Mixing AstraZeneca with Pfizer could triple some adverse effects
Mixing AstraZeneca with Pfizer could triple some adverse effects

Preliminary findings from a study released Wednesday in the journal “The Lancet“they point to combine doses of covid-19 vaccines developed by AstraZeneca and Pfizer / BioNTech causes mild and moderate reactions up to three times more frequent than if the standard vaccination schedules are followed, with two injections of the same preparation.

A team led by experts from the British University of Oxford launched an investigation in February this year to investigate the effects of combining two doses of preparations manufactured by different pharmaceutical companies and they saw that this increased the so-called reactogenicity.

This term refers to the common adverse reactions expected from a vaccine, such as a excessive immune response, fever, arm pain at the injection site… Experts found that when an interval of four weeks, applying the “mix” schedules (Pfizer-BionNTech, followed by Oxford-AstraZeneca and Oxford-AstraZeneca, followed by Pfizer-BioNTech) generated more mild or moderate reactions after the second dose that if the standard procedure of not combining vaccines from different manufacturers was followed.

They also reported that any adverse effects from the mixture lasted Little time and clarified that no other safety-related concerns were detected.

As the researchers explain in the article, both vaccine combinations (first AstraZeneca and then Pfizer / BioNTech, or vice versa) “induced greater systemic reactogenicity after the booster dose than their counterparts” (second dose with the same vaccine) . Specifically, a 34% (37 of 110) of the participants who received the first dose of AstraZeneca and the second from Pfizer (combination that is also being studied in Spain) had fever, an adverse effect that only 10% of the 112 participants who received the two doses of AstraZeneca reported. In addition, the 41% of the 114 patients analyzed with the first dose of Pfizer and second dose of AstraZeneca reported having a fever, compared to 21% of the 112 recipients of the Pfizer vaccine for both doses. “Similar increases” have been observed in adverse effects such as chills, fatigue, headache, joint pain, malaise, and muscle pain (See table).

Results of the study published in The Lancet on the adverse effects of combining Pfizer and AstraZeneca.
Results of the study published in The Lancet on the adverse effects of combining Pfizer and AstraZeneca.

However, the authors state that in no case were hospitalizations reported for the symptoms of the combination of vaccines, and that most of this increase in reactogenicity was observed in the 48 hours after immunization.

Alert for possible casualties after the vaccine

“Although this is a secondary part of what we are trying to explore through these studies, it is important that we inform people about these data, especially since several countries are considering using these mixed dose schedules, “says Matthew Snape, associate professor of pediatrics and vaccines at the University of Oxford, and lead investigator of the aforementioned trial.

The study findings suggest that “mixed dose schedules could result in a increase in sick leave the day after immunizationIt is important to consider when planning the immunization of healthcare workers, “notes Snape.

Information on the immune response, in June

“Importantly, there are no safety-related concerns,” said the expert, noting that the study does not determine if the immune response “will be affected”. Snape also noted that the research team is confident to report that data “in the coming months.” According to the own study, the researchers anticipate having the information on the immune response generated by combining these two vaccines in June 2021.

The research team informed participating patients that paracetamol could alleviate adverse effects after administration of the vaccines. “Participants were informed that acetaminophen might reduce the side effects of the vaccine, but were not actively advised that they medicate prophylactically “, reads the work.” We have adapted the study to evaluate if the early and regular use of paracetamol reduces the frequency of these reactions “, revealed Snape.

Warning to those under 50 years of age

The data in this study have been extracted from tests carried out in 830 participants over 50 years. The researchers have warned that there is a possibility that the reactions observed in this study “may be more prevalent in younger age groups”, and mentions those who recommend a mixed vaccination program in countries such as Germany, France, Sweden, Norway and Denmark, where vaccines are already being combined in people with the first dose of AstraZeneca – or have omitted the Oxford vaccine – after the serious but very rare thrombotic events combined with thrombocytopenia after the first dose of AstraZeneca.

Decision in Spain, for next week

In Spain there are about 1.7 million people children under 60 years of age who, being essential workers, were vaccinated with the first dose of AstraZeneca before the criterion was changed and this serum was restricted only to those over 60 years of age to “maximize the benefits” of this vaccine that in very rare cases causes rare thrombosis.

A health worker loads a dose of a Covid vaccine in a syringe.

This Wednesday, the Minister of Health, Carolina Darias, reported that the Public Health Commission will take next week “the most appropriate decision“on how those under 60 who received a first dose of AstraZeneca will end up being immunized, if with a second injection from this brand or from Pfizer.

By then, the directors of Public Health of the communities and the Ministry of Health will have at their disposal the “observational studies” of countries that have directly applied a second dose of Pfizer and the clinical trials that are available, as the minister advanced in the press conference after the Interterritorial Council of the National Health System.

One of them is CombiVacs, promoted by the Carlos III Health Institute, which has had the participation of 600 volunteers, of which 400 are part of the intervention group who have already been punctured by Cominarty (Pfizer). Its preliminary results were expected in the presentation of the study “in mid-May.”


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