Should COVID-19 boosters be delayed? Could the dose levels be reduced, and would mixing and matching shots from different makers work just as well?
These are questions now facing governments around the world as vaccine rollouts falter and the pandemic continues to rage, spurred on by new variants that are believed to be more contagious.
British health officials set the pace, announcing that they would stretch out the second dose of vaccines authorized for use there up to three months, well beyond the three or four weeks recommended.
Photo: Reuters
The idea is to scale up the number of people who can be reached quickly, even if the level of individual protection falls short of what is reached with the booster.
The WHO on Tuesday effectively endorsed the position, saying that the second Pfizer-BioNTech vaccine dose could, in “exceptional circumstances,” be delayed for a few weeks.
English authorities have also granted permission to give people a second shot from a different vaccine maker if the kind they got the first time has run out.
Meanwhile, the US has tacked a more cautious line.
US Food and Drug Administration Commissioner Stephen Hahn on Monday said that while there were “reasonable questions to consider and evaluate,” the British moves were “premature and not rooted solidly in available evidence.”
The debate has exposed a division among experts, with respected scientists falling on both sides.
Ideally, policy decisions should rest solely on the parameters in which clinical trials were conducted, but with the coronavirus threatening to spiral out of control, some argue we are in a far-from-ideal situation.
“We didn’t pick three weeks for Pfizer or four weeks for Moderna because we knew it to be perfect. It was the best guess for an optimal time for the booster dose to be given to augment immunity,” said Howard Forman, a public health expert at Yale University in New Haven, Connecticut.
Forman added that much of medicine is based on imperfect data — such as how long a course of drugs should be taken — and physicians routinely prescribe medicine approved for one purpose for other conditions.
“So modest changes to what we’ve already recommended may make all the difference in getting a lot more bang for the vaccines that we have,” he said.
Forman said that he is only suggesting delaying the second dose — seen as vital to ensuring long-term protection — and only in the case of under-65s and those who are less medically vulnerable.
The US had set vaccinations for 20 million people as its target for last month, but as of Monday it had only reached 4.5 million.
Both the US and UK have covered about 1.4 percent of their populations, the EU is far behind, while Israel is out front, having covered about 13.5 percent.
The Pfizer and Moderna vaccines, based on mRNA technology, reach about 95 percent efficacy on second dose, which is reserved in storage for a person after their first.
The Moderna vaccine in particular has shown high levels of protection after the first shot — in the region of 90 percent — but the numbers should be treated cautiously as the sample size is small.
Saad Omer, a vaccine researcher and director of Yale University’s Institute for Global Health, said that he only saw a need for changing strategy where supply is short.
In the US, the rate at which vaccines are being sent to states is only a little behind schedule, and Omer believes addressing the bottleneck in administering them to people should be given priority.
As for mixing vaccines, Yale University immunologist Akiko Iwasaki has said that it should work in theory, but experts agree that it requires more study and should only be a last resort.
Both Omer and Natalie Dean, a biostatistician at the University of Florida, argue that a path forward might lie in further data analysis to find biological markers, such as antibody levels, that correlate to protection against COVID-19.
This could be determined by combing through the results of existing trials to calculate a threshold value, then setting up small studies to determine what dose of vaccine gets you there.
US National Institutes of Health scientist John Mascola on Tuesday told the New York Times that a study based on that process was underway to determine whether half-doses of the Moderna vaccine delivered equal protection.
Dean said that she was worried that the discussion around changes could be confusing to the public “and I’m concerned about anything that could jeopardize trust.”
People should therefore be assured that any changes would go through the same transparent regulatory process that granted the vaccines their emergency authorization, she said.
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