Flu season is around the corner…

Sr JM McAnerney, Dr S Walaza, Dr C Cohen Centre for Respiratory Diseases and Meningitis National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS)

As in other temperate Southern and Northern Hemisphere countries, South Africa experiences seasonal influenza epidemics every winter. Although the timing of the influenza season varies from year to year, influenza virus circulation occurs mainly during the winter months of May to August, but may start as early as April or as late as July. The average duration of the influenza season over the past 13 years has been 19 weeks.

Despite an effective influenza vaccine having been available for many years, influenza continues to cause significant morbidity and mortality worldwide. Annually influenza epidemics are estimated to cause between 3 and 5 million cases of severe illness leading to hospitalisation, and between 250 000 and 500 000 deaths worldwide.

In sub-Saharan Africa, and specifically in South Africa, the burden of influenza is substantial, with studies showing higher influenza-associated mortality rates compared to other regions.3 Annual estimates of between 7000 and 12000 seasonal influenza-associated deaths have been reported for South Africa.

Diagnosis and symptoms

It is difficult to distinguish illness due to influenza from that due to other respiratory viruses clinically. Influenza is usually an uncomplicated illness, which is characterised by sudden onset of constitutional and respiratory symptoms such as fever, myalgia, cough, sore throat, rhinitis and headache. Influenza typically resolves in 3-7 days in the majority of people, although, cough and malaise may persist for several weeks. In a proportion of patients, influenza may be associated with more severe complications, these complications include: Viral pneumonia, secondary bacterial or viral infections (including pneumonia, sinusitis and otitis media), and exacerbations of underlying illnesses (e.g. pulmonary and cardiac illness).

Certain groups of people are at higher risk for serious complications of influenza, these include:

  • Pregnant women (including the post-partum period)
  • HIV–infected individuals
  • Infants and young children (particularly <2 years of age)
  • Individuals with tuberculosis
  • Persons of any age with chronic diseases, including:
  • Pulmonary diseases (e.g. asthma, COPD)
  • Immunosuppression (e.g. persons on immunosup- pressive medication, malignancy)
  • Cardiac diseases (e.g. congestive cardiac failure)
  • Metabolic disorders (e.g. diabetes)
  • Renal disease
  • Hepatic disease
  • Certain neurologic and neurodevelopmental conditions, including: Disorders of the brain, spinal cord, peripheral nerve, and muscle such as cerebral palsy, epilepsy (seizure disorders), stroke, mental retardation, moderate to severe developmental delay, muscular dystrophy or spinal cord
  • Haemoglobinopathies
  • Persons ≤18 years receiving chronic aspirin therapy
  • Persons aged ≥65 years
  • Persons who are morbidly obese (i.e. BMI ≥40).

Prevention and treatment

Influenza vaccine remains the primary means for preventing seasonal influenza infection. The World Health Organization updates the candidate vaccine every year, based on data collected in the Global Influenza Surveillance Programme. The annual seasonal influenza vaccine contains strains corresponding antigenically, as close as possible, to the most recently circulating of the three seasonal influenza strains causing disease in human populations: Influenza A(H1N1), influenza A(H3N2) and influenza B. Updated recommendations for influenza vaccination in South Africa are published annually (http://www.nicd.ac.za). Several formulations of seasonal influenza vaccine are available and licensed for use in South Africa. Annual vaccines should contain 15μg of each haemagglutinin antigen in each 0.5ml dose. The vaccine formulation for the 2019 influenza season contains an A/Michigan/45/2015 (H1N1)pdm09-like virus, an A/Switzerland/8060/2017 (H3N2)-like virus, and a B/ Colorado/06/2017-like virus (B/Victoria/2/87 lineage).

A protective antibody response takes about 2 weeks to develop, hence vaccines should be administered sufficiently early to provide protection for the winter, although it is never too late to vaccinate. Vaccine effectiveness differs amongst age groups, and is dependent on the age and health of the recipient. Vaccine effectiveness is also dependent on the match between the virus strains in the vaccine and those actually circulating in the community.

The dose in adults is one 0.5 ml dose intramuscularly of the whole, split-product or subunit vaccine. Similarly in children aged 9-12 years one dose of the split-product or subunit vaccine may be used. Children 3-9 years, who have never been vaccinated, should receive 2 doses in total, the initial dose and a further dose one month later. Children 6 months-3 years of age should receive half the adult dose on two occasions separated by month. Influenza vaccine is not recommended for infants aged <6 months.

Adverse events following vaccination are rare, occurring in between 0.5 and 1 % of vaccinations.6 The most common side effects of the vaccine are local swelling, redness or tenderness at the site of the injection, and more rarely low-grade fever or myalgia. If these reactions occur they usually begin soon after vaccination and last no more than 1-2 days. The influenza vaccine is an inactivated virus, therefore, the vaccine does not cause influenza.

Contraindications to influenza vaccination

  • Persons with a history of severe hypersensitivity to eggs
  • Persons with acute febrile illnesses should preferably be immunised once symptoms have

In conjunction with vaccination, patients should receive advice regarding general preventative precautions such as hand washing, cough hygiene and avoiding contact with people. Patients with clinical influenza should be advised to stay at home during the cause of symptoms to protect colleagues, other children at school and the general population they may come into contact with.

Oseltamivir (Tamflu®) may decrease the duration and severity of influenza illness and should only be considered in high-risk patients, such as those listed in this article. Prophylaxis with oseltamivir (Tamflu®) may also be considered in high-risk patients who have been exposed to confirmed influenza. Patients who are not considered high risk may be treated symptomatically.

Conclusion

Influenza vaccination, although not 100% effective, remains the best available form of protection against influenza, which still causes significant morbidity and mortality worldwide. Influenza vaccine should be given before the start of the influenza season, especially to individuals who fall in the groups recommended for influenza vaccination. The start of the influenza season is posted on the National Institute for Communicable Disease (NICD) webpage. In addition, graphs detailing the influenza season are posted weekly during the season. (http://www.nicd.ac.za).

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