Covid variants: How many strains are in circulation and causing concern around the world?

With the world already battling to bring high rates of infection from the Omicron and Delta variants of Covid-19 under control this winter, news of the emergence of another new strain of the coronavirus has been met with dismay.

An Omicron sub-lineage dubbed BA.2 has been formally designated a “variant under investigation” by the UK Health Security Agency (UKHSA), with 426 cases confirmed in the UK so far, the earliest of which was detected on 6 December 2021.

“It is the nature of viruses to evolve and mutate, so it's to be expected that we will continue to see new variants emerge,” said Dr Meera Chand, incident director at the agency.

“Our continued genomic surveillance allows us to detect them and assess whether they are significant.

“So far, there is insufficient evidence to determine whether BA.2 causes more severe illness than Omicron BA.1, but data is limited and UKHSA continues to investigate.”

It is not clear where the sub-variant first emerged but the new strain has already been reported in 40 countries, including Denmark, India, Sweden and Singapore, according to the UKHSA.

For now, Omicron remains the main variant of concern, although cases in the UK appear to be falling after spiking over the New Year, prompting World Health Organisation (WHO) special envoy Dr David Nabarro to tell Sky News recently that there is “light at the end of the tunnel”.

“I think that it’s going to be bumpy before we get to the end,” he said, qualifying his optimism somewhat, and adding: “Even though it’s possible to start imagining that the end of the pandemic is not far away, just everybody be ready for the possibility that there will be more variations and mutations coming along, or that there will be further challenges, other surges of even Omicron coming.”

Leonardo Martinez, an infectious disease epidemiologist at Boston University, likewise told the AP: “The faster Omicron spreads, the more opportunities there are for mutation, potentially leading to more variants.”

If you need a reminder of the five coronavirus strains that are currently listed as global “variants of concern” by the WHO, they are as follows:

Alpha

Also known as B.1.1.7, first detected in Kent in the UK in September 2020 and since spread to more than 50 countries.

Beta

Also known as B.1.351, first detected in South Africa in May 2020 and spread to more than 20 countries, including the UK.

Delta

Also known as B.1.617.2, first detected in India in October 2020 and still the dominant strain in the UK, Europe and the US.

Gamma

Also known as P.1, first detected in Brazil in November 2020 and spread to more than 10 countries, including the UK.

Omicron

Also known as B.1.1.529, first detected in South Africa and Botswana in November 2021 and already detected in more than 110 countries, driving up infection rates due its increased transmissibility although its symptoms appear to be milder than those associated with the original virus.

In addition, the WHO lists two “variants of interest”, which are being monitored and tracked but are not presently thought to represent a significant public health threat:

Lambda

Also known as C.37, first detected in Peru in December 2020.

Mu

Also known as B.1.621, first detected in Colombia in January 2021.

Three further strains of the virus that were first recorded in January, May and September last year are listed as “variants under monitoring” and a further 17 strains have been relegated from that list because they are deemed no longer of concern after failing to circulate to any worrying extent.

The European Centre for Disease Prevention and Control currently lists the same variants of concern as the WHO, with the exception of the Alpha variant, which it has de-escalated due to “drastically reduced circulation”, due to the Delta variant usurping its position as the continent’s dominant Covid strain.

In the US, the Centres for Disease Control (CDC) currently only list Delta and Omicron as “variants of concern”.