[CryptoPunk]

It doesn't reduce it enough to provide herd immunity, meaning the virus will continue to propagate until every one has been exposed. See Iceland's experience:

https://twitter.com/eliaseythorsson/status/14240115421950238...

The Oxford Vaccine Group says herd immunity through vaccination is infeasible now:

https://www.theguardian.com/world/2021/aug/10/delta-variant-...