MINI-SYMPOSIUM: RESPIRATORY VIRUSES – PART IInfluenza virus infection in infancy and early childhood
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INTRODUCTION
The impact of influenza epidemics varies from year to year depending on the virulence of the circulating virus strain, the presence or lack of prior immunity to the epidemic virus in the population and the intensity of exposure to the virus. The direct impact of influenza in young children can be difficult to assess because clinical manifestations of influenza in infants are often atypical and because they are susceptible to infection with many other respiratory viruses with activity coinciding
CLINICAL PRESENTATION OF INFLUENZA
The clinical presentation of influenza in children varies in different age groups, but in general, influenza is more commonly associated with a febrile illness than other respiratory viruses.1 After an incubation period of 1–4 days, uncomplicated influenza in older children and adults is characterised by a sudden onset of fever that can be accompanied by chills and sweats, myalgia, malaise, headache, non-productive cough, rhinitis and sore throat. In children younger than 5 years, fever, cough
EPIDEMIOLOGY AND IMPACT OF INFLUENZA IN YOUNG CHILDREN
Children play a significant role in the introduction and spread of influenza virus into households and in the community.16 Cases among school-age children usually peak in the early stage of an epidemic and are followed by cases in infants and adults.17 The presence of school-age children in the household is the most important determinant related to the occurrence of influenza infection. There is also evidence that seroconversion to influenza virus in children continues to occur between
CHILDREN AT HIGH RISK FOR INFLUENZA MORBIDITY AND MORTALITY
Children with underlying medical conditions have rates of hospitalisation for influenza-related illnesses two to six times higher than in otherwise healthy children. In studies of epidemics from the 1960s to the early 1990s, the highest rates of hospitalisation in high-risk children were observed in those under 5 years of age15., 23., 29. and particularly in children under 1 year of age, who have hospitalisation rates two to four times higher than those of healthy children of similar age in the
MATERNAL ANTIBODIES AND PROTECTION FROM INFLUENZA
Most influenza infections in infants under 1 year of age occur in the second 6 months of life.36 Considering the high infection rates observed in school-age children, infants are at greater risk of infection if they are exposed to the virus by contact with older siblings or other children in out-of-home care environments.36., 37. Maternally derived antibodies are likely to provide protection against influenza in the first 6 months after birth. The degree and duration of protection is directly
DIAGNOSIS OF INFLUENZA IN INFANTS
The accuracy of clinical diagnosis of influenza may be up to 85% at best for experienced clinicians, although it is lower with decreasing patient age. Laboratory confirmation can be achieved by virus isolation, or detection of viral proteins, viral RNA or antibodies to influenza. Culture-confirmed cases of influenza only account for approximately one-third of all cases because of the limitations of viral-isolation techniques, including the timing of specimen collection in relation to onset of
TREATMENT OF INFLUENZA IN INFANTS
There are no anti-virals licensed for the treatment of influenza in infants younger than 1 year of age. Four anti-virals are licensed in the USA for the treatment of influenza in older children, and three anti-virals are approved for prophylaxis (Table 1). In order to be effective, treatment must be started within 48 h of the onset of symptoms. The most important intervention to protect infants against influenza is prevention through immunisation.
PREVENTION OF INFLUENZA
Annual immunisation with influenza vaccine is currently recommended in the USA for children 6 months of age and older with any underlying condition that increases their risk for severe illness and mortality (Table 2).26 In 2002, the Advisory Committee on Immunization Practices (ACIP) released a statement encouraging annual influenza immunisation in children 6–23 months of age who are otherwise healthy, due to their higher risk of hospitalisation and complications from influenza.57., 58.
There
PRACTICE POINTS
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Infants and children less than 2 years of age have the highest risk of hospitalisation for severe influenza and influenza-associated complications in paediatrics.
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The clinical presentation of influenza disease may be atypical in infants.
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In the USA, vaccination with trivalent inactivated influenza vaccine is highly encouraged for all children 6–23 months of age, and recommended for children 6 months of age and older with underlying cardiopulmonary diseases or other chronic high-risk conditions.
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RESEARCH DIRECTIONS
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Improved methods for rapid and early diagnosis of influenza infection.
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The protective effect of maternal immunisation with influenza vaccine on the frequency and severity of infant disease.
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The safety of the intranasal trivalent live attenuated influenza vaccine in children <5 years of age, adults >50 years of age, and persons with underlying chronic diseases.
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The herd immunity effect of influenza vaccine when used as a universal immunisation strategy.
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The effectiveness of influenza vaccination in pregnancy in relation to child health outcomes: Systematic review and meta-analysis
2020, VaccineCitation Excerpt :Infants are highly susceptible to influenza illness, partly due to the anatomical and physical features of infancy, and due to absence of prior exposure to the virus and development of immunity. Unfortunately, no influenza vaccines are licensed for infants aged ≤6 months old [9,10]. For the infant, influenza infection is associated with increased rates of hospitalisation and higher death rates [1,11,12].
Underdetection of laboratory-confirmed influenza-associated hospital admissions among infants: a multicentre, prospective study
2019, The Lancet Child and Adolescent HealthChild hospital admissions associated with influenza virus infection in 6 Spanish cities (2014-2016)
2019, Anales de PediatriaClinical effectiveness of four neuraminidase inhibitors (oseltamivir, zanamivir, laninamivir, and peramivir) for children with influenza A and B in the 2014–2015 to 2016–2017 influenza seasons in Japan
2018, Journal of Infection and ChemotherapyCitation Excerpt :It has been reported that duration of fever in patients with influenza tended to be shorter in old children than in young children when they were treated with oseltamivir, zanamivir or laninamivir [25–28]. These results might be explained partially by immaturity of the immune system against influenza viruses in younger children [29]. The duration of fever after administration of the first dose of the NAI was shorter in patients with influenza A infection than in patients with influenza B infection at all ages (Tables 2 and 3).