Meanwhile, the highly transmissible subvariant of Omicron XBB.1.5 – dubbed “the Kraken” by some – is now the dominant strain of SARS-CoV-2 in the United States, projected by the CDC to represent slightly more 49% of cases in the country as of last week.
Earlier this month, the WHO has declared XBB.1.5 to be the most transmissible variant to date, and circulates in dozens of countries. Although a catastrophic wave has not yet emerged in the United States, there has nevertheless been a spike in deaths this month, with an average of 564 people dying from Covid-19 every day as of January 18, compared to a average of 384 around the same time in December.
The new vaccine efficacy study, which used data from the National Pharmacy Program for Covid testing, found that the bivalent booster provided 48% greater protection against symptomatic infection of the XBB and XBB subvariants. 1.5 in people who had received the booster in the previous two to three months, compared to people who had previously received only two to four monovalent doses.
It also provided 52% greater protection against symptomatic infection of the BA.5 subvariant, although according to CDC estimates, BA.5 accounted for only about 2% of US cases last week.
CDC officials cautioned that the results reflected a population-level protection rate and that individual risk of infection varied.
“It’s hard to interpret it as an individual risk because every individual is different,” said Ruth Link-Gelles, the author of the vaccine efficacy study published in MMWR on Wednesday. “Their immune system is different, their history of previous infection is different. They may have underlying conditions that put them at more or less risk for COVID-19 disease.”
She also said it’s unclear, given the limitations of the study, how long the bivalent booster protection will last.
“It’s too early to know how the decline will happen with the bivalent vaccine,” she said. “What we’ve seen in the past is that your protection lasts longer for the most serious illnesses. So, even if you have reduced protection over time against symptomatic infection, you are likely still protected against more severe disease for a longer period of time.
#booster #works #dominant #strain #Covid
