Live and inactivated flu vaccines have similar effectiveness in adults

Image: PD/CDC

Key study points:

1.  Healthy adults receive similar protection from live and inactivated flu vaccines.

Primer: Influenza is of a significant cause of morbidity and mortality in the United States with annual death rates ranging from 3,000 to 50,000 patients each year.  Annual vaccination remains the primary defense against the spread of influenza.  Currently the United States uses two types of the annual vaccine: live attenuated influenza vaccine (LAIV) and trivalent inactivated influenza vaccine (TIV).  LAIV has consistently been shown to be superior to TIV in children and adolescents.  However, studies in adults have provided mixed results and neither LAIV nor TIV has consistently shown superiority.  Since vaccination against influenza is recommended for all adults, determining superiority of one vaccine over another is crucial.  The authors of this study compared outcomes in US military members who had received one of the two types of flu vaccines.

Background reading

1. The efficacy of intranasal live attenuated influenza vaccine in children 2 through 17 years of age: a meta-analysis of 8 randomized controlled studies.

2. Comparative efficacy of inactivated and live attenuated influenza vaccines.

This [retrospective cohort] study: took data from a large Department of Defense study on health behaviors (Millenium Cohort Study).  Data on healthy active duty service members were compiled for the flu seasons of 2006-2007, 2007-2008, and 2008-2009.  The primary outcomes of interest were Influenza like illness (ILI), confirmed influenza, and pneumonia.  A total of 41, 670 vaccination events were evaluated.  Multivariate analysis adjusting for multiple factors showed no significant difference in risk of ILI between LAIV and TIV.  Additionally, there was no significant difference in risk of influenza or pneumonia between the vaccine types.

In sum:  This study suggests that healthy adults benefit equally from the live attenuated and trivalent inactivated flu vaccines.  Limitations of the study include the fact that data was gathered from a pre-existing cohort of military service members, a population generally more healthy and fit than the public at large, and diagnoses were based on ICD-9 codes and office visits.  Additionally, since seasonal flu vaccination is required among all active duty personnel, the rate of circulating flu was likely much lower than it would be in a civilian population.  Taken together these results should reinforce the current guidelines regarding annual flu vaccination, and place the emphasis on vaccination itself rather than on the type of vaccine.

Click to read the study in CID

By [AS] and [MS]

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