IF the Covid pandemic has felt like a horror film at times, the endless proliferation of new Omicron sub-lineages is starting to resemble a franchise of tedious straight-to-video sequels.

For many people, signs that the BA.4 and BA.5 strains have probably replaced BA.2 as the dominant strain in the UK and are now setting in motion a summer Covid wave - our sixth to date - might be met with a weary sigh.

Afterall, Halloween 6:the Curse of Michael Myers was never going to have the same shock value as the original.

READ MORE: One in 30 Scots infected as BA.4 and BA.5 on the rise

Nonetheless, clinicians are rightly concerned about the potential impact any rise in Covid cases and an accompanying increase in admissions will have on the NHS, given all the requirements for isolation and the loss of beds that entails at a time when demand is already far outstripping supply.

There is at least some hope that pre-existing immunity and warmer summer weather could blunt the BA.4/5 wave.

A much bigger threat is starting to loom on the horizon, however, in the form of an influenza resurgence and the potential for a double whammy of Covid and flu this winter - something we have dodged for the past two years.

In Australia, influenza-like illness has been increasing in the community since March and now exceeds the average for the time of year.

The country's public health authorities are growing concerned that the country could be heading for one of its worst ever flu seasons after a record 65,770 influenza cases were confirmed in May - more than double the previous May record set in 2019.

By June 5, Australia's national disease surveillance system had reported a further 88,000 flu cases (though many had been diagnosed in May).

HeraldScotland: Flu cases began rising rapidly in Australia in AprilFlu cases began rising rapidly in Australia in April

There have been 27 flu-related deaths in the year to date and more than 730 people have been admitted to hospital in Australia due to influenza since April, of whom around 44 went straight into intensive care.

Data this week from the state of South Australia also shows that the average age of flu cases in that region is 18, indicating that half of all infections are occurring in children.

Speaking to ABC Radio Adelaide, Rod Pearce, chair of the Immunisation Coalition, said: "We've got a population that hasn't seen influenza for a couple of years so it's going to hit us quicker.

"There are children who've never seen flu because they're born after the last [flu] season."

HeraldScotland: Data from South Australia shows cases on the riseData from South Australia shows cases on the rise

There is now a push for more young Australians to get vaccinated against flu in bid to curtail overall virus spread.

Health Minister Chris Picton said: "That increased number of flu cases is having an impact on hospitals that are already overwhelmed with Covid cases and other respiratory conditions

"We do want to see more and more younger South Australians come forward and get protected for the free flu vaccine because we know that the number of cases that we're seeing in younger people are quite significant."

READ MORE: Almost no flu cases in Scotland for second year in a row

Australia isn't always an accurate bellwether for the subsequent influenza season in the northern hemisphere, but Dr Jonathan Anderson from pharmaceutical company Seqirus - which specialises in influenza vaccines - said the rest of the world will be "watching closely" as they draw up their own plans.

“Australia is in a unique position in that we are one of the first countries to face Covid and a simultaneous flu season that is similar to pre-Covid levels,” he said.

Given the substantial strain already on the NHS, with A&E staff battling "winter-like" conditions non-stop now for the past 12 months and spiralling backlogs for elective care, it seems increasingly likely that public health bodies in the UK will recommend offering Covid and flu boosters to everyone before this winter hits.

HeraldScotland: Scotland had its worst flu season in seven years in 2017/18Scotland had its worst flu season in seven years in 2017/18

HeraldScotland: Flu in Scotland all but vanished over the past two years (Source: Public Health Scotland)Flu in Scotland all but vanished over the past two years (Source: Public Health Scotland)

Six months from now, BA.4 and BA.5 will probably have been replaced by yet another new variant, which we can only hope is less virulent - though that is not guaranteed.

Maria Van Kerkhove, Covid-19 technical lead for the WHO, warned this week that nations are "really playing with fire" by increasingly scrapping testing, sequencing and basic public health measures, given that the virus "continues to evolve".

READ MORE: Experts back Covid boosters for all amid warning 'quite a surge' in infections looms

The emergence of a vaccine-resistant or more virulent strain in combination with a flu resurgence really would be the stuff of nightmares for the NHS.

Scotland's last really bad flu season was in 2017/18 - the same winter when deaths hit an 18-year high of 23,137.

HeraldScotland: Winter deaths have been falling steadily in Scotland since the 1950s, but recent years point to an increasing trend (Source: National Records of Scotland)Winter deaths have been falling steadily in Scotland since the 1950s, but recent years point to an increasing trend (Source: National Records of Scotland)

The main underlying cause of the deaths were influenza and pneumonia, a situation possibly exacerbated by shortages of the aTiv vaccine given to the over 75s.

This was only exceeded in the first winter after Covid, when there were 23,370 deaths between December 2020 and March 2021.

However, "excess winter mortality" was actually worse in 2017/18 than in 2020/21.

The difference between the number of deaths which occur during winter compared to the periods before and after (that is August-November and April-July) is used to gauge the seasonal spike.

HeraldScotland:

 

HeraldScotland: Source: NRS Winter Mortality in ScotlandSource: NRS Winter Mortality in Scotland

In 2017/18, there were 4,797 "additional" deaths in winter, compared to 4,330 in the 2020/21 winter when the Alpha Covid strain took off.

Of course, mortality was partly kept at bay by severe the Covid restrictions implemented just before Christmas 2020 and which extended until April the following year; had coronavirus been left to spread unhindered (as flu generally is), then the excess winter death toll would have been much higher.

A lot has been made of how a combination of vaccinations, natural immunity, and Omicron (which is less virulent than Delta or Alpha, but roughly on a par with the original Wuhan strain) means that Covid is now less deadly than flu, even among the over-80s.

But that becomes less reassuring when you consider that a bad flu season can overload the NHS.

Add to that Covid rates which have yet to dip below one in 50 this year - even in summer - and winter number three in the pandemic trilogy could turn out to be very bad indeed.