While I am enthusiastically pro-vaccine (and in fact got both versions of the shingles vaccine) I have to point out that some people do have a lasting effect from the immune system's response and memory. This first became publicized after the population-wide swine flu vaccination program in 1976. The program was officially halted on December 16, 1976, after the vaccine was linked to an increased risk of Guillain-Barré syndrome, a rare neurological disorder. I remember this well because I and my entire family got this vaccine. We were hit hard by the 1968 Hong Kong flu.

Very true - and I wasn't implying vaccines can't have side effects. I was just pointing out that any harm caused by a vaccine must originate shortly after vaccination, because that's the only time the body is actually exposed to it.

There are many who falsely believe that a vaccine lingers in the body and can spontaneously produce harmful effects later in life, but there's no plausible biological mechanism for that.

That's why vaccine safety monitoring focuses heavily on the weeks and months after vaccination. When genuine vaccine-related adverse events occur, they are overwhelmingly detected within that timeframe.

As for Guillain-Barré syndrome, my father was actually one of the people to develop that, but in his case it was a result of an infection rather than the swine flu vaccine.

That's another important point people often overlook: the same immune response that can (rarely) be triggered by a vaccine can also be triggered by the disease itself, often at a much higher rate.

So even when a vaccine carries a real risk of side effects, it can still be a net positive if that risk is substantially lower than the risk posed by the disease it helps prevent.

Myocarditis is a prime example of this. While it can occur rarely after COVID vaccination, the risk of it occurring is far higher from the COVID infection itself.