Influenza is an acute viral respiratory illness. It is characterised by the sudden onset of symptoms, which include a temperature of 38° Celsius or more with a dry cough, headache, sore muscles and sore throat. The cough is often severe and protracted, but otherwise the disease is self-limiting. While those who are in good health usually recover from influenza in two to seven days, there are others for whom the disease is much more severe. In those with underlying diseases, especially the elderly, complications are common and hospitalisation rates are high.
Many respiratory diseases occur every winter but influenza is one of the most severe. There are three types of influenza virus, A, B and C. Influenza A and influenza B cause the majority of infections, with influenza A generally causing the most severe form of the disease. The third type, influenza C, is rarely reported as a cause of human illness.
Constant genetic changes in influenza viruses mean that the vaccines' virus composition must be adjusted annually to include the most recent circulating influenza A(H3N2), A(H1N1) and influenza B viruses. The WHO's global influenza surveillance network writes the annual vaccine recipe. The network, a partnership of 112 national influenza centres in 83 countries, is responsible for monitoring the influenza viruses circulating in humans and rapidly identifying new strains. Based on information collected by the network, the WHO recommends annually a vaccine that targets the three most virulent strains in circulation.
On 13 February 2004, the WHO published its recommendation on the composition of influenza vaccines for use in the 2004-05 northern hemisphere influenza season. The recommendation was as follows:
A/New Caledonia/20/99(H1N1)-like virus
A/Fujian/411/ 2002(H3N2)-like virus*
*The currently used vaccine virus is A/Wyoming/3/2003. A/Kumamoto/102/2002 is also available as a vaccine virus.
**Candidate vaccine viruses include B/Shanghai/361/2002 and B/Jilin/20/2003, which is a B/Shanghai/361/ 2002-like virus.
The National Disease Surveillance Centre, NDSC, in partnership with the Irish College of General Practitioners, ICGP, and the Virus Reference Laboratory, VRL, have established a network of computerised general sentinel practices which report on a weekly basis the number of patients seen with influenza-like illness. As there is little difference in the presenting symptoms of a number of respiratory pathogens, virological confirmation is required to identify that influenza is the causative agent. The VRL can detect and identify if influenza A and-or B viruses are circulating. Following collection of the data, a weekly influenza report is compiled by the NDSC. Reports of influenza activity in Europe and worldwide are also provided as part of the overall monitoring of influenza activity. The report is produced every Thursday throughout the influenza season, which runs from October to May.
The first report for this season was published on 7 October and stated that influenza activity was at a low level in Ireland. The second report published on 14 October noted that influenza activity remained at low levels. One case of influenza A virus was reported in the first week, the only case of influenza reported so far this winter.
The impact of the influenza vaccine in reducing mortality from influenza in older people is well documented. Protection lasts about one year and, therefore, it is important that individuals who are at risk of contracting influenza are vaccinated annually against the current strains. Notwithstanding a problem with one supplier that affected supplies worldwide, ample supplies of flu vaccine have been secured for Ireland. Some 200,000 doses of flu vaccine were distributed around the country in early September, a further 192,680 doses were distributed during the first week in October and another 200,000 doses will be delivered later this month. This compares favourably with last year when approximately 470,000 doses of vaccine had been distributed by the middle of November.
The vaccine is available free of charge from general practitioners to medical card holders who are deemed to be at risk of serious illness as a result of contracting the disease. Persons in the at risk group who do not have a medical card can obtain the vaccine free of charge. However, the fee for administering the vaccine in such cases is a matter between the general practitioner and the patient. The at risk group includes persons aged 65 years or older, those with specific chronic illness such as chronic heart, lung or kidney disease, and those with a suppressed immune system. For persons in the at risk group, complications arising from influenza such as pneumonia are common and can be fatal, particularly in the elderly.
My Department asked health boards on 23 September last to advise general practitioners to concentrate their efforts on ensuring that patients at greatest risk receive priority vaccination. A national and local media campaign is planned by the Health Boards Executive to take place at the beginning of November in order to remind those who are in the at risk group and who have not yet received the vaccine to do so immediately.