The numbers that suggest a new Covid wave is already gripping the UK

 

Ever since the highly contagious Stratus Covid variant starting spreading rapidly in the UK in April, scientists have feared a new wave.

But while Stratus has spread rapidly to become the country’s dominant Covid variant, the overall infection rate did not take off as predicted – which is not to say there wasn’t a clear increase in numbers, just a much smaller one than many had feared.

This is because, to a large extent, the Stratus variant – formally known as XFG – was supplanting the other variants (keeping overall Covid cases more or less steady when they may overwise have fallen), rather than sending them soaring.

The latest data from the UK Health Security Agency (UKHSA) suggests that may be changing and that a long-anticipated “summer” wave could finally be upon us.

The data shows that the proportion of hospital patients with respiratory symptoms testing positive for Covid jumped by 22 per cent in just over a week, from 7.2 per cent on 6 August to 8.8 per cent on Friday 15 August.

In less than three weeks, the increase in positive hospitals tests had risen to 44 per cent by 15 August.

As such, the figure (known as the positivity rate) is now four times as high as it was in early January. However, it is still less than half what it was at last year’s peak, in July.

With children set to go back to school – in many cases after international travel, which can turbocharge virus circulation – there are fears that the recent rises could continue and we could find ourselves in a new wave – a period of increased transmission of the virus – if we are not already in it.

Cooling weather will add further pressure as people spend more time indoors, often in poorly-ventilated rooms.

It is important to stress that, because the numbers are based on hospital patients with respiratory symptoms, the resulting Covid positivity rate is much higher than for the public as a whole.

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But in the absence of population wide surveillance, which does not happen in the summer, the UKHSA statistics are the best indicator of trends that we have, scientists say.

“Test positivity rates, while not directly estimating the number of Covid infections in the general population, can be a valuable indicator of the infection trend,” says Bob Hawkins, a data scientist who works with Independent Sage.

His analysis has shown that the UKHSA positivity data and winter surveillance data for the general public show similar trends – indicating that the positivity rate is a reliable, if rough, sign to what is happening more widely.

Scientists say waning immunity from vaccines and previous infections is a key reason for the recent rise in infections.

At the same time, the XFG variant is more contagious than the other variants and may be better at evading vaccines designed for earlier variants (although the latest version of the vaccine is still considered to offer good protection – especially against serious illness).

Against this backdrop, there are some concerns that the Government’s decision to offer the autumn booster to 13 million fewer people this year including pregnant women and heart disease patients, could push up cases further.

The decision is based on expert advice from the Joint Committee on Vaccination and Immunisation (JCVI) which continuously monitors and evaluates emerging scientific evidence on Covid vaccines but, there are plenty of scientists who think it is a bad idea.

So if we are not already in the grip of a new Covid wave, the data for the last few weeks combined with waning immunity, “back to school” traffic and cooling weather strongly suggests we may soon be.