• Seasonal influenza occurs every year, is a key driver for winter pressure on the NHS and a leading cause of excess deaths every winter.
  • The influenza season, together with other respiratory infections, is likely to coincide with COVID-19 this winter.
  • It is not possible to predict the severity of the influenza season this winter or how the transmission of SARS-CoV-2 might change in colder weather. Those most at risk from influenza are also most vulnerable to COVID-19. Children play a key role in influenza transmission. These groups are offered the influenza vaccine.
  • Influenza and COVID-19 share some symptoms which will make diagnosis challenging. Influenza cases are likely to put pressure on COVID-19 test, trace and isolate systems.
  • Immunisation against influenza virus is an effective intervention but the extent to which it reduces transmission, cases and NHS demand is determined by vaccine availability and effectiveness, how many people are immunised, and the timing of the immunisation within the influenza season.
  • This year’s national influenza immunisation programme will be expanded to include a much wider proportion of the population.
  • Influenza vaccine coverage varies widely between eligible groups. People aged under 65 years with health conditions, and pregnant women are at risk but immunisation coverage in these groups is consistently below 50%. Achieving the target coverage of 75% will require a significant effort across the NHS in challenging circumstances.
  • Immunisation clinics will need to adapt to meet social distancing requirements.
  • It is likely that international demand for influenza vaccines and antiviral drugs will outstrip supply. The UK Government has stated that it has secured additional national supplies.
  • This is part of our rapid response content on COVID-19.  The article will be updated as the research progresses. You can view all our reporting on this topic under COVID-19.

Seasonal influenza is a recurring risk that puts winter pressure on the NHS. The extent of this pressure results from several factors. This winter it may coincide with ongoing and possible increased transmission of SARS-CoV-2 that causes COVID-19. The annual influenza immunisation programme, which reduces the transmission of the virus, and decreases the number of cases, hospitalisations and influenza-related mortality will, therefore, be of even more importance this winter. This has been recognised by experts and by Government, which has announced an expansion of the national influenza immunisation programme for 2020–2021. This article summarises the impact of influenza on the NHS in the context of COVID-19, the role of immunisation, changes to the influenza immunisation programme later this year and the challenges for the NHS this winter.

Influenza surveillance, reporting and immunisation coverage data are collected and published by Public Health EnglandPublic Health Agency Northern IrelandHealth Protection Scotland, and Public Health Wales. All four nations follow the advice from the Joint Committee on Vaccination and Immunisation on which vaccine to use and who to vaccinate. There are some operational differences between immunisation services.

The impact of influenza

Influenza is just one of the challenges that will impact demand on the NHS this winter. A report on preparing for winter challenges was published by the Academy of Medical Sciences; this was considered by the Scientific Advisory Group for Emergencies (SAGE) at its meeting on 9 July. SAGE had previously advised the UK Government of the importance of an expanded winter influenza immunisation programme in April.

Influenza is a common infection and mild for most people. However, it can be very dangerous for vulnerable people, including older adults, pregnant women and people with underlying health conditions, for whom infection can result in hospitalisation and death. Influenza has a high impact on the NHS through increased demand on primary (GP consultations) and secondary health care services (hospitalisations and intensive care bed admissions). In winter 2017–2018, influenza levels were high and this led to deferral of all elective inpatient and outpatient NHS care in England throughout January.

The impact of influenza on population health and pressure on the NHS varies each year because it depends on several factors: which strains of the virus are circulating and who is most likely to be affected, how effective the annual vaccine is, how many people are immunised, and winter temperatures. Most cases of influenza occur between December and March and immunisation is delivered from October to the end of February.

Seasonality of influenza and coronaviruses

Influenza shows seasonality because it is more common in winter. This results from the interaction of several biological, environmental and behavioural factors. Temperature and humidity can affect the virus’s stability; it survives better and transmits more easily in cooler, drier air. The immune response to viral infections can be weaker in winter as a result of less exposure to sunlight. Transmission of respiratory viruses is also higher in winter because people are more likely to spend time together indoors.

It is not yet clear whether the SARS-CoV-2 virus will show a seasonal effect in the same way as influenza virus. SARS-CoV-2 is transmitted through direct or indirect contact with droplets, as are the four other coronaviruses that cause the ‘common cold’ in the community (229E [alpha coronavirus], NL63 [alpha coronavirus], OC43 [beta coronavirus] and HKU1 [beta coronavirus]). These have been circulating for years and tend to spread in winter, like influenza virus, often at the same time. It is not clear if immunity to these coronaviruses will offer any protection against SARS-CoV-2 and, if so, how long it might last.

