Booster shots that target the omicron subvariants responsible for most of the current COVID-19 transmission are expected to become available next week.
The U.S. Food and Drug Administration authorized updated boosters made by Moderna and Pfizer on Wednesday. The bivalent vaccines are designed to better protect against the BA.4 and BA.5 omicron subvariants while also providing protection against the original strain of the virus, which succumbed to variants long ago.
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The U.S. Centers for Disease Control and Prevention and its director, Dr. Rochelle Walensky, must recommend the boosters before they can become available. Once that occurs, the Pfizer and Moderna shots will become available to adults whose last booster came at least two months ago. The Pfizer booster also will be available to children ages 12-17.
Health officials anticipate a surge of infections caused by the omicron subvariants this fall and winter. The BA.5 subvariant has accounted for about 88% of COVID-19 cases in the United States in recent weeks. A new subvariant, BA.6, also has emerged, but it's unclear whether it can out-compete BA.5.
"The COVID-19 vaccines, including boosters, continue to save countless lives and prevent the most serious outcomes (hospitalization and death) of COVID-19," FDA Commissioner Dr. Robert M. Califf said Wednesday. "As we head into fall and begin to spend more time indoors, we strongly encourage anyone who is eligible to consider receiving a booster dose with a bivalent COVID-19 vaccine to provide better protection against currently circulating variants.”
Though many infectious disease experts have praised the quickness of the FDA's efforts to update boosters, others have cautioned about the lack of data from human clinical trials.
The FDA based its decision to authorize the updated boosters on the safety and effectiveness data from the original COVID-19 vaccines, as well as data from an earlier bivalent vaccine candidate that targeted the BA.1 omicron subvariant. The only data submitted on the boosters targeting BA.4 and BA.5 came from nonclinical mouse studies.
However, the FDA said the safety data accrued on Moderna's and Pfizer's original and investigational bivalent vaccines are relevant to the updated boosters because they are manufactured using the same process.
The commonly reported side effects for both boosters remain pain, redness and swelling at the injection site, fatigue, headache, muscle pain, chills, joint pain and fever.
Though many public health officials are hopeful that the updated boosters will help prevent a surge of infections in the fall and winter, some scientists fear the FDA rushed its decision, suggesting officials relied too heavily on data from mouse studies.
Without human data, public health officials will not know how effective the shots are until the fall booster campaign already has begun, some critics say.
"There's no reason to think they'll be unsafe," Dr. Celine Gounder, an infectious disease specialist at NYU Langone Health in New York City, told NBC News. "But whether they'll provide significantly more protection than the original vaccines? Of that I'm skeptical."
Dr. Paul A. Offit, a vaccine expert at the Children's Hospital of Philadelphia, has questioned whether the new boosters will increase protection enough to warrant the switch.
In an op-ed published by STAT before the FDA's decision, he and John P. Moore, a virologist at Weill Cornell Medicine in New York City, urged the FDA against making a hasty decision, arguing that small-scale human clinical trials could be conducted within a few weeks. They wrote:
Moderna and Pfizer executives have claimed that the Omicron vaccines will be protective for longer. That may be true, but how long is longer? A few weeks? A month or two? Again, detailed modeling of the data might provide important information. It’s important to be sure that changing the booster vaccine to include the Omicron sequence offers enough of an advantage to justify the cost and complexity associated with making the switch.
Moore expanded on his opinion in an interview with NPR
"It could be problematic if the public thinks that the new bivalent boosters are a super-strong shield against infection, and hence increased their behavioral risk and exposed themselves to more virus," he said.
Despite these concerns, the FDA's decision also has drawn support among some scientists.
"The FDA is doing the right thing now in the face of winter and evolving variants," Dr. Jeanne Marrazzo, director of the infectious-diseases division at the University of Alabama at Birmingham, told The Washington Post. "Most people who have taken care of patients are freaking out about what might happen in the fall and saying, 'How can you not do something?'"
Many experts also note that annual flu shots are approved in a similar fashion. Animal studies are used to make the yearly adjustments to the vaccine.
Both Moderna and Pfizer plan to conduct human trials on their updated boosters.