Extending the time between Covid jabs: pragmatic or a gamble?

By Guillermo Ximenes

London, Jan 28 (efe-epa).- The decision in the United Kingdom to extend the period between Covid-19 vaccine doses has divided expert opinion as some see it as a pragmatic move to confront the emergency situation while others worry it could be too much of a gamble.

Sir Chris Whitty, the chief medical officer for England, has said the “the great majority of the protection is given by the first vaccine” and that “the second will top that up and extend it over time.”

The British Society for Immunology signaled support for the strategy as a short-term measure given the “unprecedented situation” brought on by the pandemic, although it acknowledged that uncertainties remain given the plan is not based on clinical trials.

The World Health Organization has also warned of a lack of clinical evidence but said that the dosage delay could be stretched to six weeks in exceptional circumstances, a similar timeframe to that recommended by the European Medicines Agency but half of that planned by the UK.

In clinical trials, the second dose of the Pfizer/BioNTech vaccine was administered 21 days after the first while Moderna doses were spaced 28 days apart.

AstraZeneca held various trials and its results found that a gap of two to three months between doses could generate a stronger immune response, although the experts highlighted that such an extended period was only tested on a small group of volunteers.

A study published by the New England Journal of Medicine in December suggested that the Pfizer-BioNTech vaccine had an efficacy rate of 52.4% during the time between doses.

A separate report published by the public health system in England this week said that the majority of those who catch coronavirus after the first vaccine do so during the first 10 days, after which the effectiveness of the inoculation appears to be stronger.

“If there were unlimited resources of both vaccines and vaccinators, there is no doubt it would be better to stick to the trial dosing,” says Stephan Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine.

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