Two EU countries have put time limits on the validity of vaccination certificates for inbound visitors as the question of the efficacy of COVID-19 vaccines over time is being examined by scientists globally.

Austria will only accept travellers who have been fully vaccinated within 270 days of travel. For Croatia, those who received their second shot within 210 days of travel will be allowed entry.


This means that travellers who have received their second shot during August, for example, will be able to visit Austria up to a date in May 2022, and Croatia only up to a date in March 2022.

Several governments, including the US and the UK, are now mooting the idea of booster jabs, after it was found that the immunity afforded by vaccinations appears to recede slightly over time, although the vaccines’ protection against severe symptoms remains high.

US federal health authorities have recommended booster shots for all adults already fully vaccinated with either Pfizer or Moderna vaccines (and possibly those immunised with Johnson & Johnson too), but there remains some scientific disagreement on this. The WHO has criticised the decision to give US citizens a third shot while most people around the world haven’t had even one.

The UK government says it will start a booster programme in September for those who first received vaccines originally.

The UK health authority has also said vaccines designed specifically for variants of concern would not yet be available by the Northern hemisphere autumn, but would be considered once they were available.

The question of mixing vaccines has been raised but a decision has not yet been reached (people receiving a different booster vaccine from that of their first and second shots).