I don't have any thoughts on Thailand's hot climate other than it'd be a nice place for a vacation.
https://www.asiaone.com/asia/no-new-covid-19-cases-thailand-over-24-hour-period
A lot has been written recently about Vietnam (also on the Indochinese peninsula and also bordering China) and the few cases and fewer deaths. For example:
How Did Vietnam Become Biggest Nation Without Coronavirus Deaths?
For a deeper dive, here is a lengthy explanation that you are free to discount if you think Bill-Gates-is-the-boogeyman:
Emerging COVID-19 success story: Vietnam’s commitment to containment
June 30, 2020
Introduction
Although Vietnam reported its first case of COVID-19 on January 23, 2020, it reported only a little more than 300 cases and zero deaths over the following four months.
1,
2 This early success has been attributed to several key factors, including a well-developed public health system, a strong central government, and a proactive containment strategy based on comprehensive testing, tracing, and quarantining. Lessons from Vietnam’s successful early detection and containment strategy are worth examining in detail so other countries may apply them to their own responses.
Detection: Vietnam has taken a targeted approach to testing, scaled up testing in areas with community transmission, and conducted three degrees of contact tracing for each positive case.
Containment: As a result of its detection process, hundreds of thousands of people, including international travelers and those who had close contact with people who tested positive, were placed in quarantine centers run by the government, which greatly reduced transmission at both the household and community levels. Hot spots with demonstrated community transmission were locked down immediately, and the government communicated frequently with citizens to keep them informed and involved in the public health response.
One of the reasons Vietnam was able to act so quickly is that the country experienced SARS in 2003 and human cases of avian influenza between 2004 and 2010. Therefore, Vietnam had both the experience and infrastructure to take appropriate action. As the COVID-19 pandemic continues to unfold and Vietnam relaxes many of its restrictions, monitoring how the case levels change, and studying the reasons for those changes, will be particularly important.
Source:
Emerging COVID-19 success story: Vietnam’s commitment to containment