US officials preparing to roll out Covid-19 booster shots in the face of waning vaccine protection and surging hospitalisations and deaths caused by the highly contagious Delta variant are hoping boosters might prevent mild cases as well.
In theory, that could reduce virus transmission — a goal officials have been less explicit about — and hasten America’s recovery.
“It is not the primary reason (for boosters), but it could actually be a very positive offshoot,” Dr Anthony Fauci, one of the Biden Administration’s Covid-19 advisers and the nation’s top infectious disease doctor said.
The main reason for boosters, Fauci said, is to reverse the trend of rising “breakthrough” infections among people who are fully vaccinated, a point that many experts dispute.
Available data has shown that most severe breakthrough cases have occurred in people over 65 or among those who are immunocompromised. That latter group is already recommended for a third dose.
Dr Larry Corey, a virologist at Seattle’s Fred Hutchinson Cancer Center who is overseeing the US-government backed Covid-19 vaccine trials, is a proponent of using booster doses to bolster antibody levels enough to prevent infection.
“If you don’t get infected, you’re not going to transmit it to others, and we will more effectively abort the epidemic, and that has economic benefits,” Corey said.
The problem there, many experts point out, is that there is scant scientific evidence showing that boosters will in fact prevent infections and transmission.
Some government studies have shown that when infected with the Delta variant, fully vaccinated people can transmit the virus, mostly to unvaccinated people.
“If you take a look at the evidence from the United States, it is very clear that protection against infection and mildly to moderately symptomatic disease is diminishing,” Fauci said.
It is happening among many of the US study populations — including a recent study of 600,000 Covid-19 cases in 13 states and large cities. “Not dramatically, but enough,” he said.
While some 63% of eligible people in the United States are fully vaccinated, the Delta variant has caused a surge in the deadly disease among the unvaccinated.
The two most widely used vaccines in the United States — those based on messenger RNA (mRNA) technology made by Pfizer Inc with BioNTech SE and Moderna Inc — are highly effective but less so against Delta.
Cases are rising among the vaccinated — including some that result in hospitalisation and death.
Debate over booster doses in the United States has become a sore point for virologists, who largely remain unconvinced that the vaccines are losing their ability to prevent severe disease and hospitalisation.
This week, an article in the journal Lancet by two departing FDA vaccine experts and senior scientists at the World Health Organisation, challenged the rationale for booster doses, saying more evidence is needed to justify their widespread use and that most cases of Covid-19 are spread by the unvaccinated.
Dr Paul Offit, an infectious disease expert at the University of Pennsylvania and a member of the FDA’ vaccine advisory panel, is unconvinced by arguments that boosters are needed just yet.
“The question is, what’s the goal? If the goal of the third dose is to enhance protection against serious illness, there’s no evidence that that’s a problem,” Offit said.
If the goal is to increase levels of neutralising antibodies with the aim of decreasing asymptomatic or mild cases, “then we should see those data.” — Reuters
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