Combining and spacing AstraZeneca and Pfizer vaccines boosts immune response

Two new studies offer guarantees for greater flexibility in vaccination campaigns against the coronavirus.

A health worker vaccinates a man in one of the centers for the campaign against Covid.

A combined vaccination schedule with a first dose from AstraZeneca and a second, four weeks later, from Pfizer-BioNTech, produces a better immune response than giving a second dose of AstraZenecaaccording to the Com-COV study being carried out by the University of Oxford.

These data support the decision made by some European countries –including Spain– to offer alternatives to a second dose of AstraZeneca after this vaccine has been associated with very rare cases of blood clots.

Matthew Snape, an Oxford professor and one of the study’s lead authors, has pointed out that these findings can be used to give greater flexibility to vaccination campaignsbut the study is not large enough to recommend a change in the approved guidelines.

“It’s really encouraging that these antibody and T cell responses are looking good with a combination of regimens,” he said. The greatest antibody response has been seen in people who have received both doses of the Pfizer vaccine.. The combined regimen with one dose of AstraZeneca and then another of Pfizer produced the greatest T-cell response and also a greater antibody response than the opposite combination, first Pfizer and then AstraZeneca.

The study will also evaluate the results of spacing the doses 12 weeks apart, something that has been seen, in the case of the two doses of AstraZeneca, to produce a greater immune response in this type of vaccine.

Increased immunity with 10 months between doses

These data have coincided in time with a preliminary study published in the medical journal The Lancet which indicates that a third dose of the Oxford and AstraZeneca vaccine against Covid-19 generates a “strong” immune reinforcement against the coronavirus and its new variants.

The initial results of this research, published as a pre-print (that is, not yet subject to external review by other experts), also reflect that delaying the second dose for more weeks may be beneficial in the case of the AstraZeneca vaccine.

The study, developed by the University of Oxford, points out that when the interval between the first two doses is 45 weeks –about ten months–, antibody levels are up to four times higher than with an intermediate period of 12 weeks.

“This is one reassuring news for countries with a lower supply of the vaccinewho may be concerned about delays in providing second doses to their populations,” Andrew Pollard, director of Oxford vaccine trials, said in a statement.

According to the research, antibody levels remain elevated from baseline for at least a year after a single dose, indicating a “robust and long-lasting” immune response, said Mene Pangalos, a director at AstraZeneca.

In addition, the study indicates that giving a third dose at least half a year later would increase antibodies sixfold and it would offer greater immunity against alpha (first detected in the UK), beta (in South Africa) and delta (in India) variants.

However, the study authors note that “it is not yet known whether booster injections will be needed,” either in response to decreased immunity or to boost protection against risk variants.

Regarding the adverse effects of the Oxford and AstraZeneca vaccine, the preliminary results of the research indicate that “they are well tolerated”, with a lower incidence after the second and third doses than after the first.

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