Combining doses of AstraZeneca and Pfizer appears to be beneficial in protecting against COVID-19 and could become an alternative to speed up vaccination.
The idea of combining vaccines against COVID-19 gained momentum as a result of the shortage of doses to complete vaccination schedules around the world. The hoarding of available vaccines by a handful of rich countries and the irregular pace of manufacture by pharmaceutical companies has caused a slowdown – and in some cases, a complete brake – in vaccination campaigns in underdeveloped countries.
Since most of the vaccines developed so far require a couple of injections separated by at least 21 days, some countries speculated with the possibility of covering the second dose with a different vaccine than the first one.
The first country to suggest the combination of vaccines was the United Kingdom in January, which implemented a policy to swap doses of AstraZeneca and Pfizer if any were not available to complete vaccination schedules. Since then, the University of Oxford launched a study called Com-Cov to test the risks and benefits of combining both vaccines.
And although in April 2021 the WHO immunization expert group insisted that there was still no adequate data to determine the safety and efficacy of combining vaccines, the previous results of different studies seem to show that this strategy can promote a powerful immune response. :
The first recently published Com-Cov results focus on reactions after receiving the second dose and have so far concluded that cases of muscle pain, low-grade fever and generalized fatigue can triple compared to those who were vaccinated with the same formula, explains Ignacio López-Goñi, expert professor in microbiology for The Conversation.
However, these effects were mild in all cases (none had to be hospitalized) and most were alleviated with a pain reliever.
At the same time as Com-Cov, a Spanish study with 663 volunteers analyzed the behavior of the immune system of participants who received a first dose of the AstraZeneca vaccine and were subsequently inoculated with the second dose of Pfizer.
So far, the research has yielded two important conclusions: IgG antibodies have risen markedly after receiving the Pfizer dose (more than expected from the original AstraZeneca booster), while there were mild reactions from 24 to 48 hours after receiving the immunization.
In conclusion, both studies have so far only evaluated the mild side effects that appear 24-48 hours after vaccination and the production of neutralizing antibodies. They do not serve to evaluate those possible serious secondary effects that occur with very low frequency ”, concludes López-Goñi.
These previous results suggest that the Pfizer vaccine enhances the immune response of those vaccinated with a first dose of AstraZeneca; however, it’ll be necessary to wait for the progress of both studies so that the strategy of combining vaccines is implemented around the world.