Modelling data suggest that COVID-19 outbreaks that happen in late winter or spring are likely to be less severe than those at other times of the year. Researchers are also looking at patterns of COVID-19 disease in the southern hemisphere and examining any associations with temperature, rainfall, humidity and other environmental variables. One study compared 50 cities with and without transmission of COVID-19 in March. It found that cities with severe COVID-19 outbreaks in late winter 2020 were in a narrow band of latitude (30–50 degrees north) and have similar winter climates.

Interaction between SARS-CoV-2 and other respiratory viruses

The other common respiratory viruses that circulate in winter are respiratory syncytial virus, other coronaviruses and rhinoviruses. There are no licensed vaccines for these viruses.

Sometimes when different viruses are circulating at the same time, their transmission can be affected by positive or negative interactions between them. Sometimes an initial infection can cause subsequent infections to be more severe. In other cases the immune response to an infection can offer short-lived protection against other viruses.

It is not clear what the viral interactions between SARS-CoV-2, influenza virus and other respiratory pathogens will be and if co-infections will occur or not. However scientists speculate that co-infection of SARS-CoV-2 with other respiratory or gastrointestinal infections may lead to an increased risk of transmission. This risk can be mitigated through social distancing and hand hygiene.

The UK was at the end of last winter’s influenza season when COVID-19 cases peaked. Some unpublished data from Public Health England on 65 patients that had both COVID-19 and influenza found that they were more likely to die than those who had COVID-19 alone.

Influenza deaths in the UK

The Office for National Statistics publishes data on the causes and number of deaths in the UK and Public Health England publishes annual reports on influenza. An important measure used in ONS analysis is excess mortality – this refers to additional deaths in a given time period compared with the number that would be expected. Respiratory infections, including influenza, are consistently the leading cause of excess deaths in winter, with influenza usually accounting for about one-third of deaths. The table below outlines key data on excess deaths from previous winters. In winter 2018–19 there were 23,200 excess winter deaths that coincided with milder winter temperatures and low to moderate levels of influenza. This was the lowest level of excess deaths seen in winter since 2013–2014. The overall effectiveness of the vaccine for 2018–2019 was 44.3% and was most effective in those aged over 65 (49.9%). The data for winter 2019–2020 is not yet complete, but influenza activity was low, temperatures were relatively mild, vaccine effectiveness was almost 50% and an estimated 8,000 excess winter deaths were attributed to influenza.

Vaccine effectiveness is calculated by working out how well the vaccine protects people against becoming ill with influenza. This is typically done by comparing whether vaccinated people presenting with an influenza-like illness are more likely to test negative for the virus than those who have not had the vaccine.

Peaks in excess winter deaths, a significant proportion of which were associated with influenza occurred in 2014–2015 and 2017–2018, which were colder on average and when vaccine effectiveness was low. The effectiveness of the vaccine is a key factor. Higher effectiveness is seen when the strains in the vaccine match those circulating in the population.

Year Excess deaths (influenza-related estimate*) Average winter temperature Influenza activity Predominant influenza strain and main affected group Overall vaccine effectiveness
2013–2014 17,310 (*) 6.2°C Low A(H1N1); young adults 61%
2014–2015 43,850 (28,330) 4.8°C Moderate A(H3N2); elderly 34%
2015–2016 24,580 (7,371) 6.2°C Moderate A(H1N1); young adults and children 52.4%
2016–2017 34,530 (15,047) 6.0°C Moderate A(H3N2); elderly 39.8%
2017–2018 50,100 (22,087) 4.3°C Moderate to high A(H3N2) and B; elderly 15% (10.1% in over 65s and 26.9% in children)
2018–2019 23,200 (3,966) 5.2°C Low to moderate A(H1N1) and A(H3N2); younger adults 44.3%
2019–2020 * (7,990**) 5.3°C Low A(H3N2); elderly 42.7%
Table 1. Key data on excess winter mortality, winter temperatures, influenza activity and vaccine effectiveness (2013–2020). Source: Public Health England.  *data not available **Influenza season up to week 9 of 2020 (1 week before the first COVID-19 death in the UK) 

Immunisation against influenza

There are three subtypes of influenza A, B and C, but nearly all illness is caused by A and B. Vaccines usually contain a mixture of 3–4 strains from the A and B subtypes. The vaccine cannot cause influenza illness.

The annual influenza immunisation programme is delivered to protect those most at risk from influenza and is the most important public health intervention to reduce NHS winter pressure. Immunisation is needed annually because the virus evolves and the relative proportions of different strains of the virus circulating in the population can change over time. The immune response to influenza viruses is also short-lived. Therefore the vaccine used in the annual immunisation programme is designed to align with the strains of the virus that are most likely to be circulating. The World Health Organization recommends the composition of vaccines to use in the Northern Hemisphere in February for use the following winter. It takes about 6–8 months to manufacture, approve and distribute the vaccine.

