Two vaccines, Pfizer must be kept cold, Moderna doesn't. You need two shots within 10 days, then come back in six months.
The pfizer dose is one shot now then another 21 days later.
The moderna dose is one shot now then another 28 days later.
The Johnson & Johnson vaccine is set to be available in March (at least in the USA) and will be a one dose shot.
There is a slowdown is delivery of pfizer vaccine due to an international shortage. I figure I may have to wait until sept to get the first dose.
Eventually vaccine will mature & become something like flu shot.
This might be the case.