The massive demand to repeat a second injection with the AstraZeneca formula among the almost two million essential workers, aged under 60 years old, is threatening to jeopardise Spain's stock of the vaccine and lead to a shortfall in supply.

The Ministry of Health is warning that it is "almost impossible" to make accurate forecasts because it is difficult to calculate how many of those hundreds of thousands of teachers, police, military personnel or firefighters will choose to reject the second jab with Pfizer - the one officially recommended by the department - and choose AstraZeneca again.

Despite insisting that a second vaccination with the AstraZeneca formula should only be administered in "exceptional cases", in practice it is being totally ignored in the regions where the re-vaccination of this group has already begun.

According to the first estimates, in the regions such as Murcia, Andalucía, Galicia and Catalonia between 70 and 90 per cent of the people are choosing not to mix vaccines and instead are having a repeat jab with the AstraZeneca formula.

If that uptake is mirrored nationally then there will be an issue as almost all of these nearly two million essential workers are at the 16-week limit set by the Ministry of Health for their second vaccination. And there are also approximately 2.8 million other people, mostly in the 60-69 age group, who received their first injection with the AstraZeneca formula andfrom this June should be jabbed again.

Only 2.3 million doses for, potentially, almost five million people

And that's where serious problems can arise if AstraZeneca, which has suffered from some supply issues in the past, doesn’t deliver.

This Friday morning (28 May), there were only 987,693 AstraZeneca doses in reserve. Provided that the laboratory complies, another 1.3 million vials should arrive in Spain next Monday making a total of 2.3 million doses. However almost five million people could be queuing up for the second vaccination with AstraZeneca if the essential workers, under 60, choose the Oxford formula.

This Wednesday Spain’s Health Minister Carolina Darias - before learning that most of those affected were opting for AstraZeneca - said she was convinced that there would be no supply "problems". But just 24 hours later, her department said they were not so sure faced with the flood of requests to repeat the second vaccination with the same formula.