Delaying the second dose, the response to a slow vaccine supply

Faced with a limited supply of vaccines and anxious populations waiting their turn, more and more countries are turning to a strategy that was initially controversial and now justified by scientific studies: doubling or tripling the intervals between the first and the second. second dose of the covid vaccine.

A delay in obtaining the second vaccine not only allows the existing vaccine supply to be distributed more widely, but increases its protective power by giving the immune system more time to respond to the first inoculation. The levels of antibodies produced to fight the virus are between 20% and 300% higher when the follow-up vaccine arrives later., according to new research.

This could be good news for places like Singapore, which is currently facing an unusual, albeit slight, increase in cases after strict mitigation measures contained the virus last year. The city-state is now extending dose intervals, previously from three to four weeks, from six to eight weeks, in order to meet the goal of covering its entire adult population with at least one vaccine by the end of August. India, facing a catastrophic epidemic, recommends 12 to 16 weeks between the first and second dose.

Other countries in similar situations, with low doses of vaccine and restless populations, are likely to follow.

Carla Vizzotti explained what will happen to second doses of Sinopharm, Astrazeneca and Sputnik V

“If I could, I would push a button that says now, now we give everyone we hit a dose,” said Gregory Poland, virologist and director of the Mayo Clinic Vaccine Research Group. “We will move on to the second dose later.”

“In the middle of a burning world, you put out as many fires as possible, as fast as you can,” Poland said.

When the vaccine was released in late 2020, reassuring evidence on longer dosing intervals was not available. Countries then limited its use to those most at risk and guaranteed a second vaccine for those segments. The UK was the first to reject these limitations amid a massive outbreak at the end of 2020, a move initially criticized but which has now proven to be premonitory.