A lot of countries in South America had very strict rules. Double-mask requirements, mandatory vaccines, stay-at-home days. What they perhaps lacked in access to vaccines, they tried to make up with those stricter rules. They also made deals with China & Russia for their vaccines, in lieu of limited access to Pfizer etc.

A better term would be “developing nations” . The term " third world" refers to not being part of NATO (or not aligned to NATO), and is outdated. Also, there are various sorts of developing countries, richer, poorer, and some are war or conflict zones.

Each one in a different way.