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2008–2009 Influenza update: A better vaccine match

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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).


 

References

Last year, some people may have lost their faith in flu shots. The three antigens chosen for the vaccine in advance by the US Centers for Disease Control and Prevention (CDC) did not match very well the influenza strains that ultimately circulated in North America, and the overall protective efficacy of the vaccine was estimated at only 40%.

Nevertheless, vaccination remains the primary preventive measure for both epidemic and pandemic influenza, especially in view of a rising rate of resistance to the oral antiviral agent oseltamivir (Tamiflu).

In the 2008–2009 influenza season, we hope to do better. 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 be a good match for the strains circulating in the Northern Hemisphere. And with 146 million doses expected to be manufactured this season by six companies—the largest number of doses ever manufactured in the United States—enough should be available for all.

GREAT STRIDES HAVE BEEN MADE, BUT FLU IS STILL A PROBLEM

We are making great strides against influenza. Over the last 50 years, the rate of influenzarelated deaths in the United States declined by 95%, from an average seasonal rate of 10.2 deaths per 100,000 population in the 1940s to 0.56 per 100,000 by the 1990s. 1

However, influenza still accounts for about 10% of patients admitted to intensive care units for acute respiratory failure during epidemics. 2

Children and the elderly are still hit the hardest: infants age 0 through 23 months and adults age 65 years and older have the highest peak rates of pneumonia and influenza hospitalization and death. 3 School-age children (5–18 years) have an indirect role in anticipating the risk to others and can learn to help avoid spreading the virus by washing their hands more, wearing masks, and adopting other hygienic measures.

In the 1918–1919 pandemic, most deaths were from secondary bacterial pneumonia, a fact that has implications for pandemic preparedness. 4 Currently, Staphylococcus aureus , particularly methicillin-resistant strains (MRSA), is an important cause of secondary bacterial pneumonia, with a high mortality rate. 5

UPDATE ON DIAGNOSIS: PCR IS THE BEST TEST

In the hospital, it is important to identify patients who have influenza so that we can give them appropriate antiviral therapy and also protect other patients from getting the flu. Unfortunately, the sensitivity and positive predictive value of fever, cough, and other symptoms for the diagnosis of influenza in hospitalized patients are 40% or less. 6

Real-time reverse transcriptase polymerase chain reaction (PCR), compared with direct fluorescent antigen detection or cell culture, has the highest sensitivity (98.7%) and specificity (100%) in both children 7 and the elderly. 8 Furthermore, cell culture is slow and therefore is not useful in clinical practice. Nasopharyngeal wash sampling appears impractical in nursing home residents, owing to their underlying disabilities, and nasopharyngeal swabs tested by PCR are equally sensitive. 8

However, improvements are needed in molecular detection and subtyping of influenza viruses. 9 If a pandemic breaks out, we will need to identify the virus quickly to have enough time for preventive interventions. The US Food and Drug Administration has recently cleared a new test called the Human Virus Real-Time RT-PCR Detection and Characterization Panel to detect and differentiate between seasonal and novel influenza strains. 10

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