You are currently viewing Will we have to get used to mixing vaccines?  It is "reasonable" Y "habitual" in animal health

Now that the nearly 1.7 million essential workers under the age of 60 who received the first dose of AstraZeneca and these days they have to choose to complete their pattern between Pfizer (as recommended by the Ministry of Health to minimize risks of thrombi) or AstraZeneca (as recommended by the European Medicines Agency and Communities such as Madrid, Andalusia or Galicia), it may be a good time to review what is known about heterologous vaccination guidelines, that is, about mixing punctures against the same virus.

According to experts in immunology, combining vaccines can elicit a stronger and longer-lasting response, as well as protect against new variants of the virus. In addition, it would facilitate the delivery of doses between countries.

Every year they are vaccinated against gripe in Spain about 5.5 million people at risk (elderly, pregnant and health care, mainly), that is, 54.2% of those over 65 and 19% of those over 15, according to the data of OTHER. However, until now no one had thought to ask if the one-year vaccine had been developed by the same pharmacist or with the same technology as the one that had been administered in previous years. And it is that, until now, we have not experienced a worldwide vaccination campaign followed almost minute by minute by the scientific community, the media and the population.

According to Isabel Sola, the co-director of the coronavirus laboratory of the CSIC’s National Center for Biotechnology, mixing vaccines is “an idea reasonable“In recent years, in fact,” is what habitual“in vaccine research for diseases of animal health.

The scientist, who is developing one of the three vaccines being prepared in Spain against covid-19, explains that mixing different sera makes particularly sense with viral vector vaccines (such as AstraZeneca or Janssen) and explains why: “Usually the second dose is not the same viral vector because the heterologous regimen works better than the homologous one., because vaccines that are a viral vector carry a vehicle that is the adenovirus and that vehicle carries information from the ‘S’ protein of the coronavirus as a passenger, but when that is administered to a person, the immune system detects something strange that is both the ‘S’ protein like adenovirus and generates an immune response against all that. And, when administering the second dose, what happens is that if there is already an immune response against the vehicle, it cannot turn on as well because the immune system is launched against it. Let’s say that the vehicle, with the second dose, is unable to deliver the passenger it had to deliver because before the immune system has already neutralized it. So Information should be presented in two different ways for maximum efficiency“.

The Russian Sputnik vaccine, “uses two different adenoviruses, 26 in the first dose and 5 in the second”, which is similar to a heterologous regimen

Isabel Sola points out that for this reason, the Russian Sputnik vaccine, “uses two different adenoviruses, 26 in the first dose and 5 in the second “.

In contrast, combining vaccines of the same nature, such as AstraZeneca and Janssen, “would not make the same sense.” In this case, you would not expect to get benefits, but the answer would be similar to administering AstraZeneca twice or Janssen twice, he says.

In the same vein, the president of the Spanish Association of Vaccination, Amós García, also spoke last Friday in an interview on Channel 24 hours of TVE, in which he stated that “probably the message was not transmitted correctly that what appears as unknown, which is the possibility of administering Pfizer as a second dose, is not an unusual practice in the world of vaccines. Carrying out heterologous guidelines, that is, using different vaccines in the same person to prevent a disease, is a frequent practice in medicine and we already use it in our country against certain diseases“.

Already tested in HIV trials

The VIH, the virus that causes pageIt is “complicated” and science has yet to come up with a vaccine that works. However, experimentation has also been directed towards combining vaccines. “The heterologous pattern is the one that is shown to work better,” says the CSIC scientist. Dr. Pierre Meulien, Executive Director of the European Initiative for Innovation (IMI), spoke in the same vein in the European Commission’s research magazine Horizon: “This is not a completely new way of thinking. We have decades of experience in preclinical and clinical (work), especially in HIV, using these approaches.”

What is new about the situation caused by the coronavirus? Sola states that “all the vaccines that had been tested so far used to combine DNA with a viral vector”, but now a new component enters the scene: vaccines based on Messenger RNA, such as those already approved by Pfizer / BioNTech and Moderna, or the still under review CureVac. Therefore, the scientist underlines “the need for clinical trials to confirm” the safety and effectiveness of combinations with these new vaccines.

Studies in progress

UK a study began in February to evaluate four different combinations between Pfizer and AstraZeneca vaccines whose preliminary results showed that adverse effects were more frequent, although mild. “(This study) seemed very timely because it allowed greater flexibility when it comes to having vaccines and because the heterologous regimen can work better than the homologous one, this is what has been seen in animal experimentation.”

Archive image of a sign pointing to a vaccination center in London.

With a smaller sample, the Carlos III Health Institute of Spain compared the administration of one dose of AstraZeneca against one of AstraZeneca and a second of Pfizer and the preliminary results also showed that the side effects were those already seen (headache and discomfort, also mild) and that the immune response was increased.

Last week, the United Kingdom, one of the countries with the most advanced vaccination campaign, announced that it will study 3,000 people vaccinated with AstraZeneca and Pfizer (the two vaccines it has used) a third booster dose of up to seven different pharmaceutical companies with the aim of protecting those most vulnerable to covid for next autumn.

Third dose

At the moment, only the almost two million essential workers have found themselves in the position of having to, if they choose, combine vaccines. But perhaps this situation will be replicated to a larger population for next autumn. Are already Pfizer and Moderna the companies that have raised the need for a third dose reinforcement.

Asked about this question, Isabel Sola affirms that we are going to have to get used to the vaccine cocktail, “always with a clinical trial in between that confirms with evidence a hypothesis that is very reasonable” given “the prior knowledge we have about how they work. This, he continues, “will not mean that anything is lost, on the contrary, the efficacy could be better, but it must be shown that the efficacy of each particular combination is at least the same or better and the safety, that which is required by any vaccine. “

“To think that it can be eradicated like smallpox is a less realistic scenario”

The biologist adds that she is considering that the covid vaccine, in the future, if reimmunization is necessary, to be administered in a multipurpose way, that is, “that in the same vaccine it is protected against several viruses, such as influenza or coronavirus”, just as it is done with other vaccines such as those of the children’s calendar (the triple viral, for example).

Given that SARS-CoV-2, the virus that causes covid-19, infects asymptomatically and also has reservoirs in nature (bats), from which very similar coronaviruses emerge, “thinking that it can be eradicated like smallpox is a less realistic scenario“admits Sola, who believes that” it will be necessary to think that as immunity increases in the population, a balance of strength will be reached as with other coronaviruses for which nobody cares and we do not even have to vaccinate ourselves.


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