Where can people get influenza vaccines?

Young children (2–3 years old) are vaccinated at GP practices while older children aged 4–11 years receive the vaccine at school. Adults in eligible groups receive the vaccine in GP practices, in hospital settings, occupational health services, care homes or in community pharmacies. The vaccine is also available privately with some employers buying vaccine for their workforce. Individuals can also buy a vaccine from a pharmacy or other private vaccine provider.

Who is eligible for influenza immunisation this winter?

The influenza immunisation programme will be expanded this year by offering the free vaccine to more people, including children who are in their first year of secondary school. In total, 15,344,033 people received the vaccine in 2019–2020. The Department of Health and Social Care has announced that it intends to double the number of people being immunised this winter. This is to reduce the number of influenza infections and therefore reduce the pressure on the NHS this winter.

The vaccine is offered to people in at-risk groups. These people are also those at most risk from COVID-19. The vaccine is also given to children, not only to protect them individually but to prevent the spread of influenza. This offers indirect population to other people who are not immunised (for example infants under 6 months old) or who produce a weaker immune response to the vaccine (the elderly). The groups eligible for influenza immunisation this winter are:

  • Children aged 2 to 11 (children aged 2–3 receive immunisation via GP practices, all other children are vaccinated at school).
  • Over 65s.
  • People aged 6 months to 65 years in clinical risk groups.
  • People on the NHS Shielded Patient list for COVID-19 and members of their household.
  • Pregnant women.
  • Care home residents.
  • Close contacts of immunocompromised individuals.
  • Health and social care staff.
  • 50–64 year olds (this group will be invited to have the vaccine later in the season). In Scotland this group includes 55–64 year olds, but could be extended to 50–54 year olds subject to vaccine supply.

Effectiveness of the influenza immunisation programme

The effectiveness of the programme depends on several factors. Winter weather is an important factor but the relationship between winter temperature, viral transmission and influenza cases is not straightforward. Influenza strains used in annual vaccines are selected in advance of the influenza season and in some cases the strains circulating in the population do not match those used in the vaccine. Most vaccines used in the UK programme contain three or four influenza strains and are recommended by the Joint Committee on Vaccination and Immunisation, a government advisory group. Data on vaccine effectiveness in previous years shown in Table 1 indicate that the maximum overall effectiveness is unlikely to exceed 60%, but the level of protection can vary significantly between age groups.

Factors that can be directly managed by governments are the availability of vaccine, timing of immunisation and approaches that maximise vaccine take up by eligible groups. Overall effectiveness is influenced by all these factors.


The timing of the vaccine is important so that people are protected before influenza virus starts circulating. It takes about 2 weeks to generate an immune response to the vaccine. The programme usually begins in September and continues until February. Influenza virus circulates between October and March, with peaks typically occurring between December and February.


Table 2 below gives data on the proportion of people in each eligible group who were immunised in England. Coverage is the highest in adults aged over 65 years and healthcare workers with about three-quarters of people immunised. Last winter, 60.4% of children in primary school were immunised. Less than half of people in other groups were immunised, with little year on year increase in coverage. The target coverage set by NHS England for 2019 was 75% of eligible adults, an interim target of 55% for people in clinical risk groups, 50% for 2 and 3 year old children and an average of 65% coverage by every provider delivering immunisation in primary schools in England. Sufficient coverage is necessary to generate herd immunity.

New targets have been set this year with an aim for minimum 75% coverage in all groups.

  2019–2020 2018–2019 2017–2018 2016–2017
Over 65s 72.4% 72% 72.6% 70.5%
Healthcare workers 74.3% 70.3% 68.7% 63.2%
People in clinical risk groups (6 months to under 65 years) 74.3% 48% 48.9% 48.6%
Pregnant women 43.7% 45.2% 47.2% 44.9%
Children (2–3 year olds)* 43.8% 44.9% 43.5% 38.1%
Children (primary school age**) 60.4% 60.8% 59.5% 55.4%
Table 2. Seasonal influenza vaccine coverage in different groups eligible for immunisation in England. Source: Public Health England *2 and 3 year olds are offered immunisation at GP practices (in 2016–2017, 4 year olds were offered vaccination in GP practices). **The influenza programme for primary school aged children has expanded to include more year groups since it began in 2013–2014, and in some years also included pilot groups of children from older age groups: 2016–2017 (5–8 year olds); 2017–2018 (4–9 year olds); 2018–2019 (4–10 year olds); 2019–2020 (4–11 year olds). 


