[newsyyswen]

There are no conclusive numbers on how long they last, because there has not been a significant drop-off in efficacy yet.

There is some evidence that booster shots after 6 months can provide better even better protection than the second shot after 3-4 weeks, but it's not clear whether they will be necessary yet, especially when so much of the world is still desperate to get the first two shots in peoples' arms.

[AndrewBissell]

There's been enough drop-off in the Pfizer vaccine that Israel is starting boosters for people 60+. Their estimate is that protection against mild disease has dropped to 40% and protection against hospitalization to 88%. https://swprs.org/covid-vaccines-the-good-the-bad-the-ugly/

[dtech]

There has been shown a little bit of drop-off, but that is in the range of 95% to 80-90%, so still strong. Hard to say because the mutation in circulation have changed.