Vacunación contra la influenza

Not to be confused with the Haemophilius influenzae vaccine.

Influenza (flu) is a major cause of morbidity and mortality each year in the UK. Admissions to hospital in the UK tend to peak between December and February with the highest numbers of admissions with proven influenza (both to hospital and to intensive therapy units) being in those under the age of 4 and those over the age of 65.¹

Vaccination has been available since the late 1960s. It is offered annually to children from age 2 up to those in year 11 at school, pregnant women, patients aged over 65 years, and to all people at higher risk of serious influenza infection between the ages of 6 months and 65 years. It is also offered to people in long-stay care facilities and, from 1 October 2026, to those who are homeless. Healthcare staff should also be offered the influenza vaccine.

All but one of the influenza vaccines available in the UK are inactivated and do not contain live viruses. Inactivated vaccines are usually administered intramuscularly. Inactivated influenza vaccines contain two subtypes of influenza A and two subtypes of influenza B virus. Fluenz® is a trivalent attenuated live vaccine administered by nasal spray.

Unfortunately there have been some changes in 2026 to the NHS guidance which means that health care assistants are unable to consent for flu vaccines under a PGD. This will create increasing barriers to access to influenza immunisations.

Influenza vaccines²

Influenza strains for the vaccines are selected each year based on international surveillance of circulating influenza viruses. The use of quadrivalent influenza vaccines containing a B strain from each lineage was expected to improve the match of the vaccine and therefore offer wider protection against circulating influenza B flu viruses.

Because influenza B has previously been relatively more common in children, the vaccines for the childhood programme in recent years have been quadrivalent preparations, containing two influenza A and two influenza B lineages. However, B/Yamagata strains have not been detected in the UK since 2020,³ and these appear not to be circulating globally either. WHO has recommended the removal of B/Yamagata strains as soon as possible from influenza vaccines;⁴ the live attenuated vaccine for influenza has now become a trivalent vaccine again.⁵

The LAIV is thought to provide broader protection than inactivated vaccines, and therefore has potential to offer better protection against strains that have undergone antigenic drift compared to the original virus strains in the vaccine. LAIV has been shown to provide a higher level of protection for children than inactivated influenza vaccines.

Recommendations for use (2026-27)⁶

The following groups of people in England are eligible for a flu vaccine from 1 September 2026 as part of the NHS flu immunisation programme:

• All children who were 2 or 3 years old on 31 August 2026.

• All children in school, from reception to year 11.

• All pregnant women, at any stage of pregnancy.

• Anyone aged 6 months to 18 years in a clinical risk group (see below).

The following groups will be eligible for vaccination from 1 October 2026:

• Todas las personas de 65 años o más.

• Everyone aged 18 years to under 65 years who has a medical condition listed below.

• Todos los que viven en una residencia o en un hogar de ancianos.

• Personas que reciben una asignación por cuidado, o aquellas que son el cuidador principal de una persona mayor o discapacitada.

• Close contacts of immunocompromised people.

• Todo el personal de atención social en primera línea sin un esquema ocupacional dirigido por el empleador.

Influenza vaccination should ideally be completed by the end of November but can also take place up until the following 31 March.

Adults with a body mass index of 40 kg/m² or above are also eligible.

Chapter 19 of the 'Green Book' provides the relevant details for Scotland, Wales, and Northern Ireland.²

GPs should take into account the risk of influenza infection exacerbating any underlying disease that a patient may have, as well as the risk of serious illness from influenza itself. GPs should consider on an individual basis the clinical needs of their patients, including individuals with:

• Multiple sclerosis and related conditions.

• Hereditary and degenerative diseases of the central nervous system.

Individuals working closely with poultry are no longer thought to be high-risk.

Employers - eg, healthcare trusts and nursing and care homes - should offer influenza vaccination to staff directly involved in patient care as an adjunct to good infection control procedures:

• Clinicians, midwives and nurses, paramedics and ambulance drivers.

• Occupational therapists, physiotherapists, and radiographers.

• Primary care providers such as GPs, practice nurses, and district nurses.

• Staff who look after older people in nursing and care homes.

Method of administration²

In all settings providing vaccination, facilities should be available and staff trained to recognise and treat anaphylaxis.

• Vaccines are normally given intramuscularly into the upper arm or anterolateral thigh.

• The live attenuated influenza vaccine (LAIV), Fluenz®, is a nasal spray used for children aged 2-18 years.

• If patients have a bleeding disorder (eg, haemophilia), deep subcutaneous injection is appropriate.

• Influenza vaccine can be given with other vaccines, preferably in different limbs. If both vaccines have to be given in the same limb, the sites should be at least 2.5 cm apart.

