Omicron outcompetes omicron, official data

Risk assessment for SARS-CoV-2 variant: VUI-22JAN-01 (BA.2)

Assessment and rationale

Omicron BA.1 is currently the dominant variant in the UK

This risk assessment uses the characteristics of BA.1 as the baseline

Overall growth advantage, Red, moderate

There is evidence of a growth advantage for BA.2 compared to BA.1 in more than one country

UK data, evidence of increased growth of BA.2 compared to BA.1

All regions of England where there are sufficient cases to assess

Observed growth advantage, supported by increased household secondary attack rates in UK data

Growth advantage 1: Transmissibility, Red, low

It is plausible that transmissibility is contributing to the growth advantage,

given the high secondary attack rates and lack of apparent immune evasion

It is unclear at present how this would arise from the BA.2 mutation profile.

Growth advantage 2: Immune evasion, Amber, low

Based on early data BA.2 does not appear to be more immune evasive than BA.1

Bases on vaccinee sera

A preliminary neutralisation study does not suggest a difference in neutralisation between BA.1 and BA.2

There is no live virus data available in the UK

Vaccine effectiveness against symptomatic disease, no suggested difference between BA.1 and BA.2

Infection severity

Insufficient data

No systematic analyses comparing BA.1 and BA.2 are as yet available

Cumulative cases in England of variants indexed by days since the fifth reported case

Data cut-off of 24 January 2022, BA.2

Sequencing data is complete up to 16 January

96.1% of sequences were BA.1

3.4% were BA.2

0.5% were other lineages

BA.2 does not contain the deletion at S:69-70,

and is S-gene target positive (SGTP) on PCR

The proportion of SGTP cases is now increasing

As of the 24 January 2022

Proportion of SGTP cases in England 4.4%

(2.2% on the 17 January)

London, 9.5%

North-East region, 0.9%

Growth rate

The apparent growth advantage is currently substantial

Secondary attack rates, household contacts

BA.2, 13.4%

Other Omicron cases, 10.3%

Data not adjusted for vaccination status, reflect overall growth advantage rather than transmissibility.

Vaccine effectiveness, 25 weeks after two doses

BA.1, 9%

BA.2, 13%

Vaccine effectiveness, 2 weeks after third after dose

BA.1, 63%

BA.s, 70%

BA.1 and BA.2 did not differ substantially in neutralisation by sera from vaccinated individuals

Omicron B.1.1.529/ BA.1, in care homes

There was a rapid increase in SARS-CoV-2 infections in care homes during December 2021,

there has not been an associated increase in hospital admissions

(no inferences can be made regarding BA.2)

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

Jonathan Ball, Professor of Molecular Virology at the University of Nottingham

The key issues are whether this variant is associated with more severe disease and if it can escape immunity delivered by vaccines.

Early indicators suggest that the vaccines will provide similar levels of protection as we have seen for omicron, so this is good news.

Whether or not it causes more severe disease will become apparent as more data is collected.

but so far there is nothing in these early analyses to worry us unduly

Professor John Edmunds, epidemiologist, London School of Hygiene & Tropical Medicine

Possible that BA.2 could take over from the original omicron strain in the next few weeks,

as it has done in Denmark.

The good news is that, at present, there is no evidence to suggest that it is more severe than omicron

and as the UKHSA analysis shows, the vaccines appear to be as effective against it as they are against BA.1