Stage 2 replication transcription Stage 5 endocytosis Endosome Stage 3 nucleus Ribonucleoprotein Figure 1 Inﬂuenza virus cycle. Abbreviations: RNA, ribonucleic acid. Stage 1 RNA Stage 4 Stage 7 packaging Viral envelope Viral RNA Nucleoprotein Preventing inﬂuenza in COPD Influenza virus ribosome translation Viral proteins Stage 6 Cell membrane maturation Golgi apparatus Stage 8 Release of influenza virus reason, people can get ﬂu more than once and it is necessary to adapt the inﬂuenza vaccine to the minor changes detected during the inﬂuenza season in the inﬂuenza viruses. Inﬂuenza occurs worldwide. In temperate climates it appears in the winter, but it can occur any time during pan- demics. In the tropics inﬂuenza is endemic. Inﬂuenza caused by inﬂuenza A viruses are more frequent than those caused by type B possibly because of the slower rate of antigenic variation in inﬂuenza B. Inﬂuenza has a death-to-case rate of 1–2 deaths per 2000 cases (Harper et al 2005). Inﬂuenza viruses are spread from person to person through the coughing and sneezing of infected persons. The incubation period for inﬂuenza is 1 to 4 days, with an average of 2 days. Infected individuals are infectious from the day before symp- toms begin until approximately 5 days after onset of illness. Primary inﬂuenza illness is characterized by the abrupt onset of respiratory and constitutional symptoms, including fever, headache, severe tiredness, dry cough, sore throat, muscle aches, and runny or stuffy nose. Stomach symptoms International Journal of COPD 2007:2(1) such as nausea, vomiting, and diarrhea can occur, but they are more common in children than adults. Fever usually ranges between 38ºC and 40ºC. Fever is often higher in children than in adults, while it may be absent in the elderly. Inﬂuenza illness typically resolves after 3 to 5 days, although cough and tiredness can persist for more than two weeks. Complications of the acute inﬂuenza infection include: 1) primary viral pneumonia; 2) secondary bacterial pneu- monia; 3) other secondary bacterial infections, including bronchitis, sinusitis, and otitis; 4) exacerbation of a COPD; and 5) exacerbation of an underlying heart disease. The characteristic and uniformly observed lesion of inﬂuenza is necrosis of the cilial epithelium in the upper and middle portions of the respiratory tract. Pathological ﬁndings of complicated pneumonia are those characteristics of their causative agent (Cox and Subbarao 1999). In patients with primary inﬂuenza pneumonia, the lungs are airless, heavy with sanguineous edema, and mottled by subpleural hemorrhages. Bilateral interstitial inﬁltrates can be seen on chest radiography, 43