It's possible that due to the heat, many people stayed in air-conditioned rooms without ventilation, and that this played a part in the increase in infections.

What is an air conditioner but a form of ventilation?

Is everyone waiting for the coronavirus to reach zero? Not going to happen. Neither is influenza nor the common cold. Isn't it time to ditch the masks and magic plastic curtaining? I think so.

a specially appointed professor at Tokyo Medical University

Must be how they were able to come up with such an insightful observation!

What is an air conditioner but a form of ventilation?

Not the form that would be helpful at preventing the dissemination of viral respiratory infections, cooling down or dehumidifying the same volume of air would not count as ventilation in the same way as replacing that air with fresh one from outside for example.

We open all windows every day to refresh the air.

Influenza being labeled COVID19 could have something to do with it.

Is everyone waiting for the coronavirus to reach zero?

Variants of SARSCoV2 will stick around, but Covid19 (the illness) is rapidly becoming irrelevant.

Maybe it is because people have stopped wearing masks, the latest wave coincides with a general relaxation of preventive measures.

What is an air conditioner but a form of ventilation?

Of course, it depends on what kind of air con you use. For efficiency reasons, most air cons do not ventilate the air. Though, there are exceptions...

The question is, what kind of air cons do they use in the trains? Have they been "ventilating" the trains for three years with closed systems?

Second, let's not forget that air cons are filtering the air. These filters should be treated just as COVID masks. During these three years, did anyone hear anything mentioned on how to replace/clean the air con filters to prevent infection spread?

In many respects, we are still living in the dark ages...

The weather has been pleasant. Only turned on the air con in one bedroom three times this summer. My place is breezy.

We open all windows every day to refresh the air.

Smart after passing all that gas.

What is an air conditioner but a form of ventilation?

Air cons "condition" air, that is, heating or cooling it. This is done by circulating the air in the room. Ventilation is expelling room air and replacing it with fresh air from outside.

You can buy ventilating air cons but they are top of the line and you cannot get kanreichi (cold zone) ones. You can also buy ventilators that heat or cool outside air by passing it next to the room air they are expelling. This can be done via a system of built in ducts, probably the best way or can be done with a small wall mounted thing. One brand is called "Rosunai" (no loss).

Why would infections "abate"? You can recatch coronavirus because getting it does not make you immune. I thought the idea was now "coexistence", and for most folks to not worry about it.

Nonsense. What does ac have to do with the transmission of a virus? Is a sick person standing on the other side, breathing into the machine?

Ridiculous.

What’s causing the increased transmission is the insistence of people, like the commenter above me, of trying to go bAcK to nOrmAl and be outside, coughing and sneezing with no mask on.

The weather has been pleasant. Only turned on the air con in one bedroom three times this summer. My place is breezy.

What?! Where do you live, Antarctica?