Solar UV radiation may greatly reduce the risk of transmission through contaminated surfaces, but it doesn't help much in a densely packed society with Third World sanitation standards and a lot of close physical contact.
I would expect warmer weather and intense sunlight will help keep the spread down in places like the Southern US or Singapore, perhaps, but not in some of these other countries.
Some info on temperature and COVID-19:
“Temperature significant change COVID-19 Transmission in 429 cities”
- see https://www.medrxiv.org/content/10.1101/2020.02.22.20025791v1
“Temperature and Latitude Analysis to Predict Potential Spread and Seasonality for COVID-19”
- see https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3550308
“Seasonality of SARS-CoV-2: Will COVID-19 go away on its own in warmer weather?”
- https://ccdd.hsph.harvard.edu/will-covid-19-go-away-on-its-own-in-warmer-weather/ (not peer-reviewed or submitted for peer review, so read with the appropriate caution)
There’s nothing definitive, yet.