Influenza infection

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Your Organizational Guidance

ebpracticenet urges you to prioritize the following organizational guidance:

Prévention de l’InfluenzaPublished by: Groupe de travail Développement de recommandations de première ligneLast published: 2018Preventie van influenzaPublished by: Werkgroep Ontwikkeling Richtlijnen Eerste Lijn (Worel)Last published: 2018

In the 2020/21 season, influenza activity levels were extremely low as a result of measures to prevent coronavirus disease 2019 (COVID-19) (such as handwashing, mask-wearing, physical distancing, and restricted travel) and continued to be low in the 2021/22 season. In the 2022/23 season, there was a resurgence of influenza activity as social contact returned to normal.[8][9][10] Influenza vaccination is encouraged as a measure to relieve winter pressure on health care providers. Influenza vaccine and COVID-19 vaccine may be administered at the same visit.[30][38]

Primary prevention for influenza is provided by the influenza vaccine.[39][40][41][42][43][44][45][46][47] Influenza vaccines are prepared using virus strains in line with WHO recommendations. Quadrivalent influenza vaccines contain two subtypes of influenza A and two subtypes of influenza B; trivalent vaccines contain two subtypes of influenza A and one B virus. All vaccines apart from the live attenuated influenza vaccine (LAIV) are inactivated. In addition to primary prevention of seasonal influenza infection, receipt of influenza vaccination may also attenuate the course of disease in those with breakthrough infection.[48][49]

International guidelines vary in their recommendations of who should receive vaccination. In the UK for 2024-2025, influenza vaccination is recommended for all children aged 2 and 3 years on 31 August 2024, all primary school-aged children (from reception to Year 6), secondary school-aged children focusing on Years 7 to 11, all people aged 65 years or over, people aged from 6 months to less than 65 years who are in clinical risk groups (e.g., chronic respiratory, heart, kidney, liver, or neurological disease, diabetes, immunosuppression, learning disability, obesity), pregnant women, close contacts of people vulnerable to infection (e.g., those who are immunocompromised, those at risk from severe COVID-19 illness), carers, health and social care workers, and those who live in residential care homes.[50]

The US Centers for Disease Control and Prevention (CDC) currently recommends influenza vaccine for all people aged ≥6 months who do not have contraindications to vaccination.[30] CDC: influenza (flu) Opens in new window For 2023-2024, the CDC Advisory Committee on Immunization Practices (ACIP) recommend that any licensed, quadrivalent, age-appropriate influenza vaccine may be used, including LAIV where it is appropriate.[30] Adults aged ≥65 years should preferentially receive one of the higher dose or adjuvanted influenza vaccines (quadrivalent high-dose inactivated influenza vaccine, quadrivalent recombinant influenza vaccine, or quadrivalent adjuvanted inactivated influenza vaccine). If none of these preferred vaccines is available, then any other age-appropriate influenza vaccine can be used.[30] The American Academy of Pediatrics (AAP) also recommends any licensed, recommended, age-appropriate vaccine may be used for children, without preference for one product or formulation over another (unless contraindicated).[17] Children aged 6 months to 8 years require two doses of influenza vaccine (administered ≥4 weeks apart) during their first season of vaccination to optimise response.[30] The ACIP recommends that children aged 6 months to 8 years who have previously received ≥2 doses of trivalent or quadrivalent influenza vaccine ≥4 weeks apart before July 1, 2023 require only one dose for 2023-2024.[30] Beginning at age 9 years, only one annual dose is recommended.[30]

Pregnant women may receive any licensed, recommended, age-appropriate inactivated vaccine; LAIV should not be used during pregnancy.[30][33] Influenza vaccination during pregnancy is not associated with an increased risk of adverse health outcomes in infants in early childhood.[51][52][53][54][55] It may help prevent influenza hospitalisations among pregnant women.[56] Additionally, influenza vaccination during pregnancy results in antibody development that can protect infants in the first few months of life.[57]

Immunocompromised people are at higher risk of complications from influenza infection and should be vaccinated with any licensed, recommended, age-appropriate inactivated vaccine. Inactivated vaccines should be used with caution in severely immunocompromised patients (e.g., patients receiving chemotherapy, radiotherapy, or other immunosuppressive therapy, including high-dose corticosteroids), as there may be a reduced response to vaccination. However, adjuvanted vaccine has been shown to be safe and immunogenic in the transplant population.[28] Intranasal live-attenuated vaccine is contraindicated in immunosuppressed or immunocompromised patients. Inactivated influenza virus vaccine is also preferred over live virus vaccine for household members, healthcare workers, and others coming into close contact with severely immunosuppressed people requiring care in a protected environment.[29]

People who did not receive the current seasonal influenza vaccine and who are travelling to areas where influenza activity is ongoing, should consider influenza vaccination ≥2 weeks before departure.[58]

In the US, the AAP and the ACIP recommend that all people aged ≥6 months with egg allergy can receive any influenza vaccine (that is appropriate for their age and health status) without any additional precautions beyond those recommended for any vaccine.[17][30] UK guidelines advise that children who have required admission to intensive care for a previous severe anaphylaxis to egg are given LAIV in the hospital setting.[59]

Regardless of allergy history, all vaccines should be administered in settings in which personnel and equipment for rapid recognition and treatment of anaphylaxis are available.

