Actually, swine flu never went away, it's still in circulation, although it's covered by seasonal flu vaccines.
Interestingly, it turns out flu vaccines are accepted as about 60% effective - not sure if that means they are only effective against a percentage of the strains expected to be in circulation each winter (so 40% of flu strains might not be covered), or if it also means you can still catch a flu strain you've had the jab for but are less likely to be severely affected. That got my interest going because I had the swine flu jab, but was absolutely floored by flu later that year, at a time when several work colleagues, and Paul, went down with what was suspected to be swine flu. The cough was really bad, but luckily it all cleared up after about a week and a half.
There's a suggestion that it's still possible to contract Covid-19 after having the Oxford Coronavirus jab - the monkeys did - but that it's a lot less severe.