EU states must use all of the vaccine options available to fight the coronavirus pandemic, and it is too early to tell if a particular type is best, the European Medicines Agency said on Thursday.
Several countries have limited use of "viral vector" shots such as those produced by AstraZeneca and Johnson & Johnson because of a link with rare blood clots, and opted for messenger-RNA vaccines, such as those from Pfizer-BioNTech and Moderna.
"We are still in a pandemic and it's very important that in this fight against this pandemic we use all the options we have available," said Marco Cavaleri, the agency's head of vaccines strategy.
Mr Cavaleri said it was then "up to member states how they use them in the best interest of public health".
The agency this week denied that he suggested dropping the AstraZeneca Covid-19 vaccine, even for people over 60 to whom it was currently limited in some countries.
On Thursday Mr Cavaleri said the episode was "rather unfortunate and essentially was a misunderstanding on many aspects".
He said it was "very difficult to say" which type of vaccine technology might prove the most preferred in future, and that all vaccines had "already been saving thousands and millions of lives".
"Whether in the future there will be a certain type of vaccine like the messenger-RNA, that will remain the main one or not [or] whether other platform technologies will remain as ancillary vaccine that could play an important role in controlling this coronavirus, is difficult to say right now," Mr Cavaleri said.
"We are just glad to have so many options."
The agency has authorised four vaccines: those developed by Pfizer and BioNTech, Moderna, AstraZeneca and Johnson & Johnson.
One of another four under review, Germany's CureVac, suffered a blow when interim trial results Wednesday showed it was only 47 per cent effective.
That falls below the agency's threshold of 50 per cent but Mr Cavaleri said "this does not mean that we will not look into the entirety of the evidence" before reaching a decision.
Meanwhile the regulator revealed that 17 million J&J doses were held back in the EU as a precaution after a batch in the US, made at the same time, was contaminated with material from another vaccine.