People age 65 and older are eligible for another COVID-19 booster shot.
On April 18, the U.S. Food and Drug Administration authorized another round of bivalent booster shots for people in this age group and individuals who are immunocompromised.
Adults age 65 and older who haven’t had a COVID-19 booster shot in four months are eligible. Individuals with a weakened immune system can get a new booster two months after their most recent dose.
“COVID-19 continues to be a very real risk for many people, FDA vaccine chief Dr. Peter Marks told The New York Times. “The available data continue to demonstrate that vaccines prevent the most serious outcomes of COVID-19, which are severe illness, hospitalization and death.”
What are ‘bivalent’ boosters?
The “bivalent” booster shots, introduced in fall of 2022, are designed to protect against the original strain of COVID-19 as well as the now-dominant omicron variant
“It’s basically a 50-50 mix of the omicron variants and the original strain,” says Otto Yang, MD, a professor in the Departments of Medicine and Microbiology, Immunology and Molecular genetics at the David Geffen School of Medicine at UCLA. “The intent is to make the vaccine better matched to the newest circulating strain.”
The omicron variant has about 50 mutations to the spike protein – a protein on the outside of a coronavirus that it uses to enter human cells -- on which the original vaccine was based, Dr. Yang says. These mutations are mostly centered around a part of the spike protein called the receptor binding domain (RBD), which the virus uses to attach to a cell and infect it.
To prevent infection, antibodies need to essentially cover up this RBD to block the virus from attaching to cells.
Antibodies induced by the original COVID-19 vaccines are targeted to the original spike protein, and the changes in omicron reduce the ability of antibodies to attach. Because antibodies play an early role in preventing symptomatic infection, this has allowed “breakthrough infections” in people who are fully vaccinated, Dr. Yang says.
“The new booster is to try to reduce that issue,” he says, “by prompting the immune system to make antibodies against the omicron version of RBD.”
According to the U.S. Centers for Disease Control and Prevention, only about 43% of people age 65 and older have received a bivalent booster shot. Among adults 18 and older, that number is only 20%.
The original vaccines are still providing protection from severe illness and death despite breakthrough infections, however. T-cells generated by the vaccines still mobilize to fight infection, even from omicron.
“T-cells recognize an infected cell through any part of spike,” Dr. Yang says. “So, to a T-cell, the omicron variant is still 97% the same as the original strain.”
The RBD is only a small part of spike, so most T-cells are unaffected by the changes in omicron, he says.
Like antibodies, T-cell responses wane over time, Dr. Yang says: “The protection from T-cells start to drop around four months, increasing the risk of severe illness.”
Scientists hope that the omicron-targeted antibodies from the bivalent boosters will reduce breakthrough infections, he says, thus reducing the circulation of virus in the community.
California is still logging a daily average of 1,376 reported COVID-19 cases and 15 deaths.
