Health Ministry to give Pfizer second dose to those under 60 vaccinated by AstraZeneca

Health and autonomous communities debate after clinical trial supports the combination

5 min
Vaccination with AstraZeneca this week at UB.

MadridPeople under the age of 60 vaccinated with a first dose from AstraZeneca will receive a second dose from Pfizer if the Ministry of Health's proposal goes ahead. The public health commission continues to debate this possibility and it will have to be ratified on Wednesday by the Interterritorial Health Council, which is made up of the Ministry of Health and the health ministers of the autonomous communities. The decision, however, will not be unanimous because governments such as those of Madrid and Andalusia are in favour of completing the guideline with AstraZeneca.

In total, 4.8 million Spaniards have received a first dose from AstraZeneca and only 544 have the full regimen. The vast majority, therefore, expect to complete the vaccination: those over 60 would do so with the same drug and those under 60 with the Pfizer drug. This second group comprises some two million people throughout Spain. The unknown will be resolved once the first vaccinated - in mid-February - have to receive the second dose. On 7 April the campaign with AstraZeneca was stopped and later it was decided to delay the period between the first and second dose from 12 to 16 weeks. Pfizer's alternative also comes after the EU decided not to renew procurement contracts with the Anglo-Swedish company because of delays.

The health ministry presented itself at this afternoon's meeting with a study under its arm that endorsed the new combination: the CombivacS clinical trial, coordinated by the Carlos III Health Institute (ISCIII). "The conclusion is that the administration of a booster dose is effective and safe", said the coordinator of the clinical network of the ISCIII, Jesús Antonio Frías, this morning at the presentation, prepared with the aim of seeking alternatives to the vaccination with AstraZeneca, which, in exceptional cases, caused thrombosis.

Researchers have released preliminary results and explained that the number of neutralising antibodies in a person vaccinated with AstraZeneca who receives Pfizer's second dose is seven times higher than with the first dose alone. The increase is already significant seven days after the second injection and remains stable at 14 days. The study is based on a comparison of Pfizer second-dose vaccinees and non-vaccinated second-dose vaccinees, so the scientists did not want to say whether a Pfizer second dose is better than an AstraZeneca second dose. A recent study published in the journal The Lancet and carried out in the UK found that in this case the number of antibodies is multiplied by five, but experts have pointed out that it is not appropriate to compare the two studies because the age ranges of the sample vary.

The Spanish study, which also involved the Vall d'Hebron and Clínic hospitals in Barcelona, looked at a total of 663 people in two different age groups: 18-49 years old and 50-59 years old. A total of 442 people were given the second Pfizer dose between 8 and 12 weeks after receiving the first dose from Astrazeneca, while the remaining 221 did not receive the new vaccine. In the choice of the sample, anyone who had previously been infected with the coronavirus was left out. In the presentation of the results on Tuesday, it was not explained whether the increase in antibodies varied according to age, but the researchers said that "there were small differences". The Madrid regional minister, Enrique Ruiz Escudero, considered the sample size to be low and questioned the study in order to maintain his firm position to continue vaccinating with AstraZeneca.

No serious collateral damage

The other leg of the clinical trial focuses on the possible collateral damage to people who received the second dose of Pfizer. The conclusion drawn by the head of the preventive medicine and epidemiology service at Vall d'Hebron, Magda Campins, is that the symptoms that appeared were mostly mild. No one required hospitalisation. Some pain at the injection point did occur in 88.2% of cases, as well as headache (44.4%), malaise (41.7%) and, to a lesser extent, chills (25.4%), nausea (10%) and cough (7.4%). Only 11 people out of 442 had a fever.

This last data is significantly different from the results of the study published in The Lancet a few days ago because it recorded 34% of people who had fever. Campins stressed that the British trial mostly included people over 50 and the timings before administering the second dose also changed. While in the Spanish trial it was between 8 and 12 weeks later, in the UK trial it was 28 days later.

What is being done in Europe?

If the decision is finally made to give Pfizer's second dose to people who received AstraZeneca, Spain will follow in the footsteps of France - which combines vaccines for those under 55 - and Sweden and Finland - which mix them in the case of those under 65. However, and according to some members of the scientific community, the CombivacS study should not be decisive in deciding which people can be given AstraZeneca's second dose.

Margarita del Vale, a virologist at the Spanish National Research Council (CSIC), also defends the administration of the second dose of AstraZeneca to those who have already received the first dose. "The evidence for two doses of the same vaccine is more solid because of the pharmacovigilance and safety monitoring of millions and millions of people," she says in an interview with ARA.

While the expert believes that the combination of vaccines is not inconsistent, she points out that it has to be based on good evidence, and that the study with 600 people is not comparable to data obtained in other countries such as the UK or Israel, reports Maria Garcia. "It doesn't pay off. We have very good vaccines and, despite the fact that there is no zero risk, we have to put the risks right and assess the benefits. And the very powerful evidence of the follow-up of millions of people is above any other safety issue", she insists.

The infectiologist Oriol Mitjà also defends injecting the second dose of this vaccine to people who received the first "and had no complications", since, he says, the risk of thrombosis with the second dose (one case per million vaccinated) is much lower than with the first (11 cases per million inhabitants). "Second doses should be given without further delay or hesitation", he says.

However, Mitjà admits that in a scenario of agile vaccination it is "reasonable" to stop the inoculation of first doses of AstraZeneca - he goes so far as to say that this vaccine is "doomed to disappear" - in favour of "safer alternatives" such as messenger RNA vaccines (Pfizer and Moderna).

And this is what Portugal is doing, offering the younger 60-year-olds the second dose of AstraZeneca but also giving them the option to receive another vaccine after 12 weeks. Or the UK, where the Anglo-Swedish vaccine has been the cornerstone of the vaccination strategy but now the UK population under 40 can choose whether they want to receive it or opt for any of the other vaccines available.

Also Germany, which initially planned to give Pfizer as a second dose, is now giving AstraZeneca to all those vaccinated with the first dose regardless of age, as was the case in Italy. In addition, the German government offers it without age restrictions to anyone who wants to get it and has not yet received any vaccine.

In contrast, Denmark and Norway decided not to use AstraZeneca's vaccine for their vaccination campaign.