A Paradigm for the Control of Influenza
In this issue of the Journal, Glezen et al have produced the latest in a series of descriptions of an innovative approach to the control of influenza. Dr Glezen and colleagues at Baylor College of Medicine have long been advocates of the concept that the epidemiology of influenza is the most important element in the control of this disease.
The study by Glezen and colleagues investigates the effectiveness of immunizing 47.5% of elementary‐school children 5–11 years old in 25 public schools and 3 parochial schools in which 1 dose of live attenuated influenza vaccine (LAIV) was administered (intervention group), relative to a comparable community in which vaccine (LAIV or trivalent inactivated vaccine [TIV]) was administered in an off‐protocol manner. A significant degree of herd protection (reduction in the number of medically attended acute respiratory illness [MAARI]) was seen in all age groups except 12–17‐year‐olds, with risk ratios for all age groups >18 years old being lower even than that for the target group of 5–11‐year‐olds. This occurred despite there being an excess of persons >75 years old in the intervention community. Furthermore, LAIV was 1.7 times more effective in the prevention of proven influenza virus infection in the target group than among those who received TIV and was 6 times more effective than among those who did not receive vaccine.
Preschool and school‐age children are the major disseminators of influenza. They have the highest age‐specific attack rates for influenza, are less likely to observe cough and sneeze precautions, and are in close proximity to each other and family members. Furthermore, they excrete influenza A virus longer before becoming ill (6 days vs 1 day) and after illness appears (14 days vs 4.5 days), compared with adults. They are centrifugal spreaders to family members, other children, and individuals in the community, including those at high risk.
Serious morbidity from influenza is increasing, and the negative effect on human life and the economy ($87 billion per year) is considerable. Previous efforts to control influenza have concentrated on immunizing populations—for example, elderly persons, those medically at risk, and young children. This approach has fallen far short of the targets determined by the Healthy People 2010 initiative. One of the at‐risk groups that has been demonstrated to be at particularly high risk of H1N1/09 infection—pregnant women—has been underimmunized historically. In one study conducted during the 2007–2008 influenza season, only 24% of pregnant women were immunized, the most common reason given being “MD did not mention”. Historically, the group at highest risk is individuals >65 years old, who frequently exhibit immune senescence. Simonsen et al reported no significant effect of influenza vaccine on seasonal mortality among elderly persons. Furthermore, despite an increase in the vaccination rate among individuals >65 years old between 1989 and 1997, mortality and hospitalization rates continued to increase, suggesting that administering vaccine to this group is not very effective. This notion is supported by the work of Jackson et al, who observed that those who take the vaccine are in better health and are more mobile; therefore, they are more able to receive the vaccine than their sicker counterparts. This has led to an overestimation of the effectiveness of influenza vaccine in this highest‐risk age group and may, in part, account for the observation of increasing morbidity and mortality among elderly persons in the face of increasing vaccine use.