Americans who got their COVID-19 bivalent booster vaccine are not fully protected against getting sick, according to a new report.
The Centers for Disease Control and Prevention released a report that said the updated boosters were just 48% effective at preventing symptomatic infection from the XBB variant of the disease.
The World Health Organization has a 50% threshold to deem a vaccine effective — meaning the bivalent shots fall just below their benchmark when targeting the dominant XBB strain.
However, the CDC noted that the main function of the vaccine is to prevent hospitalization and death, rather than transmission and minor illness from the virus — and the booster is still expected to provide protection against severe sickness.
Indeed, a 2022 study published in the New England Journal of Medicine concluded that if you had been infected with COVID before, that gave you 46.1% effective protection against the omicron variant of the disease — while having a previous infection as well as two doses of a vaccine protected you against infection at 55.1%. Meanwhile, having a previous infection and three doses of a vaccine brought you to 77.3%.
Researchers at the CDC compiled data from a government COVID testing initiative conducted between Dec. 1, 2022, and Jan. 13, 2023 — when XBB and XBB.1.5 were the dominant strains. Symptomatic infection was defined by the person having one or more symptoms.
Researchers determined whether the tested people were vaccinated and compared it to overall population vaccine data, finding that the people who received the booster were 48% more protected than those who did not get it.
Only 15% of the US population has received the bivalent booster, according to the CDC.
The bivalent booster was the fourth or fifth dose of the vaccine for most participants, and it was between 40% and 50% effective for up to three months after receiving it in almost all age groups.
Effectiveness against XBB and its subvariants is just slightly lower than the vaccine’s 52% effectiveness against the BA.5 variant, or omicron.
Some scientists even called the highly mutated variant the most vaccine-resistant strain ever.
The CDC found that about half of those who received the booster went on to test positive for COVID. However, the updated booster vaccine reduced the risk of death from COVID by more than twofold compared to vaccinated people without the bivalent booster, and by nearly 13-fold for those who have never been vaccinated for COVID.
Overall, the shot cuts the risk of symptomatic infection by about half, but people will see different results and benefits based on risk factors, said Ruth Link-Gelles, author of the study.
In 2020, the original Pfizer and Moderna COVID-19 vaccines reduced symptomatic infections by 95%, as seen in clinical trials.
But as COVID continued to mutate and new variants were formed, the shots began to lose their strength.
The vaccines fell to 36% effective at preventing illness by the time the first omicron variant became the main strain in late 2021.
Omicron and its subvariants led the vaccine producers to make updated shots to specifically target the new dominant variant. The bivalent booster shots were designed to boost immunity against omicron.
The omicron boosters contained the variant’s genetic code as well as a piece of the original strain.
As of mid-January, the XBB.1.5 subvariant made up 49% of CDC-sequenced COVID cases — and that’s expected to have risen since.
Despite a seemingly lower effectiveness rate, the CDC said that hospitalizations and deaths are still limited, and the vaccine rollout has been deemed a success.
