Vaccine mix after AstraZeneca, in which countries is it used? The situation in Europe (and the case of Canada)

Vaccine mix after AstraZeneca, in which countries is it used? The situation in Europe (and the case of Canada)
Vaccine mix after AstraZeneca, in which countries is it used? The situation in Europe (and the case of Canada)

The mix vaccinale, ie the possibility of using different vaccines for the two doses, is already used in different ways in other countries than in Italy. The Italian Medicines Agency (Aifa) has approved “mixed vaccination for subjects under 60 who have received a first dose of Vaxzevria” (AstraZeneca). And the former director general of the European Medicines Agency, Guido Rasi, recalled that in “Countries such as Germany, Spain and France and even Great Britain have already adopted heterologous vaccination, so Italy would not be the only one to undertake this approach “. But Canada and Finland have also followed the same path, establishing that those who have received AstraZeneca can use Pfizer or Moderna for the second dose. In South Korea, on the other hand, a trial on the alternating use of AstraZeneca, Moderna or Pfizer has been started. And China is moving forward with a series of Covid vaccine alternation studies developed in the country. In Canada, for example, “those who have received a first dose of the AstraZeneca product can use Pfizer or Moderna for the second,” explains the country’s health agency. Similarly, the two immunizations based on mRna technology, namely Pfizer and Moderna, can be alternated between the first and second dose. However, the Canadian authorities have also pointed out that it would be “optimal” to use the same vaccine for both doses.

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Mix vaccines, virologists – Roberto Cauda, ​​full professor of Infectious Diseases at the Gemelli Polyclinic in Rome reassures: «In other European countries, such as France and Germany, they are already using the vaccine mix system by making the second dose different from the first. It is right to open a debate, but there are no safety or efficacy reasons that jeopardize this system, also because it is not the first time that a heterologous vaccination has been made. Now that we are in a phase of lower circulation of the virus, in a logic of prudence, it has been decided to set the level of 60 years, which is not the same for all countries, below which the mix can be made . Among other things, a suitable period of time is maintained between the two doses, from 8 to 12 weeks. Furthermore, since one type of vaccine has a greater effect on antibodies and the other on cells, heterologous vaccination could also give better results than the single dose ».

Mix vaccines, so Hope – A thesis based on the comparison with other countries that has already been advanced by the Minister of Health Roberto Speranza: «Heterologous vaccination has already been used by important countries such as Germany for several weeks and the results are encouraging. There are some studies that testify that the immune response is even better than that with two doses of the same vaccine ». And confirmed by the Undersecretary of Health Pierpaolo Sileri: “In various countries of the world, including Canada and Germany, the mix of anti-Covid vaccines is already being made,” which is safe and there are no risks, if not a modest increase in minor adverse reactions “.

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Mix vaccines, studies – Various countries have launched studies to verify the effects of these mixes between products, which would use vaccines that are different from the first immunizations received. New research has started at the US National Institute of Health (Nih): out of 150 fully immunized volunteers who had received one of the three vaccines approved in the US (J&J, Moderna or Pfizer) a booster of a different brand will be tested. A note from the Nih has made it known that the first objective of the investigation will be to verify the safety and immune power of the new regime. The participants will be followed for a whole year but the first results should be achieved by the end of the summer. Furthermore, the heterologous vaccination approach, according to Aifa, “is supported by the data deriving from two clinical studies conducted respectively in Spain (CombiVacS) and in England (Shaw RH, Lancet 2021) and which show good results in terms of response antibody (CombiVacS) and safety in terms of acceptability of side effects ».

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Mix vaccines, the Spanish study – According to the Spanish Combivacs study, not yet published, the heterologous vaccination program is safe and effective. Combivacs enrolled 670 participants aged 18 to 59 who had already received a dose of AstraZeneca: Those who received a second dose of Pfizer vaccine, 450 subjects, showed a 150-fold increase in antibody titers, which remained evident seven days. after administration. However, the same authors point out that more data from larger studies are needed to confirm immune responses. The other study whose preliminary data have just been published in Lancet (the English research called Com-Cov on 830 subjects over 50) has instead shown that the mix with a first dose of AstraZeneca and the second with Pfizer causes an increase in reactions mild adverse events such as fever, headache and pain, with “some short-term disadvantages” mitigated with the use of paracetamol. These side effects were reported in 34% of the sample, compared to 1.7% in the Spanish study. However, Lancet notes at the same time, “it is reassuring that these symptoms were short-lived and that there were no concerns from the limited haematological and biochemical data available” relating to rare thrombosis. On the other hand, data on immunogenicity and antibody response are not available, expected by June. Also in Italy, at the Spallanzani Institute in Rome, a trial on the second dose started last April, after the first with AstraZeneca, using other vaccines including Sputnik.

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Mix vaccines, the perplexities – However, some experts continue to be perplexed. To date, Nino Cartabellotta, president of the Gimbe Foundation noted, “the only scientific evidence we have, in addition to both immunological and biological rationale, are 4 small studies that have enlisted a total of a thousand patients that demonstrate that the reaction after the mix of vaccines is good and there are no relevant adverse effects. But the scientific evidence on this topic is still preliminary and maintains a certain margin of uncertainty ».

Tuesday June 15, 2021, 12:01 pm – Last updated: 16:28

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