New Covid variant Arcturus: symptoms, how infectious is it, vaccine efficacy and UK cases so far

A new Covid variant behind a surge of infections in India has now been detected in the UK, sparking concerns of a fresh uptick in cases.

Named Arcturus - also known as XBB.1.16 - the strain is a subvariant of Omicron and was first identified in January this year.

The World Health Organisation (WHO) has been monitoring it since 22 March and warned it is “one to watch” as it has one additional mutation in the spike protein which, in lab studies, shows “increased infectivity”.

It is currently classified by the WHO as a new variant “under monitoring”, which is less serious than those labelled “of interest” or “concern”.

Here’s what you need to know about how infectious it is, what symptoms it causes, its impact on vaccines and case numbers in the UK so far.

How infectious is the new Covid variant?

Research indicates Arcturus could be one 1.2 times more infectious than the last major sub-variant, which was Omicron.

It has a similar profile to its predecessor XBB.1.5 - Omicron - but it has an additional mutation which, according to lab studies, makes it more infectious and potentially more pathogenic, Maria Van Kerkhove, WHO’s technical lead for Covid-19, said at a press conference last month.

The WHO says this does not indicate that it is causing more severe disease among those who are infected, but noted that it is “one to watch”. But the spike protein mutation makes the new variant more capable of escaping antibodies from previous immunity gained either from vaccination or infection.

Ms van Kerkhove explained: “It’s actually very similar in profile to XBB.1.5. It has one additional mutation in the spike protein which in lab studies shows increase infectivity, as well as potential increased pathogenicity. So, it’s one that we are monitoring (...) because it has potential changes that we need to keep a good eye out on.”

How many cases are there in the UK?

The Arcturus variant has so far been detected in 29 countries, including the UK, the US, Australia and Singapore.

Most of the samples of Arcturus are from India, where weekly Covid cases more than doubled in a week - although infections still remain far below peak levels, according to WHO data.

The UK Health and Security Agency (UKHSA) said the strain was already in the UK in its final variant report issued last month. A total of 66 sequences of the new variant have been recorded in the UK up to 11 April, according to the UKHSA.

It said: “XBB.1.16 is a lineage with three additional spike mutations (E180V, K478R, and S486P) found both in the UK and internationally. However, the number of total number of samples is still less than 100.”

Omicron still remains the dominant variant of concern across the world.

What are the symptoms of Arcturus?

The main symptoms of Arcturus reported so far include a high fever, a cough and “itchy” conjunctivitis, with the latter being particularly common among children.

Conjunctivitis - also known as red or pink eye - usually affects both eyes and can make them become red and itchy, watery, produce pus that sticks to lashes, and they may burn or feel gritty.

Dr William Schaffner, professor of preventive medicine, health policy, and professor, Division of Infectious Diseases at Vanderbilt University, said the additional mutation in the spike protein makes Arcturus “even more contagious than Omicron”, but its symptoms do not tend to be particularly severe.

He told Healthline: “It has a tendency to produce a high fever. Omicron can produce a fever, but many people get infected who don’t have a fever at all. The cause for the fever in the Arcturus variant is because of an inflammatory response in the body, which is distinctive in this variant.

“The other thing that is even more distinctive is that, particularly in children, it has the tendency to produce conjunctivitis, which is the inflammation of the outside of the eye.”

Do vaccines protect against the Arcturus variant?

Early results suggest that Arcturus does not have any increased ability to evade protection from vaccines compared to previous Omicron variants.

It means that those who have received the vaccines and booster jabs should have a level of defence against severe disease from the new variant.

As for whether the Arcturus is more severe than previous strains, reports so far do not indicate a rise in hospitalisations, ICU admissions or deaths due to the variant.