‘Small number’ of Omicron sub-lineage detected in State

There has been a “small number” of cases of a sub-lineage of the Omicron variant detected in the State, a public health official has said.

However, Cillian De Gascun, director of the National Virus Reference Laboratory, said there are indications that the presence of BA.2 could be rising.

According to the World Health Organisation (WHO), the Omicron variant has three main sub-lineages: BA.1, BA.2 and BA.3.

BA.1 was largely responsible for the surge in Omicron cases over the winter period, according to the WHO, which resulted in record-breaking case numbers detected in many countries.

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However, the prevalance of the BA.2 sub-lineage has increased internationally in recent weeks. It has already become dominant in Denmark and is likely to become dominant in the UK in the coming weeks.

The UK Health Security Agency has declared the sub-lineage a “variant of investigation”, with early analysis suggesting it has a growth advantage when compared to BA.1.

Severity

There is currently no data on the severity of BA.2 compared to BA.1, and a preliminary assessment by UK officials did not find a difference in vaccine effectiveness against symptomatic disease between the two.

In response to questions from The Irish Times, Mr De Gascun said the UK risk assessment “doesn’t give too much cause for alarm at this stage”.

The difference in mutations between the two subtypes allows officials to monitor the emergence of BA.1 through genome sequencing, he added.

BA.1 can be detected by PCR tests with S gene target failure [SGTF], while BA.2 differs because the S gene is detectable.

“So, while we’ve seen only small numbers of BA.2 cases in our sequencing to date, the SGTF proportion has declined from 97 per cent to 93 per cent over the last few days, so that could signal the start of something, which we will of course continue to monitor,” Mr de Gascun said.

Genome sequencing

According to figures from the Health Protection Surveillance Centre (HPSC), some 2,936 cases of Covid-19 in Ireland have been identified as the Omicron variant through genome sequencing between November 25th and January 17th.

Of those, 2,926 were BA.1, nine were BA.2 and one was BA.3.

The WHO has said that investigation into the characteristics of BA.2, including virulence, should be “prioritised independently (and comparatively) to BA.1”.

Meanwhile, the National Public Health Emergency Team (Nphet) reported an additional 5,109 PCR-confirmed cases of Covid-19 on Friday.

In addition, 4,482 people registered a positive antigen test through the HSE portal on Thursday.

As of 8am on Friday, 707 Covid-19 patients were hospitalised, of whom 69 were in ICU.

The Department of Health said it will no longer report daily case numbers at the weekends. Covid cases reported on Mondays will take account of weekend figures, it added.