A handful of countries have not reported any covid positive cases. These are small countries with very low population and fewer visits by foreigners. So probability of an infected individual landing in these countries are less.
According to available information on some websites, only 12 countries have not confirmed any cases of COVID -19. North Korea, Turkmenistan, Solomon Island, Vanuatu, Samoa, Kiribati, Federated States of Micronesia , Tonga , Marshall Islands , Palau, Tuvalu, and Nauru.