AstraZeneca Vaccine Followed by Pfizer Dose Safe: Spain Study

After administration of the Pfizer dose, the presence of neutralising antibodies rose sevenfold.

A study in Spain has found that those under 60 years of age who have already received one shot of AstraZeneca vaccine can be safely administered the Pfizer-BioNTech jab.

(Photo: iStock)

Can COVID vaccines be mixed and matched? How safe are they? A study in Spain has found that, those under 60 years of age who have already received one shot of AstraZeneca vaccine can be safely administered the Pfizer-BioNTech jab, according to Hindustan Times.

The recommendation comes after Spain suspended the use of AstraZeneca vaccine due to concerns of rare blood clots.

Researchers from Spain’s CARLOS III Health Institute in the government-led Combivacs study, found that the presence of IgG antibodies in the bloodstream was between 30 and 40 times higher in people who got the second Pfizer shot than in a control group who only received one AstraZeneca dose.

Meanwhile, after a Pfizer dose, the presence of neutralising antibodies rose sevenfold, which was much higher than the doubling effect observed after a second AstraZeneca shot, Hindustan Times reported.

No Serious Side Effects

Around 670 volunteers aged between 18-59 took part in the study. The participants had received their first dose of AstraZeneca vaccine, with about 450 people receiving the Pfizer vaccine for their second dose. Five major hospitals across Spain are involved in the study.

1.7 percent of the volunteers reported severe side effects, which were limited to headaches, muscle pain, and general malaise, said one of researchers, Dr Magdalena Campins.

"These are not symptoms that can be considered serious," she said.

The recommendation will affect about 1.5 million Spaniards who received the AstraZeneca shot before the government halted it for those aged above 60 years of age due to blood clot concerns, causing widespread uncertainty, according to Economic Times.

Clinical director at Carlos III, Antonio Frias, said the results support the possibility of vaccinating patients who have received the first dose of AstraZeneca, adding that, the "decision is not up to the investigators of this study".

Meanwhile, in a similar "mix-and-match" study in the UK, preliminary findings recently showed that those given a shot of Pfizer followed by a dose of AstraZeneca, or vice-versa, were more likely to report mild or moderate symptoms such as headaches or chills than if they received two of the same type. The data on immune responses are expected in the coming months.

(With inputs from Hindustan Times and Economic Times.)

(The article was first published in FIT and has been republished with permission.)