Influenza: the virus and prophylaxis with inactivated influenza vaccine in "at risk" groups, including COPD patients

Abstract

Influenza is a major respiratory pathogen, which exerts a huge human and economic toll on society. Influenza is a vaccine preventable disease, however, the vaccine strains must be annually updated due to the continuous antigenic changes in the virus. Inactivated influenza vaccines have been used for over 50 years and have an excellent safety record. Annual vaccination is therefore recommended for all individuals with serious medical conditions, like COPD, and protects the vaccinee against influenza illness and also against hospitalization and death. In COPD patients, influenza infection can lead to exacerbations resulting in reduced quality of life, hospitalization and death in the most severe cases. Although there is only limited literature on the use of influenza vaccination solely in COPD patients, there is clearly enough evidence to recommend annual vaccination in this group. This review will focus on influenza virus and prophylaxis with inactivated influenza vaccines in COPD patients and other "at risk" groups to reduce morbidity, save lives, and reduce health care costs.

Figure 1

Schematic figure of influenza virus. On the surface of the virus there are three viral proteins, haemagglutinin (HA), neuraminidase (NA) and the matrix 2 protein (M2). Underlining the viral envelope is the matrix 1 protein (M1), the nucleoprotein (NP) encapsidates the genome segments with one complex of the polymerase attached (PB1, PB2 and PA). The non-structural protein 2 (NS2) is also contained in the virion in low numbers.

Figure 2

A simplified overview of the ecology of influenza A virus. The subtypes that have been detected in each species are shown and the subtypes marked in bold are the highly pathogenic avian influenza subtypes that have caused illness in humans. The main reservoir of influenza A viruses is waterfowl, which may carry highly pathogenic subtypes of influenza without visible illness. The H5N1 has also been detected in domestic cats, however, little is known about their role in H5N1 epidemiology. Currently, we do not have enough knowledge about the importance of migratory birds in the spread of influenza virus (hence the question mark). Interested readers can consult the reviews by Webster et al 1992 or Murphy et al 1996 for further information.