Why do you think "northern hemisphere summer" would have any (positive) impact? I mean, just look at Brazil, an "eternal summer" country, they're not doing that well... Except if it's the combination of heat+low humidity, there might be counterexamples to that as well though (Iran?).
It's a guess, but a plausible one. We know the virus is destroyed quickly by UV light, which is stronger in summer. People spend more time outside in summer, and we know transmission is reduced outside. Other respiratory viruses spread poorly in summer.
It's hard to compare with Brazil, because the stats coming out of there are poor and they're making less attempt at controlling the virus compared to almost any other country.
It's not the heat but the UV exposure and people's ability to create vitamin D from it. People in countries that have "eternal summer" tend not to go out in the sun as it's hot. Also skin pigmentation is a big factor.
Is that really true? Most of these "hot" LATAM and asian countries do not have wide-spread central air conditioning. In those countries, staying inside is horrible in the hot months.
