The UK Health Security Agency (UKHSA) has released its inaugural weekly winter respiratory virus surveillance report, drawing on a comprehensive array of indicators from general practitioners, hospitals, laboratories, and the wider community.
Flu Activity on the Rise
The surveillance report for week 40, covering the period from 28 September to 4 October 2026, indicates a notable increase in influenza activity, which is now circulating at baseline levels. The report highlights a rise in flu positivity, climbing to 6.5% compared to 5% in the previous week. Overall, flu-related hospitalisations have reached 1.97 per 100,000, although as this surveillance officially commenced in week 40, comparisons to earlier weeks are not feasible.
Flu activity throughout September has surpassed levels observed during the same period in the past four winter seasons. While still classified as very low, flu trends have been on the upswing since August, suggesting the potential for an early onset of flu season.
Demographics and Other Respiratory Viruses
The report further reveals that the rise in flu cases is predominantly driven by young adults. Additionally, COVID-19 activity has also begun to increase, though it remains at low levels. The strains currently circulating, including those identified as XFG, are closely related to variants that have been prevalent for over a year. Meanwhile, activity related to the rhinovirus, commonly associated with the common cold, is now beginning to decline following a sharp increase in recent weeks. The Respiratory Syncytial Virus (RSV) continues to circulate at baseline levels, with minimal activity noted.
The Importance of Annual Flu Vaccines
Flu viruses exhibit annual variations, necessitating updates to flu vaccines each year. Occasionally, ‘drifted’ flu viruses emerge, indicating that the circulating strain has undergone genetic changes compared to the version used to formulate the vaccine. A recent report from the World Health Organization (WHO) indicated that a flu A(H1N1) strain recently observed in low levels across Europe, including the UK, has ‘drifted’ from the strain included in this year’s vaccine. Last year, a similar drift was noted with the A(H3N2) strain, yet the vaccines still provided robust protection.
At this stage of the season, it remains too early to determine with certainty whether this drifted A(H1N1) virus will become widely prevalent in the UK or the vaccine’s efficacy against it. So far, the subtyping data indicates an equal mix of A(H3N2) and A(H1N1) subtypes circulating in England.
Understanding Vaccine Composition and Effectiveness
It is crucial to note that the flu vaccine is designed to protect against all three types of flu viruses, including Flu A subtypes H1N1 and H3N2, and Flu B. As flu seasons can be unpredictable, certain years may see one strain dominate while in others, all three types may circulate at varying times throughout winter. Historical data, such as the A(H3N2) strain that dominated last year, indicates that flu vaccines generally remain effective in preventing severe illness, even against drifted strains.
Despite the emergence of drifted viruses and an earlier start to the flu season last year, overall case levels and mortality estimates throughout the season were lower than in the previous year. Modelling suggests that the vaccination programme in England last winter prevented approximately 100,000 hospital admissions and around 7,000 deaths.
Expert Insights and Recommendations
The composition of flu vaccines is adjusted annually by the WHO to accommodate genetic changes and to provide protection against the most likely circulating viruses. Decisions regarding which strains to include are made several months prior to the onset of flu season, allowing manufacturers to prepare adequate stocks. However, as viruses continue to evolve, there can be discrepancies between the vaccine and the strains that emerge once vaccines are delivered.
Dr Jamie Lopez-Bernal, Consultant Epidemiologist at UKHSA, emphasised the importance of vaccination amid rising flu levels and the potential for an early flu season, urging those eligible to get vaccinated. The flu vaccine includes components to protect against all three types of flu viruses, and it is anticipated that one strain may dominate at various times throughout winter.
COVID-19 Surveillance and Public Health Guidance
The report on COVID-19 for week 40 indicates that activity has increased, yet remains at low levels. The positivity rate has risen to 9.1%, up from 7.9% the previous week. COVID-19 hospitalisations have also increased to 2.04 per 100,000, compared to 1.75 the week before, while ICU admissions remain low at 0.06 per 100,000.
Dr Alex Allen, Consultant Epidemiologist at UKHSA, noted that while there has been a slight uptick in COVID-19 cases, they remain relatively low across the UK. He highlighted that the circulating strains, including those labelled as XFG, are largely similar to those observed over the past year, with no current evidence suggesting they are causing more severe illness or spreading more rapidly. The autumn vaccine has been tailored to protect against these strains.
For individuals eligible for a free vaccine, appointments can be booked through the NHS app, online, or by contacting local GP practices or pharmacies. Detailed information regarding vaccine eligibility is available on the UKHSA blog, providing guidance on who qualifies for both the flu and COVID-19 vaccines.