Updated Covid-19 boosters roughly halve a person’s risk of becoming ill with the coronavirus, even from infections caused by the fast-spreading XBB.1.5 subvariant.
New studies, led by researchers at the US Centers for Disease Control and Prevention, are among the first looks at how bivalent boosters have continued to work in the real world as the world has evolved. virus. The data shows that the boosters continue to offer substantial protection against the variants currently in circulation.
The near real-time data was collected by the federally funded Increased Community Access to Testing program, which administers Covid-19 tests through pharmacies. It includes results for adults receiving tests at participating pharmacies from December 1 to January 13.
Of nearly 30,000 test results included in the analysis, more than 13,000 (47%) tested positive for Covid-19.
More people who tested negative had received an updated bivalent booster compared to those who tested positive.
On average, people in the study who had not received a bivalent booster had also not received a dose of Covid-19 vaccine for over a year. That’s about the same as the national average, according to the study’s authors. Their protection against disease was likely very minimal, they said.
The study results show that updated reminders are more effective for young adults.
For adults aged 18 to 49, boosters reduce the risk of contracting a symptomatic infection caused by the BA.5 subvariant by 52% and the risk of contracting an infection caused by XBB or XBB.1.5 by 49%. . For adults aged 50 to 64, the new reminders reduce the risk of getting sick with Covid-19 by 43% for BA.5 and 40% for the XBB subvariants. For people 65 and older, boosters reduce the risk of infection with symptoms by 37% and 43% for the BA.5 and XBB subvariants, respectively.
Ruth Link-Gelles, CDC senior epidemiologist and lead author of the study, said at a press conference Wednesday that these vaccine effectiveness numbers are averages. Because everyone is unique in terms of underlying health, past exposure to the virus, and other factors, these estimates of vaccine effectiveness may not apply at the individual level. She said it’s important to think about them at the population level.
For people wondering if the bivalent booster protection they got in September has already worn off, it’s too early to tell how the decline would work with these new two-strain vaccines, Link-Gelles said.
So far, there is little evidence of waning effectiveness two to three months after people get vaccinated.
“It is too early, I think, to know how the decline will occur with the bivalent vaccine. We know from older vaccines that protection wanes over time, especially against symptomatic infections. Just like with blanket protection, what we’ve seen in the past is that your protection lasts longer for more severe illness,” Link-Gelles said.
Researchers haven’t had data for three months, she said, but based on experience, she would expect protection against serious illness and death to be higher and last longer than these results against infections.
“We will continue to monitor it over time in the months to come,” she said.
The study authors said these were only estimates of the ability of vaccines to protect people against an infection that causes symptoms such as cough or fever. They probably work even better against more severe outcomes like hospitalization and death.
“What we know from past experience is that vaccines generally protect better against more serious diseases. So these are estimates of symptomatic infection and we would expect similar estimates of hospitalization and death to be higher,” Link-Gelles said.
Asked about the effectiveness of two-strain vaccines compared to older one-strain vaccines, Link-Gelles said it was impossible to know.
“We can’t in the United States make a direct, direct comparison of monovalent and bivalent vaccines because they were never licensed at the same time,” she said. Since protection declines over time, you need to compare groups of people who received each type of vaccine at the same time.
“What this tells us is that people who had the bivalent vaccine were better protected than people who were up to date before, had all their monovalent doses, and had not received the bivalent vaccine,” Link-said Geles.
The CDC said it was able to analyze the data and release it so quickly through the use of a shortcut. Rather than sequence the genomes of each positive result, the researchers relied on a different marker to distinguish the variants.
The tests used in the study rely on a series of probes, or markers, to identify a positive case. Some variants of the virus that causes Covid-19 have mutations in their spike protein that cause one of the test markers to fail. This is called S gene target failure.
In the study, test results that showed S gene target failure were considered an infection caused by a BA.5 subvariant. Those that were positive for the S gene target were considered to be caused by the XBB or XBB.1.5 subline.
As the study continued, XBB.1.5 became a bigger player in the mix of variants.
“Later in the study period, most would be XBB.1.5,” said CDC epidemiologist Heather Scobie.
This gave the researchers confidence that the vaccine effectiveness results reflect how well the vaccines currently work.