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

Figures & data

Table 1 Influenza A proteins

Protein	Function
HA	Receptor binding and release of viral genome. Most important antigenic protein. Trimeric structure.
NA	Second most important antigenic determinant. Tetrameric enzymatic protein and target for antiviral treatment.
M2	Tetrameric H+ ion channel and target for antiviral treatment
PB1, PB2, PA	Viral polymerase complex
NP	Nucleoprotein
M1	Structural matrix protein
NS1, NS2, PB1-F2	Regulatory proteins and RNA transport

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.

Table 2 Target groups for vaccination (WHO 2005)

1	Residents of institutions for the elderly or the disabled;
2	Elderly non-institutionalised individuals with 1 or more of the following chronic conditions, chronic cardiovascular, pulmonary, metabolic or renal disease, or who are immunocompromised;
3	Other individuals (adults and children aged >6 months) in the community who have chronic cardiovascular, pulmonary, metabolic or renal disease, or are immunocompromised;
4	Individuals who are above a nationally defined age limit irrespective of their medical risk status (most countries define the limit of age >65 years);
5	Other groups defined on the basis of national data such as those with frequent contact with high-risk persons, health care workers, pregnant women and children 6–23 months old.

Table 3 The efficacy of influenza vaccine in different population groups from representative studies

	Serum HI	Laboratory confirmed influenza	Hospitalization P&I	Death	References
Adults	83–90%	73–78%			Beyer 2002
Elderly, no other risk	37–86%	30–81%	33%	50–75%	Goevert 1994, Fleming 1995,Vu 2002, McElhaney 2005
Elderly, institution and non-institution		53%	50%	68%	Gross 1995
Elderly, chronic lung diseases			52%	45–70%	Nichol 1999
COPD patients	45–87%			45%	Wang 2006, Wongsurakiat, 2004

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