2008–2009 Influenza update: A better vaccine match
ABSTRACTLast year, the influenza vaccine did not match the circulating strains very well, and its overall protective efficacy was only 40%. All three antigens contained in the 2008–2009 vaccine are new. Surveillance data from the Southern Hemisphere during the summer of 2008 show that this vaccine is expected to match well the circulating strains in the Northern Hemisphere.
KEY POINTS
- Real-time reverse transcriptase polymerase chain reaction is the most accurate and clinically useful diagnostic test for influenza.
- All children age 6 months to 18 years should be vaccinated, and the live-attenuated vaccine is now approved for use in children 2 years old and older.
- We should continue to pursue traditional and innovative measures to increase influenza vaccination rates.
- Influenza vaccination during pregnancy reduces laboratory-confirmed influenza in infants up to 6 months of age by 63%.
- Hygienic measures (particularly hand-washing) aimed at younger children can prevent the spread of respiratory viruses in the community.
- Primary viral resistance to oseltamivir (Tamiflu) is rising, but almost all isolates remain susceptible to zanamivir (Relenza).
More people are being vaccinated, but we’re still below our goals
Although influenza vaccination rates among adults continue to improve,18 they remain well below the Healthy People 2010 initiative’s target of 90% in adults age 65 and older (the current rate is 72%) and below the target of 60% in people age 18 through 64 who have one or more high-risk conditions, health care workers, and pregnant women19 (currently 35% in people age 18 through 49 and 42% in people age 50 through 64). Thus, we still need to improve vaccination coverage rates.
Health care providers should offer vaccination at every opportunity between October and May.20 Offering vaccination in nontraditional settings such as work sites and pharmacies is likely to be cost-saving for healthy adults due to averted morbidity.21 At many hospitals, health care workers can opt out of being vaccinated, but they must formally state that they are doing so. The use of these declination statements among health care workers is associated with a mean increase of 11.6% in vaccination rates.22
Since influenza is the second most frequent vaccine-preventable infection in travelers, the vaccine should be offered to those crossing to the opposite hemisphere during its peak influenza season (eg, to South America in May through September), as well as to those visiting the tropics at any time of year.23
Vaccination is safe and effective in high-risk groups
Data on vaccination are reassuring in several at-risk groups.
In pregnancy, there is no indication that infants are harmed if their mothers are vaccinated in the first trimester.24 The evidence of excess morbidity during influenza epidemics supports vaccinating healthy pregnant women in the second or third trimester and those with comorbidities any time during pregnancy. Influenza vaccination during pregnancy reduces laboratory-confirmed influenza in infants up to 6 months of age by 63% and prevents 29% of all febrile respiratory illnesses in infants and 36% of those in mothers.25
In patients with chronic obstructive pulmonary disease, vaccination cuts the rate of outpatient visits and hospitalizations due to acute respiratory illness by 67%.26 The antibody response to influenza vaccine in patients with rheumatoid arthritis treated with rituximab (Rituxan), a monoclonal antibody directed against CD20 surface antigen-positive B lymphocytes, was lower than in healthy controls, but was not negligible.27
Dispelling myths about vaccination in children
One recently published study in children younger than 5 years did not find vaccination to be effective in preventing influenza-related hospitalizations and outpatient visits.28 However, in both seasons in which this study was conducted, there was a suboptimal antigenic match between vaccines and circulating strains. Moreover, about 60% of participants were unvaccinated and another 20% were only partially vaccinated, making it difficult to assess vaccine effectiveness. Several other studies have shown that, when there is a good match, vaccine effectiveness in children is 85% to 90%.
Even though the live-attenuated (inhaled) vaccine is more expensive than the inactivated (injected) vaccine, it reduces the number of influenza illness cases and lowers subsequent health care use in children and productivity loss in their parents, with a net total savings of $45.80 relative to the inactivated vaccine.29 The live-attenuated vaccine provides sustained protection against influenza illness for 12 months following vaccination, as well as meaningful efficacy through a second season without revaccination, although at a lower level.30
Several myths about the live-attenuated vaccine should be dispelled.31 It is well tolerated and causes only mild, transient symptoms of upper respiratory infection, even in people with asthma or the early stages of human immunodeficiency virus infection. Genetic reversion of the vaccine strain to a wild-type virus requires independent mutation in four gene segments, an event that has not been observed. Finally, although viral shedding is common for several days after vaccination, transmission to another person has been shown in only one person, who remained asymptomatic.
Unfortunately, rates of influenza vaccination are even worse for children than for adults.32 In children 6 through 23 months old, only 22% are fully vaccinated; in those 24 through 59 months old, only 16.5% are.
One group of immunocompromised children, liver transplant recipients, achieved antibody seroprotection and seroconversion rates similar to those achieved by their healthy siblings, with no vaccine-related serious side effects.33 As in adults, the cell-mediated immune response to the vaccine was diminished, suggesting that other strategies are needed to provide optimal protection.
