Despite its rapid spread in the country, initial analyses show no difference in hospitalizations between the BA.2 subvariant and the original form of Omicron, also known as BA.1.
Studies, however, are still ongoing to understand the infectiousness of BA.2, alongside how effective vaccines are against it.
While BA.2 is not currently a “variant of concern,” public health officials in the U.K. The UK Health Security Agency (UKHSA) has published analyses of Omicron sub-lineage BA.2. Data by variant related to intensive care unit admissions is presented and an analysis into the effect of the recent surge of Omicron cases in care homes is also available in the latest.
Omicron sub-lineage BA.2 (VUI-22JAN-01)
As of 24 January 2022, 1,072 genomically confirmed cases of BA.2 have been identified in England and all assessments remain preliminary whilst case numbers are relatively low.
BA.2 has an increased growth rate compared to BA.1 in all regions of England where there are enough cases to assess it. While growth rates can be overestimated in early analyses of a new variant, the apparent growth advantage is currently substantial.
Analysis from routine contact tracing data indicates that transmission is likely to be higher among contacts of BA.2 cases in households (13.4%) than those for contacts of other Omicron cases (10.3%) in the period 27 December 2021 to 11 January 2022. These early findings should be interpreted with caution as transmission data and dynamics can fluctuate, meaning that early findings can change quickly when new variants are identified.
A preliminary assessment did not find evidence of a difference in vaccine effectiveness against symptomatic disease for BA.2 compared to BA.1. After 2 doses, vaccine effectiveness was 9% and 13% respectively for BA.1 and BA.2, after 25+ weeks. This increased to 63% for BA.1 and 70% for BA.2 at 2 weeks following a third vaccine.
There is currently no data on the severity of BA.2. UKHSA will continue to carry out laboratory and epidemiological investigations to better understand the characteristics of this variant.
Dr Susan Hopkins, Chief Medical Advisor for UKHSA, said:
Ongoing variant analysis is an important part of our pandemic response. Thanks to the expertise of scientists at UKHSA and partner organisations, we’re able to respond quickly to new variations of the virus.
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.
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. Consider wearing a face covering when in crowded places. Take a vaccine to protect yourself against COVID-19. If you have any symptoms, take a test.
Omicron data
UKHSA has also published analyses related to the original Omicron strain BA.1. Where variant information was available, the majority of intensive care unit (ICU) admissions from 24 November 2021 to 19 January 2022 had Delta infections. Overall numbers of ICU admissions have decreased over time, but where data was available admissions with Omicron have increased from 9% to more than 50% in the most recent week.
Although there was a rapid increase in SARS-CoV-2 infections in care homes during December 2021 in line with case rises in the community, there has not been an associated increase in hospital admissions.
Our findings suggest the current wave of Omicron infections is unlikely to lead to a major surge in severe disease in care home populations with high levels of vaccine coverage and/or natural immunity. There were very limited numbers of BA.2 in this study and no inferences can be made regarding BA.2.
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