Just as variants are expected with any virus, so are vaccine breakthrough infections. These breakthroughs can happen for several reasons. A variant, immunocompromised or immunosuppressed individuals, vaccines aren't 100% effective (remember NOTHING is), some people's bodies don't accept vaccines (this is called immunocompetent), and it can just happen without scientific explanation. Regardless of the reason, breakthrough infections are rare but expected.
A study in Washington state gathered data from over 4 million fully vaccinated people. The data showed a rate of about 1 in 5,000 experienced a breakthrough infection between January 17 and August 21, 2021. More recently, some populations have shown breakthrough infection rates of approximately 1 in 100 fully vaccinated people.
So, if someone is going to get a virus that can be addressed with a vaccine (which, of course, nobody knows if they are going to get it or not) then why bother getting the vaccine? Breakthrough coronavirus infections can cause mild or moderate illness, but the chances of serious COVID-19 are very low, especially for people who are not living with a chronic health condition. The COVID-19 vaccines are very effective in keeping you from having to go to the hospital, being put on a ventilator, or dying due to severe coronavirus disease.
Critics and skeptics might point to the recent death of former U.S. Secretary of State Colin Powell to refute the low occurrence of breakthrough infections in fully vaccinated people. However, Powell was immunocompromised due to battling multiple myeloma as well as Parkinson's, leaving him susceptible to complications. All along scientists and the medical community have made it clear that those who are immunocompromised or immunosuppressed are at greater risk from the virus, but that vaccination does provide a level of protection and is recommended.
Sources: hopkinsmedicine.org, cdc.gov
