New omicron-specific COVID-19 booster shots are rolling out across the country, including at UCLA Health. The U.S. Centers for Disease Control and Prevention recommends that everyone age 12 and older who has been fully vaccinated receive the new booster dose.
“If you are eligible, there is no bad time to get your COVID-19 booster,” says CDC director Rochelle Walensky, MD, MPH, “and I strongly encourage you to receive it.”
This new “bivalent” booster delivers the spike proteins from the original strain of COVID-19 as well as the now-dominant omicron sub-variants BA.4 and BA.5.
“It’s basically a 50-50 mix of the newest 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.”
An expert in cellular immunology who has been studying COVID-19 since the virus emerged, Dr. Yang answers common questions about the new booster:
Why do we need an omicron-specific booster?
The omicron variant has about 50 mutations to the spike protein 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.”
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.
This explains why hospitalization and death rates among vaccinated people have dropped significantly, he says: “They still have good T-cell responses that prevent them from getting severely ill or dying.”
If the T-cells are still effective, why do I need a new booster?
Like antibodies, T-cell responses wane over time, Dr. Yang says: “The protection from T-cells starts to drop around four months, increasing the risk of severe illness.”
Plus, it is hoped that the omicron-targeted antibodies from the new boosters will reduce breakthrough infections, he says, thus reducing the circulation of virus in the community to protect those who remain vulnerable despite vaccines due to weakened immune systems.
Who is eligible for the new booster?
People who are fully vaccinated against COVID-19 and those who have received previous boosters are eligible for the new shot. Two have been authorized. Pfizer’s booster is available for people 12 and older; Moderna’s is authorized for people 18 and older.
The booster is not for people who have yet to receive a primary vaccination series against COVID-19.
When should I get the new booster?
If it has been at least two months since your last booster shot or three months since a COVID-19 infection, you can get the new shot.
Some scientists, however, think two months is too soon.
It would be good to get the booster before the fall-winter flu season, he says.
Can I get the new booster at the same time as the flu shot?
Yes, Dr. Yang says: “There doesn’t seem to be a problem with combining vaccines.”
Why doesn’t vaccine-induced immunity last longer?
“The short-lived protection from the vaccines is not actually a limitation of the vaccine. It has something to do with the limitation of immune responses against this virus,” Dr. Yang says. “To make a vaccine that’s going to give longer immunity is going to have to somehow improve upon nature, because natural immunity after COVID-19 is similarly short-lived.”
If COVID-19 becomes a seasonal coronavirus — and it’s too soon to tell just yet, Dr. Yang says — we may need annual boosters the same way we get annual flu shots. Even though immunity from the vaccine wanes after four months, that could be enough protection to span the infectious season.
Don’t breakthrough infections mean the vaccines aren’t working very well?
Not at all, says Dr. Yang.
“That’s seriously bad misinformation,” he says. “If you look at death rates and hospitalization rates pre-vaccine and post-vaccine, or if you look at hospitalization rates of people who have been vaccinated and people who haven’t been vaccinated even now, it’s quite clear that the vaccines are a major factor in reduced hospitalization and death rates.
“The vaccines are still protecting you. They’re protecting you from the most important thing, which is from dying, even if a breakthrough infection occurs. So it still remains extremely important to get vaccinated.”
Everyone who qualifies to be vaccinated or boosted should do so, he says, “because COVID remains a threat to society in general.”
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