Researchers have been toying with idea of mixing Vaccines against COVID 19 for increasing their efficacy and overcome shortage of Vaccines.
Preliminary results of a spanish study on mixing COVID-19 vaccines have conveyed that giving a dose of Pfizer's drug to people who already received a first shot of AstraZeneca vaccine is highly safe and effective.
The government-led Combivacs study by investigators at Spain's CARLOS III Health Institute has revealed that people who got the second Pfizer shot after a jab of AstraZeneca vaccine had 30 and 40 times higher IgG antibodies compared to control group who only received one AstraZeneca dose.
The researchers engaged around 670 volunteers aged between 18-59 years in five major hospitals across Spain 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.
It was noticed that after administration of the Pfizer dose, the presence of neutralising antibodies rose sevenfold.
Just 1.7 per cent of the participants reported severe side effects, which were limited to headaches, muscle pain and general malaise, said Dr Magdalena Campins, one of the study's leaders.
"These are not symptoms that can be considered serious," she said.
Spain undertook the study to determine how best to proceed after limiting AstraZeneca's shot to people aged over 60 due to concerns about blood clotting in younger people.
In a U.K. "mix-and-match" study, first findings recently showed that people vaccinated with a shot of Pfizer's vaccine followed by a dose of AstraZeneca's, 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. Data on immune responses are expected in the coming months.
That restriction caused widespread uncertainty and meant some younger people who had already received a first dose have been excluded from getting a second.
"Today's results support the possibility of vaccinating patients who have received the first dose from AstraZeneca, but the decision is not up to the investigators of this study," said Jesus Antonio Frias, clinical director at Carlos III.