Originally posted by Larrymc Robert, that might be a bit short for the Pfizer vaccine. According to the Pfizer hand out the shortest time period between shots for the Pfizer is 21 days not two weeks. Moderna is 28 days. I've read that a slightly longer period between shots is somewhat more effective than shorter periods of time.
Again according to the Pfizer hand out "The second dose should be administered as close to the recommended interval as possible. The vaccine can be given up to four days in advance of the recommended interval if a patient presents early and you are concerned they will not return at the appropriate interval for vaccination. However, there is no maximum interval between the first dose and second dose for either vaccine, The series does not need to be restarted".
The data out of Israel seems to indicate that Pfizer's vaccine is 75 percent effective two weeks after the first dose.
DEFINE_ME I assume Moderna's vaccine is probably similar, but I don't think there is data on that. It probably makes sense if vaccine is in short supply to space out the first and second shots to try to get more people immunized. Eventually you do need to give the booster or that immunity will wane, but as you say, you never restart the series even if you would go five or six months between shots.
I do think the reason that Pfizer and Moderna went with such a short space between their vaccine doses in the trials was not because they thought that was ideal, but because they wanted to complete the trials ASAP. It worked, but probably spacing them out a bit isn't harmful and might lead to fewer side effects from the second dose.
(The CDC is very conservative and will only recommend what was tested in the trials so we'll be going with that for now in the US).