Pfizer‘sand ModernOmicron’s omicron boosters reduced the risk of mild illness from the XBB subvariant family compared to people who did not receive the injection, according to a Centers for Disease Control and Prevention study released Wednesday.
The CDC study provides the first estimate of the true effectiveness of omicron injections against the XBB family of subvariants. Some scientists have warned that the XBB subvariants could cause another wave of Covid because they are so good at evading antibodies that block infections.
For people aged 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 injection. The injections provided 38% protection against mild disease for people aged 50 to 64 and 42% for people aged 65 and over, according to the study.
CDC officials, in a call with reporters Wednesday, said the study results are reassuring because people who received the boosters had more protection than those who did not. Protection against serious diseases should be higher although this data is not yet available, they said.
“This roughly halves the risk of symptomatic infection at the population level,” CDC official and study author Dr. Ruth Link-Gelles said of the 18-49 age group. .
“What we know from past experience is that vaccines generally protect better against more serious diseases,” Link-Gelles said. “So these are estimates of symptomatic infection and we would expect similar estimates of hospitalization and death to be higher.”
The XBB.1.5 subvariant is rapidly becoming dominant in the United States and currently accounts for approximately 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 suggesting it makes people sicker than other subtypes. variants.
XBB.1.5 is highly evasive of the immune system and has mutations that allow it to bind better to human cells, the scientists found. But the CDC study indicates that omicron boosters offer about as much protection against the XBB family as against BA.5 and its descendants such as BQ.1 and BQ.1.1.
For example, adults aged 18-49 who received the omicron booster had a 52% reduced risk of mild disease from BA.5 and its progeny, compared to a 48% reduced risk for the XBB family.
“We did not see a reduction in vaccine protection against symptomatic disease for XBB and XBB.1.5 compared to these other recent BA.5 variants,” said Dr Brendan Jackson, Covid-19 Response Manager. from the CDC.
The study compared people who received the new booster with those who received between two and four doses of the original vaccine. The recalls target omicron BA.5 and the original Covid strain that emerged in Wuhan, China, while the old shots only target the original virus strain.
People who only received the original injections usually received their last dose about 13 months ago. They had very little protection against mild illnesses due to the decreased immunity seen with older vaccines, Link-Gelles said. It’s too early to draw conclusions about how the protection of omicron boosters holds up over time, she said.
“Even though you may have reduced protection over time against symptomatic infection, you’re likely still protected against more severe disease for a longer period of time,” Link-Gelles said.
The CDC study looked at the Covid test results of about 29,000 people from December through January 13. During this period, XBB.1.5 increased from 2.4% of cases to around 37%. Of the more than 13,000 people who tested positive, 78% caught a BA.5-related subvariant and 22% caught an XBB-related subvariant.
The study did not perform detailed genomic analysis on each positive test sample to determine with 100% certainty which subvariant caused the infection. Instead, the scientists used a quark in the PCR tests to determine which variant was likely causing the infection.
BA.5-like subvariants have a mutation that deletes a gene on the viral spike targeted by the assays, while XBB subvariants lack this deletion. If the gene is detected it is probably XBB and if not detected it is probably related to BA.5.