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What’s the difference between Pirola, Eris and Pi? Covid variants explained

New mutated variants are ‘competing with each other’ as experts warn new waves expected in winter

Maryam Zakir-Hussain
Thursday 07 September 2023 08:24 BST
Inside new vaccine centre launched in UK to help scientists prepare for ‘disease X’

New Covid variants continue to spread across the globe as experts are warning cases will rise as the summer ends.

Three Omicron strains have emerged showing significant mutations from the original variant.

The arrival of Eris, Pi and most recently, Pirola, coincides with unsettled weather and “small but significant” rising hospital admissions in England.

It comes as the UK has seen 93,083 new cases of Covid as of 3 September, according to The Zoe Health Study.

The UK Health Security Agency (UKHSA) said the Covid-19 cases and ICU admissions continued to rise in its latest update, while hospital admission rates have increased in most age groups.

Here is everything you need to know about the new Covid variants:


Pirola, or BA.2.86, is the latest Omicron variant to appear this summer, with 34 more mutations than the BA.2, according to virologist Professor Lawrence Young.

According to the Centers for Disease and Control Prevention, as of 23 August, there were two cases of BA.2.86 detected in the US.

One of the cases is in a person detected through the CDC’s Traveler-based Genomic Surveillance and the “identification of these cases in multiple geographies is evidence of international transmission,” the CDC reported.

However, the CDC noted that the current hospitalisations in the country are not “likely” driven by BA.2.86, but added, “this assessment may change as additional data become available.”

Globally, the variant has been detected in Denmark, South Africa, Israel, the United Kingdom and the US.


A descendant of Omicron, Eris, or EG.5.1, was first classified as a variant by the World Health Organisation (WHO) on 9 August. It is the second most prevalent variant in the UK after Arcturus, XBB.1.16, and the most common variant in the US, according to the Centers for Disease Control and Prevention (CDC).

Eris was initially raised as a signal in monitoring on 3 July 2023 due to increased reports internationally, particularly in Asia, the UKHSA reported.

According to prof Young, a key difference for Eris from other Omicron variants is that it has an additional mutation (F456L) in the spike protein “which might account for its ability to evade the neutralising antibody response from previous Omicron infections”.


Pi, or BA.6, is another variant of Omicron. It has only been sequenced so far in Denmark and Israel since 24 July.

Head of primary care and public health at Imperial College London, Professor Azeem Majeed said the variant “is not currently very commonly identified in people infected with Covid-19”.

Professor Christina Pagel said Sky News that although it is “very, very early days” Pi has “a lot of new mutations that make it very different to previous Omicron strains”.

The arrival of Eris, Pi and most recently, Pirola, coincides with unsettled weather this summer in the UK (PA Archive)

What are the symptoms?

All three variants are strains of Omicron. According to the ZOE Health Study, the five most common symptoms of Omicron are:

  • Runny nose
  • Headache
  • Fatigue (mild or severe)
  • Sneezing
  • Sore throat

However, three more symptoms which have been commonly reported are diarrhea, eye irritation and rashes, according to the New Scientist.

How worried should we be?

Prof Young told The Independent said the new mutated variants are “competing with each other and are continuing to change as they spread”.

He added: “We are already seeing a rise in symptomatic covid infections and a small but significant increase in hospitalisations due to Covid.

“It is very likely that we will see waves of infection over the winter. The hope is that, with various mitigations including autumn vaccine boosters with XBB-lineage updated mRNA vaccines, these will be small waves.”

Prof Majeed said that despite “concerns” new variants will be able to “evade immunity and cause more serious disease than previous variants,” prior immunity from vaccination and infection “continues to provide good protection for most people”.

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