On 15 March 2023, WHO announced that, going forward, the Greek letters will only be assigned to VOCs, while VOIs will be referred to using established scientific nomenclature systems such as those used by Nextstrain and Pango (e.g. XBB.1.5/23A for the latest VOI). WHO and TAGVE will undertake regular risk assessments for both VOIs and VOCs.
A SARS-CoV-2 variant that meets the definition of a VOI (see above) and, through a risk assessment, conducted by WHO TAG-VE, and determined to be associated with a moderate or high level of confidence, meets at least one of the following criteria when compared with other variants:
XBB.1.16 is a descendent lineage of XBB, a recombinant of two BA.2 descendent lineages. XBB.1.16 was first reported on 09 January 2023, and designated a variant under monitoring (VUM) on 22 March 2023. On 17 April 2023, XBB.1.16 was designated a variant of interest (VOI). XBB.1.16 has a similar genetic profile as the VOI XBB.1.5, with the additional E180V and K478R amino acid mutations in the spike protein compared to their parent XBB.1.
As of 17 April 2023, 3648 sequences of the Omicron XBB.1.16 variant have been reported from 33 countries (GISAID, XBB.1.16 searched using variant defining nucleotide mutations T12730A, T28297C, A28447G). The majority of the XBB.1.16 sequences are from India (63.4%, 2314 sequences). The other countries with at least 50 sequences include the United States of America (10.9%, 396 sequences), Singapore (6.9%, 250 sequences), Australia (3.9%, 143 sequences), Canada (2.6%, 94 sequences), Brunei (2.4%, 89 sequences), Japan (2.0%, 73 sequences) and the United Kingdom (2.1%, 75 sequences).
Globally, there has been a weekly rise in the prevalence of XBB.1.16. During epidemiological week 13 (27 March to 2 April 2023), the global prevalence of XBB.1.16 was 4.15%, an increase from 4 weeks prior (epidemiological week 9, 27 February to 5 March 2023), when the global prevalence was 0.52%.
| Indicator | Level of Risk | Level of Confidence | |
|---|---|---|---|
| Growth Advantage |
Comparing the month of February and the month of March 2023 in India, the proportion of XBB1.16 relative to other circulating variants rose from 15.3% (137/895) to 58.6% (2,130/3,636). Similarly for countries with more than 100 From WHO’s internal variant growth rate analysis, similarly used by the UKHSA, XBB.1 family of variants, which includes XBB.1.16, have the fastest growth over Nextstrain has designated XBB.1.16 a new clade 23B based on a criteria of “>0.05 per day growth in frequency and >5% regional frequency”, whereby from their |
Moderate | High |
| Antibody Escape |
Similar to XBB.1 and XBB.1.5, XBB.1.16 neutralization assays have demonstrated resistance to BA.2 and BA.5 breakthrough infection sera. The sensitivity of XBB.1.16 to convalescent sera of XBB.1-infected hamsters was comparable to those of XBB.1 and XBB.1.5, which points at a similar ability of these variants to evade immunity. |
Moderate | Low |
| Severity and Clinical Considerations |
An analysis of infections from India did not report any differences in hospitalization and oxygen requirement for XBB.1.16 as compared to other circulating lineages (Dr. Rajesh Karyakarte’s, BJ Government Medical College, Pune). In terms of clinical considerations, there has been a slight rise in bed occupancy in some states in India (2-4%). However, these levels are much lower compared to the level recorded during the Delta wave or Omicron BA.1/BA.2 wave. Disease severity is not higher compared to previously circulating variants. In India, >70% of the population have received a booster vaccine dose. The antiviral sotrovimab exhibits antiviral activity against XBB.1.16, similar to other XBB subvariants. |
Low | Moderate |
|
Overall Risk Assessment
Low |
Based on its genetic features, immune escape characteristics and growth rate estimates, XBB.1.16 may spread globally and drive an increase in case incidence. From reports from India and other countries, no early signals of increases in severity have been observed. As XBB.1.16 has spread to 33 countries, disease severity is being monitored carefully. Taken together, available evidence does not suggest that XBB.1.16 has additional public health risks relative to the other currently circulating Omicron descendent lineages. |
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