#16,564
Although BA.2 isn't spreading as fast in the UK as it has in Denmark (Denmark SSI: Omicron Variant BA.2 Rising - Expected To Soon Comprise 100% Of Cases) it is slowly gaining ground, and will likely become the UK's dominant strain in the weeks to come.
Considered a `sister' of BA.1, not a descendent, BA.2 looks to be the heir apparent to the current Omicron variant. How it differs from BA.1 is still under investigation.
Today the UKHSA has published a new Technical report, and Risk Assessment on BA.2 (excerpts below). Follow the link to access the full 33-page document.
SARS-CoV-2 variants of concern andvariants under investigation in England
Technical briefing 36
11 February 2022
VUI-22JAN-01 (BA.2)
As of 7 February 2022, 7,194 genomically confirmed cases of BA.2 have been identified in England. Sequencing data is complete up to 31 January, at which point 95.4% of sequences were BA.1, 4.1% were BA.2 and 0.5% were other lineages. BA.2 does not contain the spike gene deletion at position 69-70 and is S-gene target positive (SGTP) on polymerase chain reaction (PCR) diagnostic assays with targets in this area. SGTP is now a reasonable proxy for BA.2, accounting for 97% of sequenced SGTP cases with an increasing trend.
The proportion of SGTP cases is now increasing. As of 6 February 2022, the overall proportion of SGTP cases in England is 18.7% compared to 5.1% on 24 January. There is geographical variation with the highest proportion in London (31%) and the lowest in the North-East region (3.9%).
Growth rate
BA.2 has an increased growth rate compared to BA.1 in all regions of England. Whilst growth rates can be overestimates early in the emergence of a variant, the apparent growth advantage is currently substantial.
Reinfections
Although a limited proportion of samples are sequenced, there is no detected sequence confirmed BA.2 reinfection following a BA.1 infection at any interval to date in England.
Serial interval
Preliminary analysis from contact tracing data suggests that the average time from symptom onset of a primary case to symptom onset in their identified contacts (the mean serial interval) is around half a day shorter for BA.2 than BA.1, with a mean serial interval of 3.27 days compared to 3.72 days for BA.1. Both are shorter than the mean serial interval for Delta of 4.09 days. The serial interval suggests the time between primary and secondary infections is shorter, which could contribute to the increased growth rate of BA.2.
Neutralisation data and vaccine effectiveness
Oxford University reports neutralisation studies using monoclonal antibodies and some preliminary studies using sera suggest a small antigenic difference between BA.1 and BA.2, which is expected from the mutation profile. However, sera from individuals with recent booster vaccinations neutralise both variants similarly. Neutralisation studies use recent vaccinee sera and it is unclear whether the difference between variants will increase as the responses wane. There is no detected change in vaccine effectiveness against symptomatic infection in England though international data are noted in the COVID-19 vaccine surveillance report.
Updated risk assessment An updated risk assessment for VUI-22JAN-01 (BA.2) has been published :
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1054345/9-February-2022-risk-assessment-for-VUI-22JAN-01__BA.2_.pdf
While there is no evidence to suggest that BA.2 infection is any more severe than BA.1, this latest risk assessment continues to cite:
Insufficient data No systematic analyses comparing BA.1 and BA.2 are as yet available.
We should have better data on BA.2's severity in the next few weeks.
