First dose with AstraZeneca vaccine and booster with Pfizer: this is the possible fate towards which a million young people in Italy have received the English vaccine considered dangerous for the health of the under 30s, especially women. While the Regions are proceeding in no particular order – Sicily has decided to suspend the drug for young people – the new line of Cts is to recommend the administration of AstraZeneca to people over 60.
Thus the mix-and-match option, ie mixing a viral vector vaccine (AstraZeneca) with an mRNA one (Pfizer), returns to the center of the debate. The European Medicines Agency EMA has not yet pronounced itself on the matter, the results of the tests conducted so far are reassuring: boostering with a different vaccine should not cause safety or efficacy problems, on the contrary, it would give better results than using a single vaccine. It could also benefit the vaccination campaign because states would have more flexibility in the supply of doses.
AstraZeneca vaccine, second dose with Pfizer is it possible?
In the absence of clear scientific results, theWHO suggests caution in mixing two different anti-Covid vaccines, but countries are moving in no particular order.
In Italy for the moment who receives the first dose of AstraZeneca and awaits the second, to be administered preferably within 12 weeks, will come always vaccinated with AstraZeneca. As clarified in the Q&A ofAIFA (Italian Medicines Agency):
There are still no data on the interchangeability between different vaccines, so those who undergo vaccination of the first dose with the Vaxzevria vaccine will continue to use the same vaccine for the second dose as well.
In an interview with Everyday occurrence Professor Sergio Abrignani, immunologist and member of the Scientific Technical Committee (Cts) said that use two different vaccines in humans, one with a viral vector and one based on DNA, does not involve risks, indeed it is immunologically much higher and it makes sense. “Clinically, we don’t expect any side effects. WHO has suggested caution, not because it expects more risks, but because the rule in the Western world is that there should be a controlled clinical trial. It is currently underway in England, the data will arrive in June. From a formal / regulatory point of view it could not be done, but Germany and France did it because they have national regulatory agencies ”.
The Germany and the France they gave theok to recall with Moderna or Pfizer for those under 55 who received AstraZeneca, and theAustralia doubled his Pfizer orders and changed his vaccination strategy, recommending Pfizer serum to those under 50.
“It wouldn’t be the first time trying to mix two vaccines. This approach is already used to vaccinate against pneumococcus, a bacterial infection caused by the Streptococcus pneumoniae which can lead to pneumonia and meningitis “said Dr. Dana Mazo, an epidemiologist at Monte Sinai Hospital in New York.
In the case of vaccines for Covid, it is necessary to understand what effect the mix between AstraZeneca, which uses vector technology adenovirus, and Pfizer and Moderna that are mRNA vaccines. Both contain instructions that tell our cells to make the SARS-CoV-2 virus spike protein and cause the body to develop an immune response that protects us from exposure to the virus. But the difference is in how these vaccines carry information.
Therefore, mixing the AstraZeneca vaccine with Pfizer or Moderna vaccine would be a novel approach that requires extensive studies.
Vaccine mix: test results
Between delays and inconveniences in the distribution of Covid vaccines and the possibility of having to do another booster of the vaccine in the fall, mix vaccines several could become inevitable. But what do scientists say about the safety and efficacy of this approach? Several researches are underway to understand this.
In the UK the UK health system and the University of Oxford are leading one clinical trial to see if it is safe to mix types of Covid vaccine after the British government has given doctors permission to do first and second doses with two different sera. The first results of the mix and match studies promote it: the combinations of Pfizer and AstraZeneca have boosted immunity of patients.
Another research published on medRxiv, yet to be peer-reviewed, compared the immune responses of 26 individuals between the ages of 25 and 46 who were given one dose of AstraZeneca followed by one dose of Pfizer with those who received two doses of Pfizer. The results showed that the first have developed 4 times more neutralizing antibodies against the English variant two weeks after the recall; levels of neutralizing antibodies to the South African variant were lower than those to the English variant and similar levels to the Indian variant, but in any case higher than the antibodies developed with two doses of Pfizer vaccine.
More studies are needed, but the results of the tests conducted so far are encouraging. “The only caveat are the potential side effects, since one study showed an increase in adverse reactions following the administration of two different vaccines “ said Professor Deenan Pillay, prof. of virology at University College London.
What happens if I miss the AstraZeneca recall?
Skipping the second dose can reduce the effectiveness and potentially the duration of immunity. In fact, in vaccinated subjects who received the second dose after 12 weeks from the first, the effectiveness after 14 days from the injection was82,4%.
Furthermore, according to a study conducted by Princeton University published in Science delaying the second dose of the vaccine can be dangerous in the long term as imperfect immunity can increase the risk of new viral variants and new waves of infections.
The case of those who develop SARS-CoV-2 infection after the first dose of vaccine is different: the ministerial guidelines clarify that they must not receive the second dose and will be taken in charge for the management of the recall.