World Health Organization advisers are recommending that vaccine makers formulate their Covid-19 shots to target XBB.1, the globally dominant, immune-evasive family of omicron strains.
(Bloomberg) — World Health Organization advisers are recommending that vaccine makers formulate their Covid-19 shots to target XBB.1, the globally dominant, immune-evasive family of omicron strains.
Manufacturers should also move away from using the original Wuhan strain in future shots, the WHO’s Technical Advisory Group on Covid-19 Vaccine Composition said. While currently available vaccines continue to provide good protection against severe disease, new data suggest vaccines targeting XBB.1 strains would generate better antibody responses than those targeting the older versions of the virus, Kanta Subbarao, the committee’s chair, said Thursday in Montreux, Switzerland.
“Protection against symptomatic illness really has dropped off with omicron,” Subbarao told the 16th International Nidovirus Symposium. “We believe that updates to the vaccine antigen composition may enhance vaccine-induced immune responses to circulating strains.”
The WHO is looking to provide Pfizer Inc., BioNTech SE, Moderna Inc. and other vaccine makers with guidance for how to best protect the world against the pandemic virus. The 16-member committee met last week in Geneva to make recommendations to WHO about ways to broaden immunity against Covid-19 including protection against future virus variants. The panel supports the use of monovalent vaccines that are based on single strains such as XBB.1.5 or XBB.1.16. These would broaden immune protection against the widely circulating omicron subvariants and new ones they spawn, Subbarao said.
The emergence of the highly mutated omicron variant in late 2021 led to an unprecedented spike in Covid cases worldwide. It’s so genetically different to previously circulating SARS-CoV-2 strains that some scientists have argued it represents a new serotype — as distinct from the Wuhan strain as that is from the original SARS virus that emerged two decades ago.
The XBB.1 lineage includes SARS-CoV-2 strains with the greatest magnitude of immune escape from neutralizing antibodies to date, Subbarao said.
Since omicron began spreading, alpha, delta and all other variants of concern have ceased to circulate in humans, she said. Repeated exposure to vaccines based on the original Wuhan strain may lead the immune system to respond less effectively to slightly altered versions.
The phenomenon called “immune imprinting” has also been seen with influenza, and increases the importance of using properly targeted vaccines that train the immune system to fight a broader array of viral versions.
The advisory group also encouraged vaccine makers to develop immunizations that generate a protective immune response in the mucosal lining of the nose and throat that promise to provide better protection against infection, and reduce SARS-CoV-2 transmission, Subbarao said.
Her committee is slated to meet at least every six months to review the data on circulating strains and vaccine effectiveness and make recommendations to WHO.
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