturation point over the next month or so. This will shift the balance of the two factors driving the reproduction rate of the virus towards the factor that drives an increase. We can therefore expect the rate of drop to slow and eventually rebound when mobility reaches a level that outweighs the level of immunity in the population. To achieve herd immunity regardless of mobility, the vaccination rate would have to reach a level estimated to be as high as 85-90 percent, which even Japan is unlikely to reach.

Case numbers in Tokyo are now at a level about 1/200 of the peak in August. Therefore even when the numbers start rebounding and grow again, there remains some time for public messaging to prevent a return to a caseload that would overwhelm the healthcare system.

I am much more concerned about the situation in Germany, which has a significant population of people reluctant to protect themselves and others by getting vaccinated. While not as large as in Russia, Romania, Bulgaria or the USA, it makes it very difficult to get numbers under control. In Bavaria, the Covid-19 incidence amongst unvaccinated people is 9 times higher than amongst fully vaccinated people (451.5 vs. 50.9). This means that even though about 65 percent of the population are fully vaccinated, the vast majority of cases are of unvaccinated people. Only 39 percent of teenagers are fully vaccinated there while more than two thirds of teenagers in Tokyo will soon have both shots. Even for age 65+ the rate is 80 percent in Bavaria vs. 91 percent in Tokyo, which means there are proportionally more than twice as many unvaccinated seniors in Bavaria as in Japan.

Unfortunately it will be very difficult to change the attitudes behind the vaccine resistance in Germany and other countries, as it is an issue of trust. Many of the people reluctant to get the shots trust neither politicians nor mass media nor medical professionals nor science in general. They will therefore be difficult to reach.

Restrictions on public activities, such as eating out or travel that are becoming more convenient again for low-risk vaccinated people will gradually erode the non-vaccinated population share but that will take time.

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