In 2012 the Joint Committee on Vaccination and Immunisation recommended that the influenza immunisation programme be extended to include children aged between 2 and 17 years. This is to protect children from influenza, but the other key objective of the childhood programme is to offer indirect protection to vulnerable people by preventing transmission in the wider population. This is because children are the main transmitters of influenza. The vaccine used in children is a nasal spray not an injection.

NHS England has written to those responsible for delivering childhood immunisations setting out the need for timely ordering of adequate vaccine supplies and that all local immunisation teams should have delivered the school programme by 15 December 2020. The previous target for Local Authorities (LAs) in England was that 65% of eligible children are immunised; of 152 LAs in England, 59 achieved this target last year. In 2019–2020, 60.4% of school age children were immunised (60.8% in the previous year). There are some differences in coverage across the UK. Coverage was higher in Northern Ireland (75.4%), Scotland (71.3%) and Wales (69.9%). Children in at-risk groups can have the vaccine from their GP instead of waiting for the session offered in their school. Pre-school children receive the vaccine at GP practices, and the coverage is consistently much lower in this age group compared with older children vaccinated at school. The target for coverage this year is 75%.

Drug treatments for influenza

Antiviral drugs are recommended by the National Institute for Health and Care Excellence (NICE) to treat people in high-risk groups who have influenza. This is because there is some evidence that, if given early, drugs can reduce the risk of death for people hospitalised with influenza. The drugs can also be used as a prophylactic in people in an at-risk group who have been exposed to the virus to reduce the risk of developing influenza.

Key challenges in minimising the impact of influenza this winter

Forecasting the impact of influenza

The impact of influenza this winter is uncertain but even moderate influenza activity is likely to cause substantial NHS pressure as seen in previous winters. It is not possible to predict with accuracy which influenza strains will circulate in any given season or how effective this year’s vaccine will be.

Winter weather is an important factor but the relationship between temperature, humidity and viral transmission is not straightforward.

The Met Office provides an outlook for winter weather for Government that highlights the possible implications for a range of outcomes such as flooding, demand on energy supplies and health impacts. Based on current signals, it is probable that the full winter season is likely to be milder than usual overall, but less so than last year’s very mild winter. There remains a chance of a cold winter with spells of low temperatures. Indications for late autumn and the start of winter suggest that prolonged low temperatures are somewhat less likely than usual during October, November and December 2020. Prolonged low temperatures are more likely to occur between January and March 2021 than between September and December 2020.

It is possible that the prevention measures in place to limit SARS-CoV-2 transmission (hand hygiene and social distancing) will also reduce transmission of influenza. This effect has been seen in Australia this year, where influenza activity is lower than average so far.

Pressure on testing services

One of the challenges for the healthcare system is that influenza and COVID-19 can produce similar symptoms, notably fever and cough. This will make it challenging for healthcare professionals to determine whether patients reporting similar symptoms have influenza, COVID-19 or other respiratory illnesses that are common in winter. An increase in respiratory illnesses including influenza occurs every winter, so it is likely the demand on the COVID-19 test, trace and isolate programmes will increase. Improved rapid point-of-care diagnostics will be important. Tests that deliver results in about 30 minutes already exist for influenza virus and some other respiratory viruses. Similar rapid tests that also detect SARS-CoV-2 are on the market, with the UK Government announcing purchase agreements for two tests that give results in 90 minutes. The scale of the test and trace programme will need to accommodate the expected increase in demand this winter.

Promoting influenza immunisation

Public information campaigns are used to promote uptake of the influenza vaccine. Scientists on the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) that advises the UK Government has recommended, as a high priority, that at-risk people should be made aware of the risk of co-infection of influenza virus and SARS-CoV-2. It also recommends that measures be put in place to mitigate the risk of children missing their immunisation because of possible school closures, in order to maximise coverage and minimise influenza community transmission.

Strengthening immunisation services

Increasing the number of people immunised is challenging and this year is compounded by a possible resurgence of COVID-19 cases, increased demand for the vaccine and staff absences. Pupil absences may also mean that immunisation teams will need to expand catch-up clinics or signpost parents to primary care. Settings that deliver immunisations will also have to manage services so that social distancing can be maintained, or to offer the vaccine in a wider range of settings that are more convenient for some people, such as drive-in centres.

Protecting at-risk groups

Those most at risk from influenza are also most at risk from COVID-19. A key objective of immunising children is to reduce community transmission of influenza as well as providing individual protection. Therefore it is essential that the coverage of the influenza programme is as high as possible. This will be challenging in the context of staff absences (in both health and education settings), possible school closures and pupil absences from school.

