The problem with T cell immunity is it isn’t really any immunity - it’s just a “building block for your immune system to be able to formulate a response” - meaning once the virus gets a hold of you and you’re sick, your immune system doesn’t have to start from ground zero to figure out how to respond, it has a blueprint to start constructing the immune response (unlike the first 120 days after you get the shot, you’ve actually got an active immune response still going on with the ability to respond instantly and generally may entirely prevent illness) - so it means you’ll still get pretty sick with a T cell only response, you just shouldn’t fall victim to a cytokine storm caused by a confused immunity with an inability to cope with fast spreading virus.
Unfortunately now there’s also measles back in circulation due to low uptake of MMR shots - and measles is amazing at entirely deleting all of your existing T cells - meaning all those memories your immune system had blueprints for go away and are replaced entirely with “ONLY MEASLES!” T cells - so you’ll have an amazing ability to not get that again, for a decade or more, but you’ll have nothing to help with covid, flu, other coronaviruses, rhinoviruses, RSV, and various other viral infections (some recent research by virologists says a bad case of measles will even erase your tetanus and pertussis and other immunities you may have had from other vaccinations). That’s not going to help.
