Faced with slow vaccine rollout, scientists consider new tactics

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Washington (AFP)

Should Covid-19 boosters be delayed? Could dose levels be halved and would mixing and matching plans made by different manufacturers work just as well?

These are questions governments around the world are now facing as vaccine rollout falters and the coronavirus continues to rage, spurred by new variants seen as more contagious.

British health officials are setting the tone, announcing they will stretch the second dose of vaccines allowed for use there to three months, well beyond the recommended three or four weeks.

The idea is to increase the number of people who can be reached quickly, even if the level of personal protection is below what is achieved with the booster.

Authorities in England have also granted permission to give people a second injection from another vaccine maker if the type of vaccine obtained the first time runs out.

The United States, meanwhile, has taken a more cautious line.

On Monday evening, Food and Drug Administration chief Stephen Hahn said that while these are “reasonable questions to consider and assess,” the measures are “premature and not firmly grounded in the available evidence. “.

Without it, “we run a significant risk of putting public health at risk, undermining historic vaccination efforts to protect people from COVID-19.”

The division exposes a division among experts, with respected scientists falling on opposite sides of the argument.

Ideally, policy decisions should be based solely on the parameters within which clinical trials have been conducted. But with the virus threatening to spiral out of control, some argue that we are far from an ideal situation.

“We didn’t choose three weeks for Pfizer or four weeks for Moderna because we knew it was perfect,” Howard Forman, a public health expert at Yale University, told AFP.

“It was the best estimate of the optimal time for the booster dose to be given to increase immunity. ”

Forman added that much of medicine is based on imperfect data – such as how long a drug treatment needs to be taken, and doctors routinely prescribe drugs approved for a purpose for other conditions.

“Such modest changes from what we have already recommended can make all the difference in getting better performance from the vaccines we have,” he added.

Forman stressed that he only suggested delaying the second dose – considered essential to ensure long-term protection – and only in the case of those under 65 and those who are less medically vulnerable.

– Slow deployment –

The debate comes amid unexpected delays in the rollout of Covid-19 vaccines.

The United States had set 20 million people as a target for December, but as of January 4, it had only reached 4.5 million.

The US and UK have covered around 1.4% of their population, Europe is far behind, while Israel leads with around 13%.

The Pfizer and Moderna vaccines, based on mRNA technology, achieve about 95% efficacy at the second dose, which is reserved for storage for one person after the first.

The Moderna vaccine in particular showed high levels of protection after the first injection – in the region of 90 percent – but the numbers should be treated with caution as the sample size is small.

Saad Omer, vaccine researcher and director of the Yale Institute for Global Health, told AFP he only sees the need to change tactics in countries where the supply itself is insufficient.

As it stands in the United States, the pace at which vaccines are being sent to the states is only slightly behind schedule, and Omer believes priority should be given to removing the bottleneck in their administration. to people.

As for the vaccine mix, Yale immunologist Akiko Iwasaki said it should work in theory, but experts are unanimous that it requires more study and should only be a last resort for now.

– Confused for the public –

Omer and Natalie Dean, a biostatistician at the University of Florida, argue that the way forward may lie in further analysis of the data to find biological markers, such as antibody levels, that correspond to protection against Covid- 19.

This could be determined by combing through the results of several trials to calculate a cutoff value, and then setting up small studies to find out what dose of vaccine gets you there.

The advantage of this approach is that it would eliminate the need to repeat tests lasting several months.

This could be a promising avenue to pursue for injecting half-doses of the Moderna vaccine, which the data shows could offer the same level of protection, Dean said.

She added that she was concerned the discussion of the changes could confuse the public, “and I am concerned about anything that could compromise trust.”

So people should be assured that any changes in the United States would go through the same transparent regulatory process that granted vaccines their emergency clearance, she said.

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