• The batch numbers and sites of the vaccines should be recorded in the patient's notes.

• If the vaccine is given for employment purposes, the employer should also keep a record.

Vaccine uptake⁷

In the 2025-2026 influenza vaccine season

• 65 years and over: 74.5%.

• 6 months to under 65 years at-risk: 40.6%.

• Pregnant women: 38.4%.

• All 2- and 3-year-olds: 44.2%.

Eficacia²

The effectiveness of influenza vaccine depends upon the composition of the vaccine, the circulating strains, the type of vaccine and the age of the individual being vaccinated.

• The LAIV is thought to provide broader protection than inactivated vaccines, and therefore has potential to offer better protection against strains that have undergone antigenic drift compared to the original virus strains in the vaccine.

• LAIV has been shown to provide a higher level of protection for children than trivalent inactivated influenza vaccine. A meta-analysis suggested an efficacy against confirmed disease of 83%.

• Immune responses to vaccination decline substantially with age.

Storage, presentation, and disposal²

• Influenza vaccines should be stored in their original packaging at +2°C to +8°C and protected from light.

• LAIV may be left out of the refrigerator/removed from the cold chain for a maximum period of 12 hours at a temperature not above 25°C. If the vaccine has not been used after this 12-hour period, it should be disposed of.

• Extremes of temperature can reduce potency. Freezing can cause hairline cracks in the container.

• All vaccines are supplied in the inactive form in pre-filled syringes (or a nasal applicator) which should be shaken before use.

• Dispose of the vaccination equipment in a sealable, puncture-proof sharps box (UN-approved BN7390).

Dosificación y calendario²

There is specific guidance for specific situations. The Green Book should be used for advice on dosing and schedules. For the majority of adults, one intramuscular dose of the inactivated vaccine should be used. For the majority of children, a single dose of the live nasal vaccine is used but there may be specific scenarios where the inactivated vaccine should be used instead - for example, household contacts of immunocompromised patients.

Contra-indications to all influenza vaccinations²

There are few contra-indications. When in doubt, seek the guidance of a local communicable disease consultant, paediatrician, or immunisation co-ordinator. Vaccine should not be given to patients with:

• A confirmed anaphylactic reaction to a previous dose of the vaccine.

• Una reacción anafiláctica confirmada a cualquier componente de la vacuna.

LAIV should not be given to children or adolescents who are clinically severely immunocompromised due to conditions or immunosuppressive therapy.

A careful history should rule out previous non-life-threatening reactions (eg, rash, or reactions which were not truly anaphylactic). Seek the advice of a specialist when in doubt.

In addition, live attenuated vaccines are contra-indicated for those who:

• Are clinically severely immunodeficient secondary to a condition or immunosuppressive therapy.

• Are receiving salicylate therapy.

• Have a household member who is severely immunocompromised.

Children who have acute wheezing at the time of vaccination or in the preceding 72 hours, should not be given the live attenuated vaccine and should be offered inactivated vaccine to avoid delays in vaccination.

Some parents have concerns about porcine gelatine in the LAIV. They should be informed that the vaccines themselves contain no gelatine and that most Muslim and Jewish leaders feel that the LAIV does not contra-indicate religious laws. ⁸If they continue to refuse the LAIV they can have the injectable vaccine but this is less effective for children.

Historically children with egg allergy have been advised not to have the LAIV but this is no longer the case.

Precauciones²

• Intercurrent illness - vaccination may be postponed in the event of an acute illness, but minor illness without pyrexia or systemic upset should not be a reason for delay.

• Premature infants - at-risk premature infants should have vaccination at the appropriate chronological age.

• HIV infection - immunosuppressed patients should be given the vaccine, irrespective of CD4 count. A full antibody response may not be produced. See above also for Fluenz®.

Side-effects of influenza vaccine²

• Angioedema, urticaria, bronchospasm, and anafilaxia can occur. This is an immediate allergic reaction, usually due to hypersensitivity to residual egg protein.

• Neuralgia, paraesthesiae, convulsions, and transient thrombocytopenia have been reported rarely.

• Síndrome de Guillain-Barré has very rarely been reported (1-2 cases per million vaccinated people) and only a single case was proven in 1976. There is a very strong link between GBS and influenza infection (17.2 cases per million hospitalised patients) so any theoretical risks associated with vaccination are significantly lower than those associated with disease.⁹

• Encephalomyelitis, neuritis (mainly optic), and vasculitis have also (very rarely) been reported but a definite causal relationship with influenza vaccine has not been established.

• All suspected reactions in children and severe suspected reactions in adults should be reported using the Yellow Card Scheme to the Commission on Human Medicines.¹⁰