The US this week approved the first major revision of Covid-19 vaccines in a bid to stem an expected spate of infections and hospitalizations this fall.
However, it is unclear how much protection the new booster shots will offer. The Food and Drug Administration and the Centers for Disease Control and Prevention have cleared the footage without data from clinical trials testing the newly formulated doses in humans.
The new boosters, approved for people 12 and older, target the highly contagious and immune-avoidable subvariant omicron BA.5, which sparked a surge in breakthrough infections over the summer. The shots also targeted the original strain of the virus, which first emerged in Wuhan, China, in 2019.
The country’s top health authorities acted urgently this summer to ensure the new boosters are rolled out in time for the fall. They are concerned that the declining effectiveness of legacy vaccines creates an opportunity for omicron to trigger another wave of hospitalizations this winter as people spend more time indoors, where the airborne virus spreads more easily.
According to CDC epidemiologist Heather Scobie, deaths and hospitalizations among the elderly, the most commonly vaccinated age group in America, have risen since April as Omicron continues to mutate into more transmissible subvariants that evade the protection of the original vaccines.
dr Peter Marks, who heads the FDA’s office that reviews vaccines, said the new boosters aim to restore the high level of protection vaccines showed in early 2021. However, Marks acknowledged that federal government experts just don’t know yet whether the boosters will meet the high bar that these doses set.
“We don’t yet know exactly if we’ll reach the same level, but that’s the goal here. And we think the evidence we’ve seen suggests that,” Marks told reporters during a news conference following the FDA approval Wednesday.
The FDA will be monitoring to see if the boosters are meeting that goal, Marks said. When Pfizer and Moderna’s syringes were approved in December 2020, they offered more than 90 percent protection in preventing Covid.
Marks told reporters it will likely be at least a few more months before human data on the BA.5 boosters is available to the public. But he said the FDA used essentially the same process to authorize the new boosters it’s relied on for years to switch virus strains in flu shots.
“We’re pretty confident that what we have is very similar to the situation that we’ve done in the past with influenza mutations where we’re not conducting clinical trials for them in the United States,” Marks said. “We know from how the vaccine works and from the data we have that we can predict how well the vaccine will work.”
The new boosters could prevent 2.4 million infections, 137,000 hospitalizations and 9,700 deaths if no new variant emerges, according to a forecast by a team of scientists predicting the course of the pandemic, called the Covid-19 Scenario Modeling Hub.
However, according to the scientists, this forecast is based on optimistic assumptions about the coverage and effectiveness of boosters. The model assumes that vaccines will prove 80% effective in preventing disease and the public will largely embrace the new boosters. There is no efficacy data on the new shots and it is unclear how strong the public demand for them will be.
The CDC estimates that an early fall immunization campaign with booster shots could save the United States between $63 billion and $109 billion in medical costs by preventing hospitalizations and ICU admissions.
Pfizer and Moderna originally developed new boosters to target the first version of Omicron, BA.1, which caused the massive wave of infections and hospitalizations last winter. But keeping up with the rapid evolution of the virus has proven to be a challenge.
By the time the country’s top health leaders began providing new boosters in earnest in April, more transmissible subvariants had already pushed omicron BA.1 out of circulation. In June, the FDA urged vaccine makers to shift gears and target Omicron BA.5 after it rose to dominance.
That decision didn’t leave Pfizer and Moderna enough time to complete human clinical trials of the new boosters before a fall launch of the vaccine.
As a result, the FDA and CDC rely on human data from the clinical trials of the BA.1 syringes to understand how the BA.5 boosters might work. They also relied on data from studies testing the BA.5 boosters in mice.
The CDC’s Independent Advisory Committee supported the shooting Thursday in an overwhelming vote.
However, some members of the panel also had concerns about the lack of human data.
“I’m really struggling with a vaccine that doesn’t have clinical data that’s reported for people, for those who would actually get the vaccine,” said Dr. Oliver Brooks, a committee member and chief medical officer at Watts HealthCare Corp. in Los Engel.
dr Pablo Sanchez, the only member of the CDC committee who voted against the injections, called the decision to recommend the new boosters without human data premature.
“There’s already a lot of hesitation with vaccines — we need the human data,” said Sanchez, a professor of pediatrics at Ohio State University.
dr Doran Fink, deputy chief of the FDA’s Division of Vaccine Review, told the hesitant committee members that the new booster shots use the exact same manufacturing process as the old vaccines and contain the same total amount of mRNA, the code that instructs human cells to produce the proteins that evoke an immune response to fight off Covid.
Fink said the BA.1 and the BA.5 recordings are similar enough to use data from the BA.1 human trials to get a good idea of how the new BA.5 boosters work will work.
Pfizer and Moderna presented data at the CDC meeting showing that the BA.1 vaccines elicited a stronger immune response in humans than the old vaccines. The mouse studies by both companies on the BA.5 syringes also showed a stronger immune response.
CDC Director Dr. Rochelle Walensky said last week that a longer wait for human data from the BA.5 shots could mean the boosters are out of date by the time a new variant emerges.
“It’s always about too slow versus too fast,” Walensky told Conversations on Health Care in a radio interview. “One of the challenges is when we wait for that data to show up in human data… we’re going to be using what I think might be an outdated vaccine.”
Moderna completed recruitment for its clinical trials last week and expects results by the end of the year. Pfizer’s clinical trials are ongoing, although the company hasn’t given a timeline for when it will have data.
Brooks questioned why the FDA chose a BA.5 vaccine when clinical data is available for the BA.1 vaccines that vaccine manufacturers originally developed. Canada and the UK have approved new booster shots targeting omicron BA.1
Fink said the US approved BA.5 based on advice from the FDA’s independent committee, data from South Africa indicating that natural infection by the subvariant provides broader protection than infection by BA.1, and the fact that BA.5 is dominant.
Although committee members were somewhat reluctant to proceed without the human data, they agreed that the new boosters should have a similar safety profile to the old vaccines, as they use the same platform. The Covid vaccines have been given to millions of people in the US with mostly mild side effects.
According to the FDA, the most common side effects from the human trials of BA.1 syringes were pain, redness, swelling at the injection site, fatigue, headache, muscle pain, joint pain, chills, nausea, vomiting, and fever.
dr Sara Oliver, a CDC official, told the committee that the risk of myocarditis, an inflammation of the heart muscle, after a BA.5 booster is unknown. However, health authorities believe it will be similar to the risk seen with the old vaccines.
The Pfizer and Moderna vaccines have been associated with an increased risk of myocarditis in young men and adolescent boys, mainly after the second dose. However, according to the CDC, the risk of myocarditis is higher from Covid infection than from vaccination.
dr Grace Lee, the chair of the CDC committee, tried to reassure the public that there is a robust monitoring system to monitor safety and that the panel will meet again if new concerns arise.
“I just want to make sure members of the public know we’re continuing to monitor closely,” Lee said. “We have systems and teams that continue to monitor and meet.”
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