Varapalo from the experts to Darias for the cocktail of doses: "insufficient test", "political decision"...

The AstraZeneca Vaccine Questions against Covid they don’t end. The Ministry of Health has finally decided this week that those under 60 who already have a first dose receive the second from Pfizer. But he has admitted that those who for some reason do not want to do so, sign a consent to receive the second puncture also from AstraZeneca.

This has generated many doubts about which is the best decision. Experts consulted by 20minutos have made a balance of the pros and cons of each of the options, although they have pointed out that the most important thing is to already receive a second dose, because the maximum interval between them, 12 weeks, has been exhausted. They have also criticized that the study on which the Government has based its decision, although good, It is insufficient.

The Health decision is based on the preliminary results of the Combivac study, made by the Carlos III Institute to analyze the effect it has on a patient two different vaccine doses. A study started after doubts about AstraZeneca (now called Vaxzevria and developed at the University of Oxford) by some cases of thrombosis after the puncture. In Spain the death of at least three people has been registered in these circumstances

Both the European Medicines Agency (EMA) and the WHO have certified the safety of the vaccine and have indicated that their The benefits far outweigh the possible risks. The European agency, however, did find a link between Vaxzevria and cases “extremely rare “thrombosis.


These cases, which have occurred in an approximate proportion of one in a million, aroused doubts among the population, who began to reject it. In fact, Spain has banned its application in children under 60 years.

The question was what was going to happen to the people minors first vaccinated with AstraZeneca. fundamentally essential workers such as police, firefighters and teachers.

This is the question that the Combivacs study tried to answer, since the two vaccines are of different technology: viral vectors in Oxford, messenger RNA in Pfizer. This Thursday the Minister of Health, Carolina Darias, presented the results to other EU counterparts at the Informal Health Council.

An insufficient study

Adelaida sarukhan, PhD in Immunology and Scientific Writer of the Barcelona Institute of Global Health (ISGlobal), a center promoted by the LaCaixa Foundation, points to 20minutos that this type of essay is important “because in the future we will need more flexibility and if we don’t have enough availability of a vaccine, we can put another one as a second dose. “

Adelaida Sarukhan, PhD in Immunology and Scientific Writer at the Barcelona Institute for Global Health (ISGlobal),

Adelaida sarukhan

  • PhD in immunology and scientific editor of the Barcelona Institute of Global Health (ISGlobal),

However, it adds to the criticisms made by other scientists after knowing the Combivacs results:

“It is not the trial that can truly guide the decision to put a second dose of Pfizer or AstraZeneca”

Comparison of approved vaccines against Covid-19.

“It is not the trial that can really guide the decision to put a second dose of Pfizer or AstraZeneca, and we already knew this, because it is a small, phase 2 trial, the only thing that is analyzing, because it is the only thing that has given time to have seen, is that a good level of neutralizing antibodies, which are the ones that matter most to us, after a second dose of Pfizer. “

Results that were already expected. But there is still no data on the effectiveness of combining two different vaccines. Efficacy measures the protection that the serum develops: in the case of AstraZeneca it is close to 80% while for Pfizer it is 95%.

Reactions to mixed vaccine

“I don’t want to downplay the essay, but I don’t think it gives many elements to make a decision based on evidence, because it is not giving us efficacy “, Sarukhan points out.” It tells us that a good level of antibodies are produced; it also gives us an indication that immediate side effects are no worse of what we are seeing with these vaccines, such as fever or arm pain, which is always a good indication. “

“But there are no efficacy results, which are the ones that show whether people are protected from the disease or not. And you can’t see because there are very few participants and not enough time has passed. “

Does not answer the question

Salvador Macip, Research physician at the University of Leicester and professor at the Universitat Oberta de Catalunya, it also agrees that the study does not answer the question that it was intended to answer.

and professor at the Universitat Oberta de Catalunya, vol

Salvador Macip

  • Research Physician at the University of Leicester

Professor at the Open University of Catalonia

“What we wanted to know is whether to give the second dose AstraZeneca is better, worse or the same to give it to Pfizer, and the study does not analyze this because it is small and is not designed for that “.

“What the study says is that mixing vaccines gives you antibodies, an expected response that is good to know because it has not been studied before, but this does not mean that it works worse or better to give the second dose with the vaccine that touches, “he adds,

An ideal studio

Sure enough, the study released Tuesday noted that people who received a second dose of Pfizer increased their IGG antibody levels up to 150 times with respect to those who did not inject it. The ability of the former to neutralize the virus increased between “seven and seven and a half times” with respect to the latter,

To have good efficacy data, Sarukhan estimates that another study, phase three and larger, and lasting one to two more months, would be needed. 400 people have participated in Combivacs, while other studies of phase 3 have required 20,000 or 30,000 subjects.

In addition, the study of Carlos III did not have a control group, that is, vaccinated with a second dose of AstraZeneca, to compare the results of the two groups.

“Why did you decide not to do this group with AstraZeneca? I don’t know, I suppose to avoid any negligible risk”

“Why did you decide not to do this group with AstraZeneca? I don’t know, I guess to avoid any negligible risk“he comments.” There is a huge aversion to risk, in general in Europe, and some decisions are more political than scientific, and perhaps for this reason they decided not to do this control group, which in fact in England is what what are they doing”.

The authorities have clarified that these results are preliminary, and that Combivacs will continue to operate during one year to give definitive results.

“We think so, the combination will most likely work because good antibody levels are being produced, and the neutralizing antibody level correlates relatively well with protection, but we can’t be sure either “right now, says Sarukhan.” As always in science, the important thing is to have the data. “

A larger study is underway in the UK, with more participants, for a longer time and analyzing different combinations applied in various terms.

Macip also foresees that mixing vaccines can work, but insists that at the moment there is no data to confirm it “We will know in a few months when let’s have the british study underway and that is done to answer this question. “

And what vaccine do I get?

The million dollar question for citizens first vaccinated with AstraZeneca: Stick with it or switch to Pfizer? Sarukhan admits that in the case of AstraZeneca there is the safety issue with the very rare cases of thrombi, which have not been seen at Pfizer. So the patient who chooses to combine would be sure to eliminate even that tiny risk of thrombosis.

On the other, the effectiveness of two doses of AstraZeneca already tested, which is not yet confirmed with the combination. Macip cites those reasons to stick with AstraZeneca. “It is a public health decision that has to be made with solid scientific data, and at this time we only have data that guarantees that the second dose of AstraZeneca works, the rest are assumptions.”

“It is the Government that has to make the decisions, it is not fair that this should be passed on to the citizen”

In fact, the researcher, who will receive his second dose of AstraZeneca in a few weeks, criticizes that the choice is left in the hands of the citizen. “It seems like a bad idea to me, we don’t have to pass this responsibility on to him,” he says. “It is the Government that has to make decisions with the data that are available and in a scientific and reasonable way, it is not fair that this is passed on to the citizen, who does not have the preparation to make this decision.”

Be it one or the other, Sarukhan warns that the second dose already has to be put, because time is passing and the maximum interval between punctures is being exceeded. Already Sanidad extended it from 12 to 16 weeks to give more time to finish the study.

“The most important thing is that, be it one or the other, the second dose is already given,” emphasizes the researcher. “This delay in deciding what to do is that many people are already exceeding the interval and there yes we enter very unfamiliar terrain, because no clinical trial has gone further. “


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