The White House says Americans should start getting boosters of Pfizer and Moderna as of September 20.
But leading experts who regulate vaccinations in the US worry we don't yet have evidence to support that move.
Some experts say waiting even longer for boosters could be more effective.
The Biden Administration has announced that, starting on September 20, third doses of Pfizer and Moderna's COVID-19 vaccines should start to become available to Americans who were the first in line to receive their initial two-shot vaccines.
But federal experts who are working behind the scenes on vaccine regulation and safety are still clamoring for more evidence that those third doses are really needed at this juncture for everyone.
"If we're going to move in this direction, I want to see the data," registered nurse Lynn Bahta, who serves on the Centers for Disease Control and Prevention's independent advisory committee on vaccines, said during a meeting earlier this week.
The timing of booster shots matters to our collective immunity against COVID-19, and it's not clear yet to many top experts, including those working inside the CDC and FDA, that most people (aside from the elderly or immunocompromised) need a third COVID-19 shot at eight months post-vaccination.
On Friday, the New York Times reported that the heads of both the CDC and FDA are now urging the White House to walk back its booster recommendation.
Their warnings echo the panel of independent advisors to the CDC, who met earlier this week and raised concerns about rolling out boosters before we have the data for it - risking "over-vaccination."
The White House announced boosters for all - but the FDA and CDC are not on board yet
The Biden Administration's rapid-fire booster shot announcement is still technically pending FDA approval, because the US Food and Drug Administration is the arm of the federal government that approves vaccines and drugs for use.
The Centers for Disease Control and Prevention, and their independent advisors, have a say afterwards in how those vaccines should be used and recommended by doctors and patients nationwide.
According to the Times, both Janet Woodcock, who heads the FDA, and Rochelle Walensky, in charge at the CDC, are asking the White House to scale back its broad booster plan.
Two top officials at the FDA have resigned over the bullish, better-safe-than-sorry White House stance on boosters, seeing it as getting ahead of the science, Politico and Endpoints reported on Tuesday.
Over at the CDC, the independent group of experts tasked with determining what recommendations to put in place for approved and authorized vaccines (called ACIP) is also asking for more compelling data from the government.
"When we discuss this issue of boosters, we have to remember that we're starting at a point that the data to date doesn't show a remarkable reduction in the effectiveness of the vaccines in terms of preventing hospitalizations and deaths," Dr. Beth Bell, a voting ACIP member, said during their meeting earlier this week.
"Really the most important thing that we can do, with respect to vaccines, is to continue to work as hard as we possibly can to encourage more people to get the primary series."
Experts generally agree boosters are needed for some people
Already, booster doses are recommended in the US for immunocompromised patients, who may not receive the usual benefits of a vaccination with just two doses, because of their immune status.
The other important group to boost at this time is the elderly population, especially those living in congregate settings like nursing homes.
Experts agree that those folks don't typically have a very robust or long-lasting immune response to vaccines, and should be prioritized for boosters as soon as possible.
The argument against boosting too soon
Already, millions of other Americans have rolled up their sleeves for third doses though, as the Delta variant continues racing around the US.
"Many people didn't read the fine print," ACIP member Dr. Helen Talbot said, referencing the fact that the booster decision from the White House is not an official one yet. "Since the South is having a horrible outbreak of Delta, many, many, many hospitals have already started vaccinating healthcare workers with third doses, and patients."
There is some emerging evidence to support boosters. On Thursday, Dr. Anthony Fauci, President Biden's chief medical advisor, presented two new studies from Israel which show a reduced risk of infection and severe disease in patients who've gotten a third shot of Pfizer's vaccine.
Fauci said he felt the data supported the White House's booster plan, adding: "I must say from my own experience as a immunologist, I would not at all be surprised that the adequate full regimen for vaccination will likely be three doses."
But the timing of booster shots matters, immunologically speaking. Rushing to get one now may not be the best idea.
Boost too soon, and you don't ramp up protection in any meaningful way, in part because the body hasn't had enough time to build up a proper immune memory of that first vaccination yet.
"It's not detrimental, it's just not necessarily as effective as a later boost," Cameron Wolfe, an infectious diseases expert from Duke, told reporters during a question-and-answer session Wednesday, explaining the dilemma. "Sometimes waiting a little bit extra time is in fact appropriate to gain the strongest response."
'The concern is over-vaccination'
Dr. Jason Goldman, a non-voting member of the advisory committee, agreed that it's probably too soon for most people in the country to be considering getting more shots, especially since the shots likely come with more side effects, like the first and second doses did, and could mean more missed work and bed rest.
"The concern is over-vaccination of patients," he said, who are "going out and getting themselves a third dose" ahead of recommendations.
It's not reasonable to expect any vaccine to prevent every single mild case of infection, especially in the middle of a pandemic, when new variants continue sprouting up to challenge vaccine effectiveness.
For now, vaccines are holding up very well at preventing severe illnesses and deaths, at least for those who've chosen to have them.
"We are still trying to get first doses into healthcare workers who remain reluctant," Dr. Marci Drees, a non-voting member of ACIP added. "If we then say that they also need to get a third dose - that's not totally evidence-based. That can potentially make them even more reluctant."
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