Slow rollout of Covid-19 vaccines lead scientists to explore precise dose needed for immunity

The US and UK have vaccinated around 1.4 percent of their populations – the highest after Israel, which has vaccinated 12 percent of its population already.

Agence France-Presse January 06, 2021 10:56:28 IST
Slow rollout of Covid-19 vaccines lead scientists to explore precise dose needed for immunity

Adar Poonawalla said that Serum Institute was in the process of signing a larger contract with COVAX for 300 million-400 million doses of the vaccine. That is apart from two existing orders of 100 million doses each for the vaccine developed by Oxford University and AstraZeneca, and another one from Novovax.

Should COVID-19 boosters be delayed? Could the dose levels be reduced by half, and would mixing and matching shots made by different makers work just as well? These are questions now facing governments around the world as vaccine rollout falters and the coronavirus continues to rage, spurred on by new variants that are believed to be more contagious. British health officials are setting the pace, announcing they will stretch out the second dose of vaccines authorised for use there up to three months, well beyond the three or four weeks recommended. 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.

Authorities in England have also granted permission to give people a second shot from a different vaccine maker if the kind the got the first time has run out.

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

On Monday night, Food and Drug Administration chief Stephen Hahn said that while these are "reasonable questions to consider and evaluate", the moves are "premature and not rooted solidly in available evidence." Without this, "we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19 ."

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

Ideally, policy decisions should rest solely on the parameters in which clinical trials were conducted. But with the virus threatening to spiral out of control, some argue we're in far from an ideal situation.

"We didn't pick three weeks for Pfizer or four weeks for Moderna because we knew it to be perfect," Howard Forman, a public health expert at Yale University told AFP. "It was the best guess for an optimal time for the booster dose to be given to augment immunity."

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 added.

Forman stressed that he's only suggesting delaying the second dose – seen as vital to ensuring longer term protection – and only in the case of under-65s and those who are at less medically vulnerable.

Sluggish vaccine rollout

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

The US had set 20 million people as its target for December but as of Jan 4, it had only reached 4.5 million.

Both the US and UK have covered about 1.4 per cent of their populations, Europe is far behind, while Israel is out front having covered some 13 per cent.

The Pfizer and Moderna vaccines, based on mRNA technology, reach about 95 per cent 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 per cent - but the numbers should be treated cautiously as the sample size is small.

Saad Omer, a vaccine researcher and director of Yale's Institute for Global Health, told AFP that he saw only a need for changing tactics in countries where supply itself is short.

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

Confusing to the public

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 multiple trials to calculate a threshold value, then setting up small studies to determine what dose of vaccine gets you there.

The advantage of this approach is it would eliminate the need to repeat months-long trials.

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

She added she was worried that the discussion around changes could be confusing to the public, "and I'm concerned about anything that could jeopardise trust".

People should therefore be assured that any changes in the US would go through the same transparent regulatory process that granted the vaccines their emergency authorisation, she said.

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