Checking in from Sydney here, summer is still a month away, my family is snuggled on the lounge under blankets right now.

The result comes down to a competent government response to a public health crisis. Not the weather.

Here in New Zealand the virus was eradicated in the winter, then again in the late winter/spring. Did the US and UK control it in their summers?

NZ completely closed the borders. That's a huge factor.

Returning residents bring in covid - they have been allowed back at all stages. Some days there is none, but on most days several cases come into the country. Essential workers are also allowed in, although this has become a political football. For example, a equestrian race track builder was allowed in.

We are not in summer yet (i.e., I do not see any bushfires outside my window) but the weather is starting to warm up a bit (many low to mid-20C days) here in Melbourne. I'm not convinced weather is the only factor.

I'll check back here in 12 months when Americas cases never stop rising

We've been in winter since June. We're only just into spring here, so no, summer hasn't helped (yet).