England's September Flu Activity Beat Each of the Past Four Winters, UKHSA Says, With Levels Still at Baseline

Since flu trends began climbing in August, the UK Health Security Agency (UKHSA) has now put numbers on an early start. Its first weekly winter respiratory surveillance report, covering week 40 (Sept. 28 to Oct. 4, 2026), shows flu positivity at 6.5%, up from 5% the previous week.

UKHSA says flu activity throughout September was higher than in the same period of all four previous winter seasons. The agency also says activity is still at baseline, meaning relatively low overall.

This is a rising trend, not an outbreak.

What the surveillance data shows

According to UKHSA, several indicators point upward: the share of positive tests, GP consultations for influenza-like illness, and emergency-department attendances for influenza-like illness. Emergency attendances are above the level expected for this time of year.

The rise so far has been driven largely by 18- to 24-year-olds, UKHSA says. Both flu A subtypes, H1N1 and H3N2, are circulating in roughly equal measure.

The Daily Mail reported that the 6.5% positivity figure is almost double the 3.3% recorded at the same point last year. It also reported that Covid infections reached 4,589 in September, up from 1,374 in August, and that NHS England medical director Prof Frankie Swords warned of "ominous early signs of winter pressure ahead." Health officials stressed that both flu and Covid levels remain within the expected range, according to the same report.

Early does not necessarily mean worse

The experts quoted on this do not fully agree on what an early start signals.

Prof Antonia Ho of the University of Glasgow's Centre for Virus Research said an early rise "may indicate a more intense influenza season overall, because earlier onset is associated with a longer period of community transmission and higher cumulative case numbers." She added: "However, onset timing alone doesn't determine severity."

Prof Sir Andrew Pollard, director of the Oxford Vaccine Group, was more cautious. He said an earlier flu season did not necessarily mean a worse one. "We don't know for certain why the timing varies each year," he said. He pointed to a mix of possible factors: weather, the circulating strain and how easily it spreads, population immunity, and behaviour such as the number of close contacts people have.

The record from last winter is the one UKHSA leans on. A drifted H3N2 strain, known as subclade K, emerged after the Northern Hemisphere vaccine composition was set. The season also started early. Even so, overall activity and mortality were lower than the winter before, according to UKHSA.

The drifted strain

This year the drift is in the H1N1 virus. UKHSA cites a recent World Health Organization technical report saying one H1N1 virus seen at low levels in Europe, and recently in the UK, has changed from the component used in this year's vaccine.

UKHSA says it is too early to say whether the drifted H1N1 will spread widely in the UK or how well the vaccine will work against it. Ho made the same point.

The agency says vaccines typically still protect against severe illness when the circulating strain is not a perfect match. Its analysis from last season found vaccinated children were around 65 to 70% less likely to attend or be admitted to hospital with flu. Vaccinated adults were around 20 to 30% less likely.

The gap between children and adults is large, and adults will want to weigh it when deciding on a shot. UKHSA's modelling credits the English programme with preventing around 100,000 hospital admissions and 7,000 deaths last winter. That is a modelled estimate rather than a count of actual admissions or deaths.

Who gets a free shot, and what it costs

Free NHS flu vaccines are available only to children and higher-risk groups, Pollard noted. Others may be able to get one through an employer. Private vaccination costs about £20 at most high street pharmacies, and some retailers offer it for under £10 through membership schemes.

Pollard's advice to anyone at risk because of age or underlying health conditions is to get vaccinated as soon as possible, before transmission peaks. Both he and Ho stress timing: the vaccine takes a few weeks to give full protection, so waiting for a visible surge means being exposed during the gap.

The decision remains a personal one, and the agency's own numbers show the benefit is far larger for children than for healthy adults.

What comes next

UKHSA's week 40 report is the first of a weekly series. The next reports will show whether positivity keeps climbing from 6.5% and whether activity leaves baseline territory. They should also show whether H1N1 or H3N2 comes to dominate, and with it whether the drifted strain matters.