Omicron sub-lineage BA.2 has substantial 'growth advantage' over original, UK finds

London: The BA.2 sub-lineage of the Omicron variant of COVID-19, which is classed as a variant under investigation in the UK, spreads much faster than the original BA.1 strain but it also seems to show higher vaccine protection, health authorities said.

The UK Health Security Agency (UKHSA) said that BA.2 has an increased growth rate compared to BA.1 in all regions of England where there are enough cases to assess it. As of January 24, 1,072 genomically confirmed cases of BA.2 have been identified in England and all assessments remain preliminary whilst case numbers are relatively low.

While growth rates can be overestimated in early analyses of a new variant, the apparent growth advantage is currently substantial, the UKHSA said.

The experts said their analysis from routine contact tracing data indicates that transmission is likely to be higher among contacts of BA.2 cases in households at around 13.4 per cent than those for contacts of other Omicron cases at 10.3 per cent in the period between December 27, 2021, to January 11, 2022.

A linked preliminary assessment did not find evidence of a difference in vaccine effectiveness against symptomatic disease for BA.2 compared to BA.1. After two doses, vaccine effectiveness was 9 per cent and 13 per cent respectively for BA.1 and BA.2, after 25+ weeks. This increased to 63 per cent for BA.1 and 70 per cent for BA.2 at 2 weeks following a third vaccine.

We now know that BA.2 has an increased growth rate which can be seen in all regions in England. We have also learnt that BA.2 has a slightly higher secondary attack rate than BA.1 in households, said Dr Susan Hopkins, Chief Medical Advisor for UKHSA. Although hospitalisations and deaths remain low, cases are still high in some areas and some age groups so it's important that we continue to act cautiously as restrictions are lifted, she said. In its latest update on Omicron data, the UKHSA notes that overall numbers of intensive care unit (ICU) admissions have decreased over time, but where data was available admissions with Omicron have increased from 9 per cent to more than 50 per cent in the most recent week.

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