MADRID: Spain is extending the gap between the first and second doses of AstraZeneca's COVID-19 vaccine to 16 weeks for people aged under 60, the government said on Friday, going beyond the 12-week maximum interval approved by European authorities.

Spain is the first country to diverge from the European Medicines Agency's authorisation and promote "off label use", which would not be approved by the regulator and would leave individual nations responsible for any possible side-effects.

The extension gives authorities more breathing space to determine the safest way to administer the vaccine, the health ministry said. Spain initially gave AstraZeneca shots to essential workers aged 18-65 before allowing only people aged over 60 to received the vaccine due to concerns about blood clots in younger people.

The EMA's approval for the vaccine is based on the second dose being administered between four and 12 weeks after the first. A 16-week interval has not been tested in any human trials.

AstraZeneca and the EMA did not immediately respond to requests for comment.

Spain's move to restrict use of the shot caused widespread uncertainty and meant some younger people who had already received a first dose have been excluded from getting a second. By extending the interval between doses, authorities will be able to evaluate the results of trials on mixing different vaccines before deciding whether those groups will receive a second AstraZeneca shot or another drug, the ministry said.

Spain's state-backed Carlos III Health Institute is investigating the effects of giving Pfizer and BioNTech's vaccine to patients who already received an AstraZeneca shot.