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| INFLUENZA |
Disease
Influenza is an acute respiratory illness cause by influenza viruses. The illness affects the upper and/or lower respiratory tract and is often accompanied by systemic signs and symptoms such as fever, headache, myelgia and weakness. Outbreaks of illness of variable extent and severity occur nearly every winter. Such outbreaks result in significant morbidity in general population and increased mortality rates among certain high risk patients mainly due to pulmonary complications.
Occurrence
Influenza outbreaks are recorded virtually every year although there extent and severity vary widely. Localized outbreaks take place at variable intervals usually every 1 to 3 years. Global pandemics have occurred at variable intervals but less frequently than inter pandemics outbreaks.
Risk for travellers
In the tropics, influenza can occur throughout the year. In the southern hemisphere, peak activity occurs between April and September and in the northern hemi-sphere between November and March. Influenza transmission may be enhanced in crowded conditions associated with air travel, cruise ships and tour groups. Elderly people and individuals with respiratory and cardiac disease, diabetes mellitus or any immunosuppressive condition are particularly at risk of more severe disease. The impact of an attack of influenza during travel can range from highly inconvenient to life-threatening.
Vaccine
Inactivated and live attenuated vaccines against influenza A & B are available and their use is one of the major steps in the prevention of influenza.
Influenza viruses constantly evolve, with rapid changes in their antigenic characteristics. To be effective, influenza vaccines need to stimulate immunity to the principal strains of virus circulating at the time. In a very limited number of countries, a live vaccine is being used. The internationally available vaccines contain three inactivated viral strains, with the composition being modified every 6 months to ensure protection against the strains prevailing in each influenza season. Since the antigenic changes in circulating influenza viruses occur very rapidly, there may be significant differences between prevailing strains during the influenza seasons of the northern and southern hemispheres, which occur at different times of the year. Vaccine composition is therefore adjusted for the hemisphere in which the vaccine will be used. Thus, a vaccine obtainable in one hemisphere may offer only partial protection against influenza infection in the other.
Since influenza vaccines will not control epidemics, they are recommended only for persons at high risk. Annual immunization is strongly recommended for individuals aged over 6 months with the following conditions:
- Chronic respiratory disease (includes asthma treated with continuous or repeated use of inhaled or systemic corticosteroids or asthma with previous exacerbations requiring hospital admission);
- Chronic heart disease;
- Chronic liver disease;
- Chronic renal disease;
- Chronic neurological disease
- Diabetes mellitus
- Immunosuppression because of disease (including asplenia or splenic dysfunction) or treatment (including prolonged corticosteroid treatment) ;
- HIV infection (regardless of immune status).
Influenza immunization is also recommended for all persons aged over 65 years, for residents of nursing or residential homes for the elderly and other long-stay facilities, and for carers of persons whose welfare may be at risk if the carer falls ill. Influenza immunization should also be considered for household contacts of immunocompromised individuals.
Travellers belonging to the high-risk groups for influenza should be regularly vaccinated each year. Those travelling from one hemisphere to the other shortly before, or early during, the influenza season should obtain vaccination for the opposite hemisphere.
One dose is given I/M for individuals over 9 years of age. Two doses are given at least 4 weeks apart for immunocompromised people and for children aged between 6 months 9 years; those aged 6–36 months should receive half the adult vaccines injections. Annual immunization is recommended for individuals aged above 6 months suffering from ailments as mentioned above. |
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