Why the UK could be heading for a flu-covid ‘twindemic’ this winter

Last year’s warnings about a particularly bad flu season didn’t materialise, but an earlier and more severe outbreak in Australia doesn’t bode well for the northern hemisphere

By Clare Wilson

Along with several other countries, the UK is stepping up its efforts to persuade at-risk groups, including anyone aged 50 and over, to get vaccinated against both flu and covid-19 in the coming weeks.

Today, the UK Health Security Agency (UKHSA) launched its autumn vaccination campaign for these diseases, warning that this winter is likely to be particularly bad for flu.

At this point, some people may be experiencing déjà vu. There were similar claims 12 months ago, but the expected “twindemic” of flu and covid-19 didn’t materialise.

But that doesn’t mean we should disbelieve the warnings this time around. Last winter, many people were still practising social distancing, to greater or lesser extents.

In England, as the omicron coronavirus variant began surging in December 2021, “Plan B” rules were introduced, including compulsory face masks in most indoor public spaces and proof of vaccination to enter venues such as nightclubs.

There was also less social mixing in other ways, such as more widespread working from home.

In the end, this couldn’t hold back the omicron surge, but flu is less transmissible than the coronavirus and it was suppressed to very low levels.

The number of people hospitalised with flu in England peaked at one-sixth of the number seen the year before the covid-19 pandemic took hold.

In an average winter, 20 to 30 per cent of people are exposed to the flu virus, although many have no symptoms. This means that for two years running, nearly all those normal exposures didn’t happen. As this winter approaches in the UK, there will be much less population immunity to flu than normal.

This winter, social mixing is likely to be back to pre-pandemic levels as the UK has announced no plans for reintroducing restrictions. The coming flu season therefore looks set to be the first in three years that will allow the usual levels of respiratory virus spread.

Australia’s experience over the past few months, during its winter, provides an indicator of what may happen in the northern hemisphere. Cases peaked significantly higher there than in the three years before the covid-19 pandemic began.

The main flu variant in Australia this year was called H3N2, which past research suggests causes more severe illness than typical seasonal flu. This strain was linked with a somewhat higher flu hospitalisation rate in the UK six years ago.

Fortunately, the flu vaccine soon to be on offer in the northern hemisphere contains the H3N2 virus, in an inactivated form.

The Australian flu season this year not only saw a higher peak of cases than average, but these also happened earlier in its winter, surging in May and June rather than July and August.

For this reason, it is important that anyone in the northern hemisphere who is eligible gets vaccinated against flu as soon as they can, says the UKHSA. “You should book in as soon as possible,” Steve Russell, National Health Service England director for vaccinations and screening, said in a statement.

Covid-19 also hasn’t gone away. The latest figures from hospitals and the Office for National Statistics show that cases are starting to rise again in the UK.

“This winter could be the first time we see the effects of the so-called twindemic, with both covid and flu in full circulation,” said Russell.

The good news is that the rise in covid-19 isn’t being caused by a radically different coronavirus variant, but by several new subvariants of omicron – and the bivalent vaccine on offer in many countries contains an omicron component. In the UK, everyone eligible for a booster should be offered the bivalent version, barring supply disruptions.

The twin threat makes it all the more important that eligible groups take up their offers of covid-19 boosters and flu vaccines, says Simon Williams at Swansea University, UK.

“Public health campaigns need to provide clear and strong messages about the risks of flu as well as covid to those who are vulnerable as well as to the health system – akin to the ‘Protect the NHS’ campaign which worked so well earlier with covid,” says Williams.