In decades past people volunteered for the annual influenza vaccine. Inevitably a year later, a variant strain or new flu would appear requiring another shot for those volunteers.
Usually a flu shot in September-October would protect, for the most part. Some years, a different strain would surface in January, enforcing the need for a shot.
Speculation may not be so far-fetched. One outcome of the Covid 19, Coronavirus may be in setting a mandatory worldwide mindset for annual inoculation…..