- Omicron is continuing to evolve into more contagious subvariants.
- Dr. Peter Marks, who heads the FDA's vaccine division, said the U.S. faces a Covid outbreak this fall as immunity from the vaccines wanes and people spend more time indoors.
- Updating the shots to target omicron could provide more durable protection against the virus, though current supporting data is limited.
The Food and Drug Administration's panel of independent vaccine experts on Tuesday voted 19 to 2 to recommend new Covid-19 shots that target the omicron variant this fall, when public health officials are expecting a new wave of infections.
It is the first time the panel has proposed that vaccine makers modify the shots to target a different variant. The FDA will likely accept the committee's recommendation and authorize a vaccine change. However, the panel did not make a recommendation on which omicron subvariant the shots should target.
Pfizer, Moderna, Novavax and Johnson & Johnson all developed their vaccines against the original Covid strain that first emerged in Wuhan, China, in 2019. But as the virus has rapidly evolved over the course of the pandemic, the vaccines have become less effective at protecting against infection and mild illness, though they are still generally protecting against severe disease.
The vaccines target the spike protein the virus uses to invade human cells. However, the shots have trouble recognizing and attacking the spike the more it mutates away from the original version of the virus. The omicron variant is the most dramatic example yet with more than 30 mutations. That is one of the central reasons why omicron caused such a massive wave of infections last winter despite the fact that masses of people were fully vaccinated.
Fall booster campaign
Omicron continues to mutate into more contagious subvariants. Dr. Peter Marks, who heads the FDA's vaccine division, said the U.S. faces a Covid outbreak this fall and winter as the virus evolves, vaccine immunity wanes and people spend more time indoors where Covid can spread much easier than outdoors.
"For that reason, we have to give serious consideration to a booster campaign this fall to help protect us," Marks told the committee. "The better the match of the vaccine to the circulating strain, we believe may correspond to improved vaccine effectiveness and potentially to a better durability of protection."
Justin Lessler, an epidemiologist at University of North Carolina Chapel Hill, said 95,000 additional people could die in the U.S. from Covid by March 2023 in the most optimistic projections from a team of scientists who are developing models of the pandemic's trajectory. In the most pessimistic scenario, 211,000 people could perish from the virus by March of next year, he said. However, Lessler cautioned that there is a lot of uncertainty in those projections.
Three doses from the current vaccines are just 19% effective at preventing infection from omicron among adults ages 18 and older 150 days or more after administration, according to data presented by the Centers for Disease Control and Prevention. This low protection against infection is likely due to omicron evolving into the more contagious BA.2 and BA.2.12.1 subvariants, CDC official Dr. Ruth Link-Gelles said. A third dose was 55% effective at preventing hospitalization from these subvariants among adults 120 days or more after receiving the shot, according to the data.
Limited data, limited time
The virus is evolving so quickly that the vaccine companies are struggling to keep up. Pfizer and Moderna developed their omicron shots against the original version of the variant, BA.1. However, BA.1 is no longer circulating in the U.S. A more contagious omicron subvariant, BA.2, became dominant over the spring. The omicron subvariants BA.4 and BA.5 are now rapidly gaining ground in the U.S. and are poised to become dominant, Marks said.
Pfizer and Moderna presented data, based on small studies of several hundred people, showing their omicron shots significantly boosted the immune response against omicron BA.1 compared to the original shots that targeted the virus strain that emerged in China. However, the updated shots did not perform as well against BA.4 and BA.5, though the immune response was still strong. There is no available data on the real world effectiveness of the updated shots, though the strength of the immune response is generally viewed as an indication of how much protection the shots will provide against illness.
But Dr. Paul Offit, a committee member, said it's unclear whether the immune response data will translate into significant protection.
"I just think we need a higher standard for protection and than what we're being given — I think it's uncomfortably scant," said Offit, an infectious disease expert at Children's Hospital Philadelphia, about the data presented at the meeting.
The FDA panel members seemed to agree that it would be better to target omicron BA.4 or BA.5. But this could create logistical challenges for the vaccine companies because they have been focused on BA.1. The manufacturing process for a different subvariant would take about three months.
Panel member Dr. Mark Sawyer said the FDA risked falling even further behind the evolution of the virus if it did not act soon.
"Given that state of evolution, we are going to be behind the eight ball if we wait longer," said Sawyer, a professor of pediatrics University of California San Diego.
Novavax presented data showing a booster dose of its current vaccine, which targets the original virus strain, produced a strong immune response against the omicron subvariants. Dr. James Hildreth, a temporary committee member, said he was most impressed by Novavax's data and encouraged the FDA to quickly authorize the shot for use in the U.S. However, FDA official Jerry Weir said the Novavax data hasn't been independently verified by the agency.
Panel member Dr. Cody Meissner said he was worried there isn't enough safety data on how changing the vaccines' composition might impact heart inflammation, or myocarditis, as a side effect. Pfizer and Moderna's current shots have been associated with an elevated risk of myocarditis in adolescent boys.
"We need more study or research into what is the association with vaccines and myocarditis," Meissner said.
Marks said it's crucial to make a decision soon on whether to update the vaccines, so the manufacturers have time to produce the shots in time for the fall. However, Congress has not appropriated money for the U.S. to buy additional vaccines. The White House has warned that without more funding, the U.S. might have to ration shots in the fall for people at highest risk such as the elderly.
Dr. Ashish Jha, who coordinates the U.S. Covid response, has said other countries have already entered negotiations with the vaccine makers for updated shots. The White House has carved out $5 billion in funding to get talks with companies started as the administration waits on more money from Congress. The $5 billion the White House is using for vaccines was originally intended for Covid tests and protective equipment, which means there is now less money for those other crucial tools to fight the pandemic.