One that I am aware of. For those who get one, you get it at the start of flu season, once a year.
For the purposes of today's political climate, it is completely voluntary, and nobody gives a crap whether you get one of not. Except the US Navy. The US Navy makes sure that no matter where you are (trying to hide), all Marines and Sailors get theirs
“When bad men combine, the good must associate; else they will fall, one by one, an unpitied sacrifice in a contemptible struggle.” Edumnd Burke
“You know the world is going crazy when the best rapper is a white guy, the best golfer is a black guy, the tallest guy in the NBA is Chinese, the Swiss hold the America's Cup, France is accusing the U.S. of arrogance, Germany doesn't want to go to war, and the three most powerful men in America are named "Bush", "Dick", and "Colin." Need I say more?” - Chris Rock
I don't think any vaccine can manipulate itself so it's not really different in that respect. But "they," the sciencey people, can manipulate the mRNA vaccine more quickly than they would be able to do with a traditional vaccine. From what I understand the vaccine has been surprisingly resilient against the new variants but I'd imagine that there's a limit to how far it could go.
A new one every year but they create it based on what is happening in South America??? and a prediction on what the flu will actually be in any given year. Apparently the new flu virus comes from a combination of the flu floating around in pig, bird, and people populations and can combine very easily in different permutations. The advantage with covid is that we have the actual gene sequencing to work with from which to design the vaccine. Not so much with the yearly flu variants. That's what a virologist friend of mine who happens to work at the CDC was trying to explain so discount whatever I just typed based on my memory from 3 weeks ago.
"when socialism fails, blame capitalism and demand more socialism." - A friend
"You know the difference between libs and right-wingers? Libs STFU when evidence refutes their false beliefs." - Another friend
“Don't waste your time with explanations: people only hear what they want to hear.” - Paulo Coelho