It’s happening again: COVID-19 cases are back on the rise. There are 3 main reasons why 

COVID-19 infections continue to rise, driven by new and more infectious omicron subvariants, waning immunity from both vaccines and previous infections and fewer people masking up, health officials said at a White House briefing Wednesday.

https://www.usatoday.com/story/news/health/2022/05/18/omicron-waning-immunity-rising-covid-cases/9823740002/