Groups in which coverage has consistently been lower than 50% (pregnant women and adults in at-risk groups) typically receive the vaccine from maternity services and GP practices. It is not clear why the level of coverage is lower than for over 65s, but recommendations to improve uptake were published by NICE in 2018. GP practices receive financial incentives to maximise coverage in eligible patient populations.

Services providing influenza immunisation have been given advice on preparing for this winter’s influenza season (EnglandNorthern IrelandScotlandWales). Vaccine providers have been directed to complete vaccinating their eligible population by the end of November and by 15 December for the schools programme.

Protecting health and social care workers

Immunising health and care workers protects the individuals and reduces sickness absence in the NHS. This reduces strain on the NHS during periods of peak demand in winter. It also reduces the risk of influenza to the workers’ families and patients. Last winter, 74.3% of frontline healthcare workers eligible for the vaccine were immunised. There were differences in coverage between primary and secondary care settings and between staff groups. Median coverage in NHS Trusts last winter was 79.5% (ranging from 44.8–94.8%). The staff group with the lowest uptake of vaccine was GP support staff at 59.4%. Vaccine uptake by staff in GP practices was lower overall than hospital staff, ranging from 47.2–71.8%.

Supply of vaccine and antiviral drugs

It is likely that international demand for influenza vaccines will outstrip supply this year. This is because manufacturers planned their production before the COVID-19 pandemic began and their ability to respond to unexpected demand is limited. Some companies have indicated that they will increase production, but it is unclear whether the UK will able to source adequate supplies of vaccines for the expanded adult programme. Immunisation providers were advised to order adequate supplies from manufacturers as usual. The Government has secured additional adult vaccine supplies to deliver the expanded programme and in anticipation of increased demand.

Antiviral drugs recommended for influenza are oseltamivir and zanamivir. Oseltamivir is one of the drugs subject to an export ban, to protect UK supplies.

Timeline of immunisation policy in the UK

9 April: Northern Ireland launches plans

The Chief Medical Officer of Northern Ireland issues a circular to health leaders, commissioners, hospitals and general practices on planning for the 2020–2021 season.

Evidence available on 9 April

September 2019: The Joint Committee on Vaccination and Immunisation publishes advice on which influenza vaccines should be used in which groups for winter 2020–2021.

21 May: Wales stresses importance of vaccination

The Welsh Government publishes a circular for health services, outlining the importance of increasing take up of vaccine by several groups and the need for effective planning, including ordering adequate supplies.

Evidence available on 21 May

21 May: SAGE notes that the prevalence of other respiratory infections are a critical determinant for the requirements of a test, trace and isolate programme.

26 June: Scotland release guidance

The Chief Medical Officer of Scotland publishes guidance for services providing the childhood immunisation programme.

24 July: England announces plan

24 July England: the Health and Social Care Secretary announces an expansion of the annual influenza immunisation programme

Evidence available on 24 July

2 July: SAGE endorses the independent paper Preparing for a Challenging Winter by the Academy of Medical Sciences. The reasonable worst case scenario described in that report is not endorsed by SAGE. SAGE recommends that preparations for winter should begin urgently across Government. SAGE reiterates its previous advice on expanded influenza immunisation, noting that people who have recovered from COVID-19 may be more susceptible to winter viruses and should be considered for vaccination. It also recommends that diagnostic tests be developed that can detect SARS-CoV-2 and influenza virus.

14 July: The Scottish Government COVID-19 Advisory Group discusses winter preparedness and the benefits of expanding eligibility for the influenza vaccine. The discussion also perceptions of the vaccine and the importance of clear communication to support uptake.

16 July: SAGE considers a report from the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) on the interaction of other respiratory viruses with SARS-CoV-2 and the implications for a winter resurgence of COVID-19.

5 August: Government and PHE release additional guidance

The Department of Health and Social Care and Public Health England publish further guidance on delivering the influenza immunisation programme. Target coverage is a minimum of 75% across all eligible groups. Providers are reminded of the need to minimise health inequalities and increase coverage in deprived areas and in BAME communities.

7 August: Scotland releases additional guidance

The Chief Medical Officer of Scotland publishes guidance for services providing the adult immunisation programme.

Related posts

  • Drug Therapies for COVID-19

    Research studies involving thousands of people have allowed scientists to test which drugs are effective at treating COVID-19. Several drug therapies are now available to treat people who are in hospital with COVID-19, or to prevent infections in vulnerable people becoming more serious. This briefing explains which drugs are available, the groups of people in which they are used and how they work. It also outlines the importance of monitoring the emergence of new variants and drug resistance.