We have seen what happened in Manaus. The city had 76% of its population infected, which was more than enough to achieve herd immunity via infection to the original strain. The natural herd immunity mechanism COVID-19 does not allow a person to be protected from more than one strain a time post infection for more than 6 months, and this the natural herd immunity Manaus experienced was broken by a new variant. As long as the number of cases in a region overshoots the herd immunity threshold, new variants are created, and this may result in the reverse of herd immunity. This will continue repeatedtly until a strain is produced that kills all of the infected propulation, and only then will herd immunity through natural infection be achieved. Natural herd immunity can only work for a short period of time due to population turnover, and it is limited to viruses with obligate viremic spread, of which COVID-19 does not meet this criteria.