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Recent COVID-19 cases in Japan have shot up sharply, leading to another round of partial lockdowns, but reported cases appear subdued compared to the United States or Europe.

Total cases in the United States have surpassed 23,000,000 cumulative while the cumulative number for Japan passed 315,000 cases. That is 69 cases per 1,000 people in the United States compared with two cases per 1,000 in Japan. If Japan had the same ratio of cases per 1,000 people as the United States, Japan would have more than 8,700,000 cases. That approximates the population of metropolitan Tokyo.

If the United States had the same ratio of cases per 1,000 people as Japan, the number of cases would be under 660,000. That is about the population of Oklahoma City. Much has been researched and written about this disparity, but we will probably not learn of meaningful factors that can explain it for several more years.

Behavior and surges

The lower case numbers in Japan may allow us to tease out a rough correlation between human activity and case surges, the kind of correlations that have been obliterated in the United States by the enormous scale of its pandemic.

Consider the following chart showing the R or the effective reproduction rate that estimates how many new patients each known carrier likely infected in Japan.

In March, with quarantine standards still loose, the R spikes as hospitals try to cope with this unfamiliar virus and in-hospital infections soar. On April 7, a partial nationwide lockdown is declared and the R is pushed down below 1.0, meaning the number of new infections per known virus carrier is declining.

The authorities become optimistic with the reduced R and the partial lockdown is lifted on June 19. People begin to move around and congregate as if to celebrate a victory over the virus. But two and a half weeks later on July 6, we get a spike in the R value to 1.8. The average known carrier at this point is infecting almost two other people during his infectious days.

Beware the long weekends

That’s the first of several incidents of a period of heightened movement and congregation of people; followed roughly two weeks later by a spike in the R as it takes the virus roughly two weeks to induce symptoms.

The next spike shown comes on Aug. 3 or eight days after the four-day weekend from July 23 to July 25. The four day weekend of Sept. 19 to 22 is followed 10 days later by another spike in the R on Oct. 2. The Nov. 13 spike is preceded 10 days earlier by what is known in Japan as a tobi-ishi renkyu or a four day weekend (if you also took Monday off) between Oct. 31 and Nov. 3. And now it looks like we are experiencing the spike of Jan. 11, which follows the year-end and new year holidays by a little over a week. Jan. 11, a Monday, was itself part of a long weekend, so we may have another spike coming soon.

The 2021 Japanese calendar shows two long weekends in February. (The holidays are on Tuesday and Thursday but many employees will take the respective Monday and Friday as leave so they have four days off each time.) But there are no long weekends in March.

All of this suggests that authorities would do well to keep the current lockdown in place through February instead of ending it on Feb. 7 as planned.

Another policy implication may be for authorities to shut down restaurants and bars from the eve of a long weekend and allow regular hours after the weekend is over — and compensate restaurateurs for only the closed days instead of providing a sweeping, rolling payout.

Hidden virus carriers

It has been known since the early days of this pandemic that some people infected with the SARS-Cov-2 virus that triggers the COVID-19 sickness show absolutely no symptoms. These asymptomatic carriers tend to be young — in their 20s and 30s with strong immune systems. Many are unaware that they have the bug.

Importantly, these “hidden carriers” of COVID-19 can unknowingly infect others. Indeed, they may be the main vector of the disease. As long as we have these hidden carriers moving about and congregating — especially during long weekends — COVID-19 will remain a part of our lives.

There is much discussion about how the vaccines will change — or not change — this picture. Some epidemiologists think the virus will be among us forever just like the influenza virus. This is a complex discussion best left to the licensed, certified and experienced.

How many hidden carriers?

But we can review the emerging consensus among the scientific community, which is that the number of bug-spreading asymptomatic carriers is likely smaller than initially estimated. Early literature on this topic ranged from 5% to 80% of those exposed to the virus — the wide variation owing to the fact the researchers were reporting from given samplings. The Diamond Princess sampling yielded 18%. The U.S. Center for Disease Control was assuming 40% until late last summer.

Given the larger quantity of data available globally now, the consensus estimate has moved lower, to 20%. This is good news. This is closer to the 14% rate for asymptomatic carriers of the influenza virus, another single strand RNA virus, with which we have been sharing this planet for centuries.

Behavior should follow science. When the asymptomatic carrier estimate was 40%, I was holding my breath and hence red-faced when crossing paths with other people in the streets of Tokyo. Now that the estimate is 20%, I am holding my breath less. I now choose to sit next to elderly subway passengers and keep my distance from sprightly youths. My barber is in his 80s, almost retired and appears to have few customers. Perfect!

Matt Aizawa is a former Japan Times journalist who was also a longtime Tokyo-based securities analyst. This article was first published by Asia Times.

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