Many vaccines, e.g., polio and smallpox back in the day tend to be one or two and done.
If it’s a truly effective vaccine, then it doesn’t have to be repeated forever.
The reason there is an annual flu shot, and maybe an annual covid shot, is that those viruses keeps mutating well within the span of a twelve month period, so you have to keep updating the vaccines to keep up with the viral mutations in the strains in active circulation.
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