MINI-SYMPOSIUM: RESPIRATORY VIRUSES – PART I
Influenza virus infection in infancy and early childhood

https://doi.org/10.1016/S1526-0542(03)00027-7Get rights and content

Abstract

Infants and young children have the highest influenza infection and hospitalisation rates in paediatrics. The immaturity of the infant’s immune system and the absence of prior immunity and exposure to the virus are potential contributors. Although most children that suffer from influenza infection are otherwise healthy, an underlying chronic medical condition further increases the risk for complications. Annual immunisation with influenza vaccine is recommended for any child 6 months of age and older in whom prevention of disease is desirable, particularly for those with underlying medical conditions. Offering influenza vaccine to pregnant women who will deliver during the influenza season can potentially reduce the frequency and severity of influenza disease in infants less than 6 months of age. Family members, including other children and all other close contacts, should also receive influenza vaccine to reduce transmission to children at risk and infants in the first 6 months of life.

Section snippets

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

  • Infants and children less than 2 years of age have the highest risk of hospitalisation for severe influenza and influenza-associated complications in paediatrics.

  • The clinical presentation of influenza disease may be atypical in infants.

  • 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.

RESEARCH DIRECTIONS

  • Improved methods for rapid and early diagnosis of influenza infection.

  • The protective effect of maternal immunisation with influenza vaccine on the frequency and severity of infant disease.

  • 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.

  • The herd immunity effect of influenza vaccine when used as a universal immunisation strategy.

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