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.
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.