IT passed without much fanfare, but yesterday marked a new watershed in the UK's Covid pandemic: the official end of routine surveillance of the infection.

Since 2020, the Office for National Statistics has monitored the trends on a weekly basis using swabs gathered from thousands of participating households.

By chance, I was one of the 500,000 people randomly selected to take part.

For the first couple of years I had a monthly visit from an ONS tester, before it evolved into a postal service last year where I had to mail back a saliva sample taken during my allocated testing window.

It felt like a very small contribution to a national effort to understand how the virus was spreading and changing.

In its final update, the ONS said one in 40 people in Scotland had Covid (the trend is "uncertain") and the vast majority of UK cases (over 80 per cent) were being caused by Omicron BA.2.75 and its various sub-lineages, which include the XBB strains.

One of these, XBB.1.5 (nicknamed 'Kraken' by social media users) has been rising steeply since January and is probably now responsible for around half of infections.

The Herald: Tweet from Professor of Evolutionary Biology, Ryan Gregory, showing growth in XBB.1.5 in UK since January based on sequenced casesTweet from Professor of Evolutionary Biology, Ryan Gregory, showing growth in XBB.1.5 in UK since January based on sequenced cases (Image: Twitter/@TRyanGregory)

It has been designated as a Variant of Interest (VoI) by the World Health Organisation due to evidence of increased transmissibility and immune-evasion, although the agency cautioned that there are "no early signals of changes or increases in severity".

However, it also added that a full assessment is hindered by the "limited data currently available globally".

READ MORE: How well do Covid infections protect against future illness? 

The end of mass surveillance in the UK - until now, a world-leader in Covid genomic sequencing - will add to the problem as, globally, we become less able to track or identify potentially worrisome variants at an early stage.

The winding up of the ONS household survey has provoked a mixed response from scientists.

Some acknowledge that the cost - £945 million as of December last year - was unsustainable, and that monitoring is not carried on such a scale for other common viruses such as influenza.

It also comes as the UK prepares to rollout another round of Covid boosters to the most vulnerable, including elderly care home residents, over-75s, and people with weakened immune systems.

Others would have preferred to see the survey scaled-down, rather than discontinued.

"There is a case to be made for it continuing, just because it might identify something we really weren’t expecting," said Thomas House, a professor of mathematical statistics at Manchester University.

The Herald: Covid testing is continuing only in a minority of settings, such as managing high risk patients in hospital or for people who may require antiviralsCovid testing is continuing only in a minority of settings, such as managing high risk patients in hospital or for people who may require antivirals (Image: Getty)

Professor Christina Pagel, a healthcare scientist and member of the Independent SAGE expert group, said the ONS survey had been the "gold standard measure of Covid prevalence"

She added: "We should be diversifying this unique infrastructure and population group to other infections and public health priorities, not dismantling it...It will make understanding what is happening with Covid much harder.

"Plus, with H5N1 on the horizon, don't we want to stay prepared?"

READ MORE: Never had Covid? Why the secret might lie in your genes 

For its part, the ONS says the programme is "paused" as surveillance is "balanced alongside emerging healthcare priorities", but could resume if necessary.

It also hasn't ruled out the possibility of using the resource to monitor other respiratory infections.

So what of our future pandemic preparedness?

This time three years ago we were just nine days into the first Covid lockdown after a faltering response on everything from border controls to mass testing left the novel coronavirus to sweep through the population.

It was a case of shutting the stable door after the proverbial horse had bolted - a way of buying time and "flattening the curve" in terms of hospital admissions.

Looking ahead, scientists want to be in a position to detect and stop 'Disease X' before it can become a pandemic.

This is the term used to describe a pathogen with "epidemic potential" that is yet to appear.

It could be a virus, fungus, or bacterium. It could spillover from animals into humans, or spring up as a result of a mutation - turning a disease that had been under control into something suddenly dangerous.

The rise antibiotic-resistant microbes is one such threat.

Recently, attention has focused on a mutated strain of H5N1 avian influenza, which has killed record numbers of seabirds in Scotland and begun spreading in parts of the world (such as South America) where it has not previously been found.

Infections have spilled from birds to animals, including otters, seals, sea lions, and foxes.

The Herald: Millions of birds around the world have died in the current H5N1 outbreakMillions of birds around the world have died in the current H5N1 outbreak (Image: PA)

A technical briefing published by the UK Health Security Agency on Wednesday said there is evidence of "limited mammal to mammal" transmission, including between farmed mink, but the risk to humans is considered low.

Since December 2021 there have been eight human cases reported worldwide, including one this week in a 53-year-old man in Chile.

Vaccine makers have been preparing bird flu shots for humans "just in case" and the UKHSA has drawn up contingency plans based on case-fatality ratios (CFR) - the number of deaths per 100 infections - ranging from 0.25% (similar to Covid in autumn 2021) to 5%, in line with the original 2002 SARS virus.

READ MORE: What was behind the child hepatitis outbreak? Scientists reveal 'convincing evidence' for an unexpected cause

These are modelling exercises, rather than predictions.

In reality we have no idea how deadly H5N1 would be if it suddenly developed sustained human-to-human transmission.

Estimates based on the percentage of humans who have died after contracting the virus from birds - around 50-60% - may be terrifying, but they are also probably wide of the mark based on previous flu pandemics (the CFR for the 1918 Spanish flu, for example, is estimated to have been 2-3%).

In Oslo, the Coalition for Epidemic Preparedness Innovations (Cepi) wants the world to be able to respond to the next Disease X with a new vaccine in 100 days, using a bank of "prototype vaccines" that are essentially ready-to-go against hundreds of viruses we already know about.

New vaccine technologies, such as mRNA, make development much quicker - even against novel viruses.

It can't work for all cases (HIV continues to defy a vaccine solution), and bacterial or fungal outbreaks would pose a different challenge - not to mention the logistical challenges of accelerating clinical trials and manufacturing capacity.

But if the 100-day rule had applied to Covid, we would have been queueing up for vaccines by March 2020 instead of locked down in our homes.