Reaction to the study analyzing the combination of AstraZeneca, Pfizer and Moderna vaccines in Sweden.
Reaction to the study analyzing the combination of AstraZeneca, Pfizer and Moderna vaccines in Sweden.
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A study conducted in Sweden with more than 700,000 people analyzed the effectiveness of the heterologous schedule, consisting of combining the AstraZeneca vaccine with another dose of a messenger RNA vaccine, with the traditional homologous schedule, consisting of two doses of AstraZeneca. The results showed greater protection against SARS-CoV-2 infection when two different vaccines were combined.
A study conducted in Sweden with more than 700,000 people analyzed the effectiveness of the heterologous schedule, consisting of combining the AstraZeneca vaccine with another dose of a messenger RNA vaccine, with the traditional homologous schedule, consisting of two doses of AstraZeneca. The results showed greater protection against SARS-CoV-2 infection when two different vaccines were combined.
Publication
Effectiveness of heterologous ChAdOx1 nCoV-19 and mRNA prime-boost vaccination against symptomatic Covid-19 infection in Sweden: A nationwide cohort study
Not peer-reviewed
Peer-reviewed
What our experts say
Context and background
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Expert Comments:
José Alcamí
The scientific evidence is abundantly clear to say that heterologous guidelines are much more immunogenic, safe and, by this first study, that they have better efficacy in preventing some symptoms.
All studies show that the heterologous combination induces many more high quality antibodies, called neutralizing antibodies, compared to the homologous, and that this regimen is safe. The Lancet Regional Health - Europe article does a first study in the Swedish population to see if this strategy also protects better and they see that it does.
They give efficacies against infection for the homologous AstraZeneca double-dose combination of 50%. For the AstraZeneca-Pfizer combination, 67%. For the AstraZeneca-Moderna combination, 79%. This is consistent with what we know, that Moderna is slightly more potent than Pfizer.
The heterologous combination is significantly better than the AstraZeneca two-dose counterpart. They do it in a population of over half a million people, so it's robust.
The homologous group that received AstraZeneca twice has a higher average age, 67 years, versus 44 years in the heterologous group. I was concerned that there might be some bias, but when they analyze by confounding factors and covariance studies they see that the heterologous guidelines protect younger and older people equally, but that the homologous protects older people worse than younger people. I think this is a very important piece of data that confirms that the homologous combination works less well in older people.
The message that the homologous guideline is less effective needs to be modulated: all combinations protect dramatically against hospitalization. They observe cases of mild symptoms, but the number of patients admitted is very low, a couple of patients per group. When we say it protects less, we are referring to mild or moderate symptoms. Both the homologous and heterologous regimens are highly protective against hospitalization and death.
The study is done in the delta era and this shows that, although in the laboratory we see that the variant is blocked a little worse by the antibodies, in practice it does not change significantly when it comes to avoiding severe cases.
These data support policies that encourage heterologous vaccination.
