Influenza is an acute viral disease of the respiratory tract caused by the influenza virus.
- Transmitted by airborne droplets among crowds and in enclosed spaces.
- May also occur through direct contact with respiratory secretions and infected individuals.
- Hand contamination is a source of transmission.
Three different virus types of influenza are recognised: A, B and C.
- Types A and B occur more frequently.
- Type A has further subtypes e.g. A(H1N1).
Epidemics of influenza occur almost every year and are caused primarily by type A virus.
- Northern hemisphere influenza season is November-April.
- Southern hemisphere influenza season is April-September.
In tropical areas there is no clear seasonal pattern but peaks during rainy season.
- Incubation period is short, 1-3 days.
- Convalescence/recovery usually 2-7 days.
Risk of Severe Illness
- Viral pneumonitis.
- Bacterial pneumonia.
- Middle ear infection.
- Exacerbation of underlying chronic conditions.
Severe illness and death during annual influenza epidemics occur primarily among those in the high risk group categories e.g.:
- Over 65 years.
- Chronic medical conditions.
Signs and Symptoms
- Muscle pain.
- Head cold.
- Sore throat.
Treatment of influenza is mainly supportive and the relief of symptoms.
There are antiviral drugs available that can be used to prevent or treat influenza but only under special circumstances and medical advice.
Travellers to countries during their influenza season are at similar risk of infection as local residents.
Crowded conditions encourage spread of infection and travellers can be exposed, for example in those attending pilgrimages, in aircraft, waiting rooms, buses, bars, hotels and on cruises.
When to Consider Vaccination
Vaccination should be considered under the following circumstances and is dependent on the individual risk assessment:
- Travellers in the influenza risk groups in the UK should ensure that they have received their seasonal influenza vaccine before travel.
- Travellers to the southern hemisphere (SH) during the destination influenza season may not be able to obtain SH vaccine in the UK prior to travel. The traveller should therefore try to arrange for vaccination after arriving at their travel destination.
- Those more likely to be exposed to very crowded conditions e.g. attending large gatherings, festivals and major sporting events, particularly if during influenza season in the particular region or during outbreaks.
- The Saudi Ministry of Health recommends seasonal influenza vaccine for Hajj attendees before arrival, especially for those at increased risk e.g. the elderly, those with chronic chest or heart disease.
- Travellers not in high risk groups may wish to be vaccinated to reduce the risk of an important short trip being disrupted by influenza.