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I have the option of a second dose of the Pfizer vaccine after having had the AstraZeneca: What should I do?

Around 1.5 million essential workers in Spain will be faced with this choice, after cases of rare blood clots were linked to the Anglo-Swedish medication. Experts respond to questions about the best course of action

A second shot of AstraZeneca is administered in a sports stadium in Murcia, southern Spain.
A second shot of AstraZeneca is administered in a sports stadium in Murcia, southern Spain.Marcial Guillén / EFE

Carlos Agudo, a 35-year-old pharmacist who works in Jaén, southern Spain, is one of the 1.5 million essential workers aged under 60 who was given a first dose of the Oxford-AstraZeneca Covid-19 vaccine, and now finds himself in a situation he “never could have imagined.” On Thursday, he has his appointment for a second dose, but will be able to choose whether to opt for the Anglo-Swedish medication, or the vaccine from Pfizer-BioNTech. “With so many ups and downs, they’re even making us have doubts, and we’re healthcare professionals,” he complains. “I don’t even want to think about the teachers and others who are in the same situation.

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“My option and that of many colleagues is to continue with AstraZeneca because that is what the technical notes of the vaccine say,” he explains. “But of course, it is surprising that we have to sign a prior consent form because if you read it, it’s as if it was made to put you off. It’s even more difficult to understand when you know that the risk of blood clots is much smaller with the second dose than with the first.” Agudo concludes with a recommendation: “Whatever the case, you must get vaccinated. We should all do it. No one should stay at home because of all these changes.”

Here are answers to the frequently asked questions about the troubled path of the AstraZeneca vaccine.

Can I really choose between AstraZeneca and Pfizer in Spain?

Yes, but this is only applicable to the essential workers aged under 60 who already got their first dose of the medication, which was found to be linked to very infrequent but serious cases of blood clots. The Health Ministry and a number of Spanish regions, however, are trying to avoid presenting this option as a choice. The reason for this is to avoid breaking one of the basic principles of the vaccination campaign in Spain: people cannot choose which vaccine they will get and each citizen should take what they are offered. This is why the process is being formally presented as two steps. In the first, the citizen rejects the second dose of Pfizer, which is the first option for people in this situation. In the second step, a second dose of AstraZeneca is offered and the citizen accepts it by signing an informed consent form recognizing the risk of blood clots.

Why do I have to sign this form?

This decision was taken by the regions and the Health Ministry, despite division within the Public Health Commission on the way to proceed and delays that saw some recipients miss the 12-week deadline for their second shot. Most experts, however, don’t see the sense in this approach. “It’s not being done with any other vaccine and it is the second dose of a vaccine that’s been approved by the European Medicines Agency (EMA), so requesting [a signature] is to convey to the citizen that they are taking on an unusual risk, and this is not the case,” says Quique Bassat, an epidemiologist and researcher at the ISGlobal institute in Barcelona. Some regions are taking a different route, however, such as Andalusia – the health authorities in the southern territory will have a document prepared for each vaccine, but will not force citizens to sign them. The reasoning is that if someone turns up voluntarily for a vaccine shot, it is understood that they are in agreement with the vaccination and this will be registered with the healthcare professionals. The Health Ministry, meanwhile, has pointed out that all the agreements reached on the second dose – including this one – are obligatory and that the important thing right now is to generate confidence among citizens. The best way to do this, it argues, is to “comply with” what has been agreed.

What does taking the second dose of AstraZeneca involve?

Ángela Domínguez, a vaccine coordinator at the Spanish Epidemiological Society (SEE), argues that this option is very safe. “The EMA has analyzed the registered adverse events [involving blood clots] and concluded that there was no reason not to recommend the vaccine,” she explains. A month ago the EMA recommended administering the second dose to those who had already had the first. What’s more, Domínguez points out, the majority of cases of an adverse reaction were detected after the first shot. “For every million [doses], there were 3.4 thrombotic adverse effects, a figure that falls to fewer than one per million for the second dose,” she says. The Health Ministry and the regions that voted in favor of offering a second option, however, argue that while it is tiny, the risk does exist.

What if I opt for the Pfizer?

Amós García Rojas, the president of the Spanish Vaccinology Association, argues that this is the best option given that the vaccines that use the RNA messenger technology (i.e. Pfizer and Moderna) have been shown to have a better safety profile. Using two vaccines, he argues, “works, that’s something that we know well.” He cites a recent study carried out on the option by the Carlos III Health Institute in Madrid, “which showed that administering a second dose using Pfizer after a first dose of AstraZeneca is very efficient and safe.” But Quique Bassat points out that the option has not been “backed by any regulatory agency,” and that the evidence that supports it is still scant and based on just two studies. The first, preliminary results of which were published in the prestigious medical periodical The Lancet two weeks ago, stated that combining two vaccines increased the side effects – fever, muscle aches, fatigue – albeit still being very mild. The second, the aforementioned study at the Carlos III Health Institute, has been criticized for how its results have been used, and was carried out on a sample of just 600 patients. “This is not a phase 3 study,” Bassat complains, “with tens of thousands of patients studied. We still don’t have that.”

What have other countries done?

Amos García points out that France, Germany and Sweden, among other countries, “had no doubts and changed the second dose to use Pfizer for safety reasons.” Other governments, such as that of Italy, have administered AstraZeneca, and have not so far seen serious reactions. The United Kingdom has also opted to use the same vaccine for the second shot, but not for anyone under the age of 30.

Why do I have to decide in Spain?

This is one of the points that has been most criticized by many experts: the citizen must take responsibility for a decision that corresponds to the health authorities, creating a situation of uncertainty and possible vaccine hesitancy. The position of the Health Ministry is that the Public Health Commission already took a decision, to use the Pfizer vaccine, and that AstraZeneca can be used on an exceptional basis. Whatever the case, the experts insist, all of the Covid-19 vaccines are safe, they have been approved by the EMA, and their effectiveness is being shown by the drop in the number of coronavirus deaths and hospitalizations as their rollout continues.

English version by Simon Hunter.

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