The Omicron variant of concern has given rise to many new sublineages, including the BA.1 and BA.2 that were predominant in South Africa from November 2021 through March 2022. BA.4 and BA.5 became predominant in April 2022 and remained the predominant circulating sublineages throughout 2022. As of 9 January 2023, more than 650 sublineages of Omicron have been identified, of which more than 200 have been detected in South Africa. In September 2022, a new sublineage XBB was identified in the United States of America (USA) and Singapore. XBB is a recombinant of two BA.2 sublineages which means it contains the genetic material of both parent sublineages.
The XBB sublineage has been shown to have increased immune evasion compared to previous sublineages. Since its identification, the XBB sublineage has given rise to several more sublineages, including XBB.1, XBB.2, and XBB.3, that have been circulating in South Africa since October 2022. The XBB.1.5 sublineage was first detected in October 2022 in the USA and has since been detected in several other countries, with the first detection in South Africa from a sample collected late in December 2022. With the growing distribution of XBB.1.5, it was not unexpected that it would be detected in South Africa. XBB.1.5 has been shown to have a growth advantage in the USA compared to previous variants, which means it may outcompete other variants to become the dominant circulating variant in some settings. This sublineage is now being monitored as a “subvariant of concern”. The growth advantage is thought to be due to a substitution (F486P) in the spike protein that increases the binding of the virus to the human ACE2 receptor and therefore increases the transmissibility of the virus.
Thus far, it is not known if the severity of infection will be different to other Omicron sublineages. The World Health Organization (WHO) Technical Advisory Group on Virus Evolution is currently conducting an ongoing risk assessment on XBB.1.5.
Due to the widespread circulation of other Omicron sublineages, and the overall high population immunity in South Africa, the introduction of XBB.1.5 in South Africa may not necessarily result in a large wave of infections. Ongoing surveillance to track variants will continue to track the growth of XBB.1.5 in South Africa and information is published weekly on the NICD website. All private and public laboratories are requested to send positive SARS-CoV-2 specimens for genomic sequencing. Currently, no changes to the public health response are required, and individuals are encouraged to receive SARS-CoV-2 vaccination and boosters, as recommended by the National Department of Health, because vaccination has been shown to reduce the risk of hospitalisation and death.
