Not long enough to require a third or fourth booster per Israel and some other countries, so not a good analogy unless we're all bad COVID students.

To the best of my knowledge the first COVID vaccine dose immune response is not short-term, except in the sense that it is weaker and therefore will fade below an effective level in a smaller amount of time. But it fades at the same rate as the second dose. The second dose just "raises" the response level higher than the first dose got it.