Covid Update – new variant ‘Arcturus’ first identified in India has spread to UK

 A new Covid sub-variant responsible for a surge of infections in India is giving rise to concerns that it could also lead to a significant rise in hospitalisations and deaths in the UK this autumn.

Research indicates that the new variant, named Arcturus, could be significantly more infectious than previous sub-variants in the Omicron series, which are still predominant throughout Europe and the USA.

Also known as Omicron sub-variant XBB.1.16, Arcturus was first identified in January and has been monitored by the World Health Organisation (WHO) since 22 March, which upgraded it to a “variant of interest” in mid-April.

WHO reports suggest that Arcturus doesn’t so far appear to be producing symptoms any more severe than the prevalent Omicron variants.  It has only one additional mutation in the spike protein, but lab investigations so far have confirmed it does exhibit increased infectivity over the other Omicron B variants, as well as the potential for increased pathogenicity. It also shows evidence of 'antibody escape' with a similar profile to XBB.1.5, a variant now circulating worldwide. One additional clinical symptom not so far seen with other  variants is conjunctivitis. 

Arcturus has been detected in 34 countries so far, including Britain and US.

It has already generated a significant new wave of infections in India, where the country’s health ministry reported 63,380 active Covid cases on 25 April. This is the result of a steady rise over a 6-week period, and has prompted compulsory face masks to be introduced in some states. Hospitals are on the alert for a new surge of Covid admissions, and production of the AstraZeneca vaccine is to be ramped-up under license in India.

India was devastated by the wave of Delta infections in 2021 and suffered a total of 4.7m excess deaths, according to WHO estimates.

Five deaths and around 135 cases attributable to Arcturus have been detected in the UK so far, according to the UK Health Security Agency, but as yet it is too soon to determine whether Britain is likely to experience a similar spike in infections driven by the new sub-variant. (Given that our population's Covid immune status is relatively high, and antibody escape with this variant so far appears to be only moderate, any such infection spike is unlikely to result in a corresponding wave of new hospital admissions.)

Whether we in UK actually see a new wave of infections resulting in more sickness is likely to depend on whether the infectivity of Arcturus is high enough to displace the already extremely infectious Omicron B series variants which are currently predominant in the UK.  

There are suggestions that the virus may have reached a peak of its potential to infect human cells, and that any further marginal increase may not necessarily lead to the new variant becoming predominant.  This is based on the assumption that selection pressure will be insufficient for it to ‘outdo’ the competition. 

How likely is it then that we will at some point see a new variant that eclipses the existing Omicron sub-variants ?  

This would probably require much more extensive changes in the viral spike protein. This would be likely to affect recognition by our existing anti-Omicron antibody and T-cell populations, and the virus may effectively 'escape' our acquired immune defences. What would be the driver for such a variant to emerge and succeed ?

We should remember that new viral variants are continually thrown up in every infection due to the inaccuracy of the viral replicase in RNA viruses. 

Such variants are most likely to be generated in subjects with chronic Covid infections due to compromised immune systems. Most of them are non-viable and go no further. Even if one of them is viable and does get passed on by an affected individual, it will only become predominant in the local population if selection pressure gives it a selective advantage over the competition.  To become predominant worldwide, it would need to maintain this advantage within other populations in order to spread; this process could fail in populations where acquired immunity levels were higher, due to higher vaccination coverage.

At present the world population still contains a large 'pool' of non-immune individuals who have neither been vaccinated nor already acquired immunity due to infection with the virus.  Given Omicron’s already high level of infectivity, a breakthrough is therefore unlikely to happen in the short term at least.  

The point at which we may begin to see new ‘escape’ variants becoming widespread is likely to come when the majority of the population have developed ‘herd immunity’ and selection pressure then starts to present these escape variants with a significant advantage over existing ones. 

If this does happen, it will of course be really bad news, since some or all of our vaccines may become ineffective at preventing serous illness. 

Although we are likely to retain at least some immunity due to antibody and T-Cell cross-reactivity, it would mean a major vaccine re-development effort, and this would be needed in a short space of time to minimise the potential death toll. Fortunately our recently acquired experience with the mRNA vaccine platforms should enable us to speed up the development and approval processes if needs be. 

It is likely that new pandemics will occur in the medium term, given population dynamics and the deterioration of healthcare.  These are likely to originate in Africa or South East Asia and may well involve Coronavirus or Influenza virus variants. Our experience with Covid should be invaluable in enabling rapid mobilisation of new vaccines.

We should, however, continue to be vigilant about Covid in the meantime, even in the absence of major viral escape. The WHO's recent downgrading of Covid's status from a world health emergency does not indicate that 'it's all over' - far from it... 

Covid is here to stay now, and definitely still able to cause us harm, particularly in the elderly and those with otherwise compromised immune systems. To minimise hospital admissions at a time when the NHS is 'teetering on the brink', a new booster campaign should be run in UK this autumn, preferably at least for everyone over 50 – so far only the over 75s and those with increased susceptibility have been eligible for the Spring campaign, which leaves the rest of the population increasingly vulnerable over the summer months. This is because more than 6 months have already elapsed since the last Autumn’s boosters were available, and we know acquired Covid immunity persists only for about 6 months. 

All the more reason, therefore, to continue taking basic precautions, particularly when out and about in public spaces over the summer months.

We should also continue to pursue development of new '2nd generation' vaccines, focusing on alternative strategies. This will provide backup in the event of future major vaccine escape by new variants (see previous blog for more detail on this.)

Watch this space for further updates…

First published 30.4.23