X FACTORS:

XBB.1.5 and XBB.1 are the omicron subvariants with the greatest immune-evasive properties. Therefore, one of the most contentious issues surrounding XBB.1.5 relates to the degree of protection afforded by currently available mRNA vaccines, including the latest bivalent booster formulations.

Researchers from the University of Texas determined that first-generation and bivalent mRNA booster vaccines containing BA.5 result in lackluster neutralizing antibody responses against XBB.1.5. A report (yet to be peer reviewed) from investigators at the Cleveland Clinic found that bivalent vaccines demonstrate only modest (30 per cent) effectiveness in otherwise healthy non-elderly people when the variants in the vaccine match those circulating in the community.

Furthermore, some experts believe the administration of bivalent boosters for the prevention of COVID-19 illness in otherwise healthy young individuals is not medically justified nor cost-effective.

In contrast, public health experts from Atlanta, Ga. and Stanford, Calif. reported that although the neutralizing antibody activity of bivalent booster vaccines against XBB.1.5 is 12 to 26 times less than antibody activity against the wild-type (original) SARS-CoV-2 virus, bivalent vaccines still perform better than monovalent vaccines against XBB.1.5.

However, investigators from Columbia University in New York found that neutralizing antibody levels following bivalent boosting were up to 155-fold lower against XBB.1.5 compared to levels against the wild-type virus following monovalent boosting.

This suggests that neither monovalent nor bivalent booster vaccines can be relied upon to provide adequate protection against XBB.1.5.

How can you protect yourself against XBB.1.5?

The rapid evolution of SARS-CoV-2 continues to pose a challenge for the management of COVID-19 illness using available preventive and therapeutic agents. Of note, all currently available monoclonal antibodies targeting the spike protein of SARS-CoV-2 are deemed to be ineffective against XBB.1.5.

Antiviral medicines such as remdesivir and Paxlovid may be considered for the treatment of eligible infected patients at high risk of progressing to severe disease.

Standard infection control precautions including indoor masking, social distancing and frequent handwashing are effective measures that can be employed for personal and population protection against XBB.1.5 and other subvariants of concern.

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