At the moment you have to fill a PLF (passenger locator form) at arrival so you can be tracked and people you met contacted in case you develop covid symptoms.
Considering Belgium specifically https://www.info-coronavirus.be/en/travels/:
Check which COVID certificate you have at www.covidsafe.be. In principle, you have applied for this before you left. There are three types of certificates:
A vaccination certificate proves that you have been fully vaccinated against COVID-19. You are fully vaccinated 2 weeks after your last vaccination dose and if the vaccine is EMA-certified or Covishield. From 1 September, vaccination certificates from non-EU countries will also be accepted in Belgium under certain conditions, pending their equivalence agreement with the EU.
A recovery certificate shows that you have recovered from COVID-19. You have a positive PCR test result no older than 180 days and you no longer need to isolate.
A test certificate is proof of a negative COVID-19 PCR test result that is less than 72 hours old or RAT test result that is taken the day before or the day of arrival.
I know.
I was also surprised (ENRAGED) to realize that our sanitary pass allow(ed) vaccinated people to attend mass events or restaurants or places where that pass is mandatory even if they have covid symptoms or are under quarantine.
Apparently US citizens undergo a mandatory tests at arrival and must be fully vaccinated. From: https://unitedstates.diplomatie.belgium.be/en/coronavirus-co...
As of November 8, 2021, all fully vaccinated persons are able to travel from Belgium to the U.S. The details on the proof of vaccination and the pre-departure COVID-test are explained on the website of the U.S. Department of State.
U.S. residents are eligible to travel from the U.S. to Belgium, if they are fully vaccinated and have a valid vaccination certificate. We recommend you take all available proof of vaccination with you when traveling, both the CDC card and – when available – State-issued certificates. Please note that airlines decide under which conditions they carry passengers. We recommend you enquire about those conditions before booking your flight.
Upon arrival in Belgium, travelers undergo a mandatory test on day 1 and on day 7. Depending on your vaccination status, you should stay in quarantine for 2 or 10 days. Unvaccinated travelers can only travel in very exceptional circumstances, listed here.
Only recently did the headlines went from "there a no scientific evidences for a third dose" to "WE NEED EVERYONE TO GET A THIRD DOSE ASAP".