Covid omicron boosters provide some protection against the XBB variant

Pfizers and ModernOmicron boosters reduced the risk of mild disease from the XBB family of subvariants compared to people who didn’t get the shot, according to a Centers for Disease Control and Prevention study published Wednesday.

The CDC study provides the first estimate of the real-world effectiveness of the omicron shots against the XBB family of subvariants. Some scientists have warned that the XBB subvariants could trigger a new Covid surge because they are so good at evading the antibodies that block infection.

For people ages 18 to 49, the omicron booster reduced the risk of mild disease from XBB subvariants by about 48% two to three months after receiving the shot. According to the study, the injections provided 38% protection against mild disease for people ages 50 to 64 and 42% for people 65 and older.

Speaking to reporters Wednesday, CDC officials said the study results are reassuring because people who received the boosters had more protection than those who didn’t. Protection against serious illness should be higher, although data is not yet available, they said.

“It reduces your risk of symptomatic infection by about half on a population level,” said Dr. Ruth Link-Gelles, a CDC official and author of the study, on the 18 to 49 age group.

“In general, what we know from previous experience is that the vaccines protect better against more serious diseases,” Link-Gelles said. “So these are estimates for symptomatic infection and we would expect similar estimates for hospitalization and death to be higher.”

The XBB.1.5 subvariant is quickly becoming dominant in the US and currently makes up about 49% of new Covid cases nationwide. World Health Organization officials have described XBB.1.5 as the most transmissible version of the virus to date, although it has no mutations that suggest it makes people sicker than other subvariants.

XBB.1.5 is highly immune evasive and has mutations that allow it to better bind to human cells, scientists have discovered. But the CDC study indicates that the omicron boosters provide about as much protection against the XBB family as against the BA.5 and its descendants such as BQ.1 and BQ.1.1.

For example, adults aged 18 to 49 who received the Omicron booster had a 52% lower risk of mild disease from BA.5 and its offspring, compared to a 48% lower risk for the XBB family.

“We saw no reduced vaccine protection against symptomatic disease for XBB and XBB.1.5 compared to those other recent BA.5 variants,” said Dr. Brendan Jackson, chief of the CDC’s Covid-19 response.

The study compared people who received the new booster to those who received between two and four doses of the original vaccine. The boosters target omicron BA.5 and the original Covid strain that emerged in Wuhan, China, while the old shots only targeted the original virus strain.

People who received only the original injections generally received their last dose about 13 months ago. They had very little protection against mild disease because of the waning immunity seen with the old vaccines, Link-Gelles said. It’s too early to draw conclusions about how protection against the Omicron boosters holds up over time, she said.

“Even though you have reduced protection against symptomatic infection over time, you are likely still protected against more serious disease for a longer period of time,” Link-Gelles said.

The CDC study looked at the test results of about 29,000 people from December through January 13. Over that period, XBB.1.5 rose from 2.4% of cases to about 37%. Of the more than 13,000 individuals who tested positive, 78% developed a BA.5-related subvariant and 22% developed an XBB-related subvariant.

The study did not perform a detailed genomic analysis on every positive test sample to determine with 100% certainty which subvariant caused the infection. Instead, the scientists used a quark in PCR testing to determine which variant was likely causing the infection.

BA.5-related subvariants have a mutation that deletes a gene on the virus peak targeted by the tests, while XBB subvariants do not have this deletion. If the gene is detected it is probably XBB and if it is not detected it is probably BA.5 related.

Leave a Comment