Meanwhile, the highly transmissible Omicron subtype XBB.1.5 — nicknamed “kraken” by some — is now the dominant SARS-CoV-2 strain in the United States, predicted by the CDC to account for more than 49 percent of cases in the country. Last week.
Earlier this month, the WHO said XBB.1.5 is the most prevalent variant to date, and toured dozens of countries. Although the wave of disaster has not yet risen in the US, deaths have increased this month, with an average of 564 people dying from Covid-19 each day through January 18, compared to an average of 384. Same time in December.
The A new vaccine efficacy study, Using data from the National Pharmacy Program for Covid testing, a bivalent booster provided 48 percent greater protection against symptomatic infection from subtypes XBB and XBB.1.5 compared with those who received a booster in the previous two to three months. who had previously received only two to four monovalent doses.
It conferred 52 percent greater protection against symptomatic infection from the BA.5 subvariant, although the CDC estimates that BA.5 accounted for only 2 percent of US cases last week.
CDC officials cautioned that the findings reflect population-wide protection rates, and individual risk of infection varies.
“Because every person is different, it’s hard to interpret that as an individual’s risk,” said Ruth Link-Kelles, author of the vaccine effectiveness study published in MMWR Wednesday. “Their immune system is different, their history of previous infection is different. They may have underlying conditions that put them at greater or lesser risk for Covid-19.”
He added that given the study’s limitations, it’s unclear how long the bivalent booster’s protection would last.
“It’s too early to know how the reduction will happen with the bivalent vaccine,” he said. “What we’ve seen in the past is that your protection against severe disease lasts longer. So, even if your protection against symptomatic infection wanes over time, you’re still protected against severe disease for a long time.