As winter approached the situation appeared perilous. Not only was the UK in the midst of a Covid pandemic, but experts feared familiar respiratory viruses could also hit hard.
“I will emphasise that actually flu could be potentially a bigger problem this winter than Covid,” Prof Anthony Harnden, the deputy chair of the Joint Committee on Vaccination and Immunisation, told BBC Radio 4’s Today programme in June.
The concern was that lockdown and other measures had not only reduced coronavirus infection levels, but also the global circulation of influenza. According to the Royal College of General Practitioners, the prevalence of flu in the community in England was about 95% lower in the winter of 2020-21 than normal.
The upshot, experts said, was that immunity in the population would have waned, leaving people more vulnerable to flu. And that could put further pressure on an already stretched NHS.
Nevertheless, flu has yet to deliver on the threat. According to the latest report from the UK Health Security Agency (UKHSA), “laboratory indicators suggest that influenza activity is very low,” with a similar picture seen in other metrics such as online searches for flu queries.
One important factor is that in many countries, Covid measures have remained in place over the winter, and even where restrictions have eased, behaviour has yet to fully bounce back to pre-pandemic form.
According to data from CoMix study from the London School of Hygiene and Tropical Medicine, on average adults had just below three contacts per day during December and January – compared with slightly more than 10 according to pre-pandemic surveys.
“Maybe we’ve dodged the flu for now. But we’re now waiting for its inevitable grisly return,” said Prof Sir Andrew Pollard, director of the Oxford Vaccine Group.
“The flu stayed away because global application of social distancing measures and mask wearing have been enough to keep the virus at bay.”
Another factor is that in the run-up to winter, the UK rolled out the largest flu vaccination programme in its history, with 35 million people offered the vaccine. According to latest UKHSA data, uptake among people aged 65 years and over is the highest on record at almost 82%.
While low levels of flu means vaccines have had little opportunity to have a big impact, it is reasonable to assume they may have helped prevent some sickness. But the concern remains what will happens once society begins to return to something akin to “normal”.
Pollard said: “That could mean that there is an unseasonal outbreak of flu that happens as all the social distancing and restrictions start to be released around the world if there’s enough susceptible individuals that the amount of flu can build up quite rapidly,” said Pollard, although he added outbreaks may not be seen until next winter when conditions are more favourable for its spread.”
Dr Laurence Tiley, senior lecturer in molecular virology at the University of Cambridge, also urged caution.
“The further we get into February, the more confident we can be that this season will turn out to be a good one,” he said, adding the situation seemed promising. But, he noted: “All bets are off for next season, of course.”
Tiley said that, as well as the problem of waning immunity, the low prevalence of the virus made it harder to predict the best candidate for next season’s flu vaccine.
“I think we have been extraordinarily fortunate how things have turned out this winter, with Omicron – and apparently for flu too,” he said. “Long may it remain so.”