India’s first case of the XBB.1.5 subvariant of the Omicron variant of the coronavirus was confirmed in Gujarat by the national genome sequencing consortium on December 31, 2021.

  • 1.5 has been driving a surge in COVID-19 cases in the United States and is highly transmissible, evading pre-existing immunity, although it does not seem to cause severe disease.
  • The global prevalence of XBB.1.5 is not yet clear, although its parent strain has been detected in at least 35 countries. By December 30, 2021, XBB.1.5 accounted for 40.5% of all new cases in the US, up from 21.7% a week earlier.

Origin of the XBB.1.5 Variant:

  • 1.5 is a recombinant variant, which means its genome is the result of the genomes of two different strains spliced together. This can occur when two strains infect a person at the same time and a recombinant variant is produced as they replicate together.
  • Recombinant strains can also arise when existing recombinant strains mutate. The defining mutation of XBB.1.5 is F486P, which is located in the virus’s receptor-binding domain and is an important site targeted by antibodies against the Omicron variant.
  • F486P is an unlikely mutation, requiring two nucleotide substitutions, and could reduce the effectiveness of Eli Lilly’s monoclonal antibody bamlanivimab.

Transmissibility of XBB.1.5:

  • Studies have found that XBB.1.5 is more immune-evasive than previous strains, including XBB and XBB.1, and that it is better at binding to ACE2 receptors in the body, making it more transmissible.
  • It is also less susceptible to neutralisation by vaccines, including those based on mRNA technology. While XBB.1.5 is highly transmissible, there is currently no evidence to suggest that it causes more severe disease.

Impact on Vaccines:

  • There are concerns that the XBB.1.5 variant could impact the effectiveness of vaccines, as it appears to be less susceptible to neutralisation by existing vaccines.
  • This could mean that people who have been vaccinated may still be at risk of contracting the variant and experiencing mild or asymptomatic infection.
  • However, it is worth noting that the vaccines currently being administered have been shown to be effective at preventing severe illness and death from COVID-19, and it is still recommended for individuals to get vaccinated.
  • It is also important for researchers and vaccine manufacturers to continue monitoring the emergence and spread of new variants and to work on developing booster shots or alternative vaccines as needed.
  • The global rollout of vaccines has also been slowed by the emergence of new variants, which highlights the importance of continuing efforts to control the spread of the virus and reduce the opportunity for further mutation.

The XBB.1.5 variant is a cause for concern due to its high transmissibility and ability to evade pre-existing immunity. While it does not seem to cause severe disease, it could impact the effectiveness of vaccines and pose a risk to individuals who have been vaccinated. It is important for countries to continue monitoring the spread of this and other variants and to take steps to control the spread of the virus, including implementing public health measures and promoting vaccination.

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