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Under the influenza: impact of seasonal flu on children

JBN - 1343801/DOP - December 2011

Influenza remains an important cause of morbidity and mortality. In the UK, 3,000–4,000 deaths are attributed to influenza, the 'flu', each year, and this figure can increase tenfold during epidemics. High-risk groups for influenza include: Infants, children and adults with existing health complications; the over-65s; pregnant women; and frontline health and social care workers.(1-4)

Influenza viruses that affect humans are divided into two types: A and B, plus subtypes of A. Influenza A usually causes more severe illness than influenza B, and can result in pneumonia, hospitalisation or death, the elderly and chronically ill being particularly susceptible.

The viruses are antigenically unstable and mutate constantly.(2) Each year one or two subtypes of influenza A may be in circulation and one type of influenza B. Hence vaccines are determined yearly, prominent strains are detected and this information is used to predict future strains for inclusion into future vaccines.

Symptoms
Influenza is a highly contagious, acute viral infection that affects the nose, throat and lungs.(1) It cannot be distinguished from other acute respiratory illnesses on clinical grounds alone; laboratory tests are necessary.(2) Studies aimed at attempting to improve the predictive value of symptomatology have served only to raise the diagnostic success rate to one in three.

Influenza has a sudden onset, with symptoms including headache, chills and cough, usually followed by fever, appetite loss, muscle ache and tiredness.(5) Alternatively, cold symptoms are confined to the upper respiratory tract and are associated with runny nose, sneezing, throat irritation and watery eyes.

Gastrointestinal symptoms such as nausea, vomiting or diarrhoea can sometimes accompany influenza, particularly in children; however, the term 'stomach flu' often incorrectly describes gastrointestinal illness due to other causes. The period of infectiousness from the onset of symptoms is usually 3–5 days in adults and up to seven days in young children.

Impact on children
Influenza infections affect up to 3% of children aged 0-14 years in England in an average season, with young children (under five years of age) at greatest risk.(3,6) Indeed, rates of hospitalisation attributable to influenza in infants are similar to those in older adults.(7-11) Children are more likely than adults to experience influenza-related complications, such as middle-ear infections or pneumonia, requiring a higher rate of hospitalisations.(12-14)

Moreover, children and adolescents are the main transmitters of the influenza virus during local outbreaks, shedding greater quantities of the virus for longer periods of time and therefore passing the disease onto other children, family members and the wider community.(15-17)

The NHS burden of influenza in children is significant, with frequent primary care consultations in school age children.(10) Vaccinating children against influenza may interrupt virus transmission and protect those not immunised.(3) Yet vaccination of healthy children is not widespread in Europe despite potential benefits of vaccination – including the UK.(3,15-16) But the number of countries adopting universal vaccination in response to the burden in this age group is increasing.(3)

The direct benefits of vaccinating healthly children includes a reduction of the burden of disease in children.(3) It can protect against viral infection and common bacterial complications.(3) And it can ease the demands placed on resources by high numbers of medical visits, school and work absence, need for child care.(3)

But there are also some signficant indirect benefits of vaccination programmes, including a reduction in transmission of the influenza virus by protecting unvaccinated children and adults against infection.(3)

Fluenz nasal spray suspension influenza vaccine (live attenuated, nasal) is a new vaccine administered by spraying into the nose where it induces protective immunity. In several clinical studies it has demonstrated superior efficacy in children 24 months to less than 18 years of age compared to traditional inactivated influenza vaccines that are injected. The most common adverse events for LAIV (live attenuated influenza vaccine) are nasal congestion/rhinorrea, decreased appetite, headache, malaise and fever. The live influenza virus strains used in LAIV are cold-adapted, temperature sensitive and attenuated.

Each dose of Fluenz (SMPC) – which was licensed by the EMA in January 2011 – is formulated to contain three live attenuated influenza virus strains, which are weakened so as to not cause illness. The vaccine strains are selected annually by the World Health Organization (WHO) based on anticipated circulating influenza strains for the upcoming season. For more information please visit the website: www.astrazeneca.co.uk

References
1. Department of Health. Green Book. Pandemic influenza. London: DH; 2010. Available from: http://www.dh.gov.uk/health/category/policy-areas/public-health/immunisa...
2. PHLS. Public Health Laboratory Service; 2001.
3. Usonis V et al. Central European Vaccination Advisory Group (CEVAG) guidance statement on recommendations for influenza vaccination in children. BMC Infectious Diseases 2010;10:168.
4. Davies C et al. The influenza immunisation programme 2010/11. London: DH; 2010.
5. Population and Public Health Branch. Canada: PPHB; 2000.
6. Paget J et al. Assessing the burden of paediatric influenza in Europe: the European Paediatric Influenza Analysis (EPIA) project. Eur J Paediatr 2010;169(8):997-1008.
7. Jansen et al. Influenza- and respiratory syncytial virus associated mortality and hospitalizations. Eur Respir J 2007;30:1158–66.
8. Lenglet et al. Impact of flu on hospital admissions during 4 flu seasons in Spain, 2000–2004. BMC Public Health 2007;7:197.
9. Gasparini et al. Influenza and respiratory syncytial virus in infants and children: relationship with attendance at a paediatric emergency unit and characteristics of the circulating strains. Eur J Clin Microbiol Infect Dis 2007;26:619–28.
10. Pitman et al. Assessing the burden of influenza and other respiratory infections in England and Wales. Journal of Infection 2007;54:530-8.
11. Weigl et al. Epidemiol. The incidence of influenza-associated hospitalizations in children in Germany. Infect 2002;129:525–33.
12. Clements DA et al. Influenza A vaccine decreases the incidence of otitis media in 6- to 30-month-old children in day care. Arch Pediatr Adolesc Med 1995;149:1113-17.
13. Heikkinen T et al. Influenza vaccination in the prevention of acute otitis media in children. Am J Dis Child 1991;145:445-8.
14. Belshe RB et al. The efficacy of live attenuated, cold-adapted, trivalent, intranasal influenza virus vaccine in children. N Engl J Med 1998;338:1405-12.
15. Neuzil KM et al. Illness among schoolchildren during influenza season: effect on school absenteeism, parental absenteeism from work, and secondary illness in families. Arch Pediatr Adolesc Med 2002;156:986-91.
16. Heikkinen T et al. A consensus report of the Summits of Independent European Vaccination Experts. Eur J Pediatr 2006;165(4): 223-8.
17. Hall CB et al. Viral shedding patterns of children with influenza B infection. J Infect Dis 1979;140(4):610-13.

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