The ACIP recommends that the LAIV should not be given to the following people:[30][60][61]

Children younger than 2 years and adults 50 years and older
Children age 2 to 17 years who are receiving aspirin- or salicylate-containing medications
Children age 2 to 4 years old who have asthma or a history of wheezing in the past 12 months
People who are immunocompromised (any cause)
People with anatomic or functional asplenia
Close contacts or caregivers of severely immunosuppressed persons who require a protected environment
Pregnant women
People with cranial cerebrospinal fluid/oropharyngeal communications
People with cochlear implants
People who have taken oseltamivir or zanamivir within the previous 48 hours, peramivir in the previous 5 days, or baloxavir in the previous 17 days.

Vaccine effectiveness may vary according to the age of the recipient, the level of pre-existing immunity, and correctly predicting the specific circulating strains of virus.[41][42][43][44][62][63][64][65][66][67][68][69] [ ] [ ] [ ] [Evidence B]

Vaccine efficacy in older people:

Most influenza-associated deaths occur in the older population (aged ≥65 years).[70][71][72] A systematic review found that benefits of vaccination were more evident on health-related outcomes of residents in long-term care facilities than in healthy older individuals in the community.[73] A pooled cohort study published after the meta-analyses demonstrated a significant reduction in mortality in vaccinated older individuals (1.0% versus 1.6% in unvaccinated individuals).[71] The mortality benefit in older patients is increased with annual vaccination.[74] High-dose vaccination and boosting low titres midseason may be of benefit in older people.[75][76][77][78][79]
Any licensed, age-appropriate vaccine may be used; the ACIP recommends those aged ≥65 years preferentially receive one of the higher dose or adjuvanted influenza vaccines (quadrivalent high-dose inactivated influenza vaccine, quadrivalent recombinant influenza vaccine, or quadrivalent adjuvanted inactivated influenza vaccine).[30] UK guidelines recommend that those aged over 65 years should receive adjuvanted quadrivalent inactivated influenza vaccine or quadrivalent recombinant influenza vaccine; quadrivalent influenza cell-culture vaccine can also be considered for use in this group if other options are not available.[50]

Guillain-Barre syndrome (GBS) risk:

GBS is an acute autoimmune disorder of peripheral nerves that develops in susceptible individuals after infection and, in rare cases, after immunisation. In the US, an increased risk of GBS was associated with the 1976 swine influenza vaccine (swine-origin influenza A H1N1 subtype A/NJ/76).[80] The number of reports of influenza-vaccine-associated GBS to the national Vaccine Adverse Event Reporting System increased from 37 in 1992-1993 to 74 in 1993-1994. Studies of these cases showed that for the two seasons combined, the adjusted relative risk of 1.7 suggests slightly more than 1 additional case of GBS per million people vaccinated against influenza.[81] This risk seems to be substantially less than the overall health risk posed by naturally occurring influenza.
A history of GBS within 6 weeks following receipt of influenza vaccine is a precaution for the use of influenza vaccine because of the risk of recurrent GBS. Risks and benefits of vaccination need to be considered in these instances.[30]

Secondary prevention

Chemoprophylaxis can be considered for high-risk people who are unable to receive the vaccine due to contraindications, unavailability, or ineffectiveness of the vaccine.[2][109][110] Residents of any institutions, such as nursing homes, that are experiencing an influenza outbreak should receive chemoprophylaxis for influenza regardless of immunisation status.

Both oseltamivir and zanamivir have been shown to be effective as prophylaxis against infection when given early after exposure to an infected individual. [ ] One meta-analysis has shown that oseltamivir used prophylactically may reduce the spread of symptomatic influenza within households.[121]

Baloxavir marboxil is now approved in the US for post-exposure prophylaxis of influenza in patients aged 5 years and older following contact with an individual who has influenza. In phase 3 trials, single-dose baloxavir was effective in preventing influenza in household contacts (both adults and children) of patients with influenza.[133][134] Use of baloxavir is not recommended in people who are severely immunosuppressed.[110]

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