Five keys to understanding why some countries are starting to combine COVID-19 vaccines

Based on the distribution and delivery of COVID-19 vaccines around the world, some countries have already decided to combine doses prepared on the basis of different platforms and laboratories. There have been delays in vaccine delivery and fears of potential side effects that have caused them to adjust vaccination plans which are primarily aimed at reducing the risk of complications, hospitalizations and death. But the strategy is still being studied.

The combination of vaccines (which they call in English “mix match “) it had been implemented with other diseases before. Now it has started to be authorized with the two doses of the initial regimen, or as a back-up as a third dose. On June 1, Canada’s National Advisory Committee on Immunization announced that people who received the first dose of AstraZeneca vaccine may choose to receive a different vaccine for their second dose. He added that the Pfizer / BioNTech and Moderna messenger RNA vaccines can be used interchangeably.

France, Germany and Finland have also adopted measures facilitating the exchange of vaccines. In the case of France, it was decided that people under 55 who received the AstraZeneca vaccine in the first dose can access a messenger RNA vaccine in the second dose. Finland has decided the same for people under 65. It has also been implemented by Norway and Sweden.

In the United Arab Emirates and Bahrain, which is located on the east coast of the Persian Gulf, it was decided that the Pfizer / BioNTech vaccine would become available to people initially immunized with a vaccine developed by Sinopharm as a booster vaccine.

Ya se han registrado más de 3,7 millions de muertes por COVID-19 desde los primeros deportes de casos in diciembre de 2019. Si bien las vacunas se desarrollaron en menos de un año, aún el proceso de vacunación marcha lento, especialmente en los developing countries. As of June 5, only 1.9 million doses had been applied worldwide, according to the World Health Organization (WHO). In this context, here are 5 keys to understand why the vaccine combination is decided and what are the objections that have been raised so far.

1- The combination of vaccines has a history with good results for other diseases

Mixing doses of different vaccines may seem unusual, but for immunologists this is nothing new. HIV researchers have long explored this possibility of vaccination against HIV. This is because protection against the HIV virus requires a complex immune response that would be almost impossible to achieve with a single type of vaccine, as they tend to produce only one type of immune response or stimulate a single set of immune cells. Although an effective vaccine against HIV is not yet available, the most effective vaccine developed to date used a combination of different types of vaccines.

The Ebola vaccine developed by the company Johnson & Johnson is also an effective mixed vaccine currently in use. It was chosen to provide long-lasting immunity. The first injection uses the same adenoviral vector as the AstraZeneca vaccine, and the second uses a modified version of a poxvirus.

2- The combination of vaccines can make the immune response more robust

Earlier this year, the makers of the AstraZeneca vaccine investigated the possibility of combining a first dose of their vaccine with a second dose of the Russian Sputnik V vaccine. Both vaccines use an adenovirus (the common cold) as the delivery system for introduce the coronavirus antigen. in the human body and cells.

But the immune system can create immunity not only against COVID-19, but also against the adenovirus which is used as a vector. This means that after a second dose of the same vaccine, the body may have antibodies to the adenovirus component that could neutralize the vaccine, making the second injection less effective, Priya Joi said, on the official website of the Alliance for Vaccines. , which is known as GAVI, which is a collaboration between WHO, the Bill and Melinda Gates Foundation, UNICEF and the World Bank.

In Spain, the CombivacS study is underway. A combination vaccination schedule is evaluated using a second dose of Pfizer / BioNtech vaccine (called Comirnaty) in people under the age of 60 who have received a first dose of AstraZeneca (Vaxzevria). They already have the first results of cellular immunity. Although the clinical trial is continuing, the researchers have published the results of the follow-up 14 days after the second application. Its parameters indicate that the combination of these vaccines is safe and effective.

“The future would be to combine COVID-19 vaccines based on different platforms and even combinations of vaccines based on the same platform would be made,” said Angela Gentile, vaccine specialist at the Argentine Pediatric Society and the National Commission for Vaccine Safety, consulted by Infobae a few days ago. “If the coronavirus becomes endemic like the flu every year, it is possible that different doses of the vaccine will need to be combined. The evidence from the study in Spain is encouraging: it could be extrapolated to other vaccines based on the same platforms. Humanity today needs both to combine vaccines and to have more doses in the context of a tragic and surprising pandemic ”.

3- The vaccines that could be combined are still being studied

In the UK, the company Novavax announced on May 21 that it would participate in a mixed vaccine trial to test the use of an extra dose from another producer as a booster. The rehearsal will begin this month. In addition, the first results of a study by the University of Oxford, published on May 12, indicated that people who received the Pfizer vaccine followed by a dose of AstraZeneca, or vice versa, were more likely to have mild or moderate common symptoms. after vaccination only if they received two doses of the same type. This investigation is continuing. They started it because they wanted to be prepared for a possible lack of vaccines.

Meanwhile, in the United States, the National Institutes of Health (NIH) announced on June 1 that they had started a clinical trial in fully vaccinated adults to assess the safety and immunogenicity of a booster of a different vaccine.

4- There are doubts about what would happen if they needed reinforcements due to the appearance of variants

Daniel Altmann, immunologist at Imperial College London, told the magazine Nature that a strong immune response resulting from the vaccine combination strategy is “fully predictable from basic immunology”. But he wondered what would happen if people needed a third dose to prolong immunity or protect against new variants of the coronavirus. Repeated doses of virus vaccines, like the one from Oxford-AstraZeneca, tend to be less and less effective because the immune system generates a response against the adenovirus. RNA vaccines, on the other hand, could trigger stronger side effects with additional doses.

5- It is better today to cumulate the doses of vaccines before not being vaccinated

Ignacio López-Goñi, professor of microbiology at the University of Navarre, considered that in view of the debate taking place around the world on the benefits and risks of combining different doses of vaccines: “It’s better to get vaccinated with a second dose of anything than to end up with just the first. We must be more afraid of the virus than of vaccines ”.

For the specialist, both the studies which were carried out in the United Kingdom and that of Spain have evaluated only the mild side effects which appear 24 to 48 hours after the vaccination and the production of neutralizing antibodies. “They are not used to assess these possible serious side effects which occur at very low frequency,” López-Goñi said in The conversation.

‘The best would be to look at the data provided by the UK, where they have already vaccinated around 6 million people with the second dose of AstraZeneca and have observed 6 cases of serious side effects, less than 1 per million vaccinated . Or just follow the recommendation of the experts, the European Medicines Agency (EMA), the WHO or the report of seventeen scientific societies that continue to recommend giving the second dose of AstraZeneca to people under 60 ”.

In Europe, several countries have decided to join forces considering a low potential risk of the AstraZeneca vaccine causing thrombosis. However, according to scientist López-Goñi, “AstraZeneca continues to be an effective and safe vaccine”. He believed that there was a poor communication of the risks of side effects which generated mistrust in people. The WHO and the European regulatory agency have clarified that the benefits of this vaccine outweigh its risks.

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