A: No. There is really no reason to think that protection from the vaccines wears off after 90 days.
We know the vaccines last longer than 90 days. But we don’t know how long.
The CDC recently updated their guidance about quarantining after an exposure and included some changes for people who have been vaccinated. They said that if you have a known exposure to someone who has COVID-19 and you completed your vaccination series at least 2 weeks ago *but less than 90 days ago*, you do not need to quarantine.
This update probably raises more questions than it answers. First, does that mean that a fully vaccinated person cannot get a mild/asymptomatic infection and pass it on to other people? And second, holy cats does this mean the vaccine “wears off” after 90 days?!?!
The answer to the first question, about whether the vaccines completely prevent infection or just serious illness, is largely unknown right now. But as the Magic 8-Ball says, signs point to yes–the vaccines likely do reduce the chances of asymptomatic transmission. We await more solid information here. (see recent post)
As for whether the vaccines provide immunity for just 90 days?
There is NO indication that the vaccines quit working after 3 months, at all. Some of the people in the Pfizer and Moderna Phase 2 studies have been fully vaccinated for over 7 months at this point, and there is nothing suggesting that their immunity is weakening so far. We do not know exactly how long immunity from the vaccines lasts right now… it might be 1 year, 5 years, 10 years.
We DO know that it is more than 90 days.
We do not have any special insight into the internal workings of CDC, but from what we can guess, the purpose of this update was to make the guidance for vaccinated people sync with the recommendations for people who have recently recovered from COVID-19. It seems to us like in the absence of information, CDC just picked 90 days as an arbitrary benchmark and wanted to make the recommendation the same for post-vaccination and post-infection. We fully expect this guidance to be updated in the future.