no rule as such. no person can force you to inject/ take medicine anywhere in the world. But will manipulate you in someway to get it.no country can restrict you from entering anywhere. If so there has to be a workaround for those people as well. Vaccinated people are more dangerous beings than those who have not for me. Atleast they try to protect them selves and try to protect others while those who took the vaccine carry more mutations giving less care for others protection and spread the virus all over