Last week, the CDC published initial data with promising implications for people who get the updated Covid-19 boosters.
Scientists designed the updated, bivalent mRNA boosters to combat the omicron variant, which first reached the United States in November 2021. Omicron had several mutations to the virus’ spike protein, which made it harder for antibodies elicited by the original vaccine to recognize and neutralize. So scientists at Pfizer and Moderna developed boosters designed to combat two omicron subvariants, BA.4 and BA.5.
However, the subvariants kept coming; a variant called BA.2 spawned sublineages XBB and XBB.1.5, each with its own mutations. XBB.1.5 now accounts for nearly 50 percent of new Covid-19 cases in the United States. How well the updated booster would work against XBB and XBB.1.5 wasn’t initially clear.
The CDC’s report offers some reassuring data. Assessing data collected between December 1st, 2022, and January 13th, 2023, researchers say that, for people who have received at least two doses of the initial vaccine, the updated boosters provide additional protection against symptomatic infection for at least the first three months after receiving the booster.
Specifically, in adults 18 to 49, the bivalent boosters were 48 percent effective at preventing symptomatic disease in the first three months following the shot. In people aged 50 to 64, the updated vaccine was 40 percent effective at preventing symptomatic infection in the same period and 43 percent in adults 65 years of age and older.
The slight uptick in efficacy for the oldest group when compared to the 50 to 64 group — which is the opposite of what you’d typically expect to see — may have to do with how researchers collected the data, Krutika Kuppalli, Chair of the Global Health Committee at the Infectious Diseases Society of America, tells Inverse.
“As the study says, one of the limitations is that medical conditions are self-reported, and so is the history of prior infection. Without knowing this information, it is hard to know what to make of the data.”
While the CDC’s report didn’t explicitly look at how well the bivalent vaccines prevented severe illness, two New England Journal of Medicine reports suggest it does.
“It appears that the bivalent boosters provide significant protection against severe omicron in people that have been previously vaccinated or boosted and that the effectiveness wanes over time,” she says. “The bivalent boosters are more effective than the monovalent booster.”
The biggest takeaway from the CDC’s report, especially when taken in context with similarly positive studies evaluating bivalent boosters and severe disease, “is that you need to stay up on your boosters,” Donald Alcendor, an adjunct associate professor of Pathology, Microbiology, and Immunology at Vanderbilt University School of Medicine, tells Inverse.
Unfortunately, booster uptake has been remarkably low compared to the primary vaccine series. Only 15.3 percent of the adult population in the United States have gotten the updated booster. Alcendor thinks this may be for several reasons, all of which could fall under the category of “vaccine fatigue.”
“People don’t understand why we’re recommending Covid-19 vaccine after Covid-19 vaccine,” he says. “Some people think if immunity wanes over a few months, it’s not worth it, or if it only protects against severe disease but not an infection, it’s not worth it.”
But those people would be mistaken, Alcendor says. “Nothing is perfect. And some level of protection may well be enough to keep you out of the hospital or from dying or developing Long Covid; it is worth it.”
When scientists measure waning immunity, they typically look at antibodies in the blood, which doesn’t paint the complete picture. According to a story in The Atlantic, when the quantity of antibodies decreases, it can mean they are “continuing to replace themselves with new versions that keep improving their ability to bring the virus to heel.” In other words, when it comes to fighting infections, the quality of antibodies may matter more than the quantity. Additionally, the immune system also consists of more than just antibody-creating B-cells. T-cells play “a role in long-term immunity to the virus,” according to the National Insititute of Health.
The bottom line, Kuppalli says, “is that vaccination protects against hospitalization and death. So I encourage people who have not had their primary vaccination series to please get vaccinated and, if you have had your primary series, to get your booster.”
