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CDC Committee Reaffirms Recommendation for Annual Influenza Vaccination

Advisors state no preference for flu shot or nasal spray

The Advisory Committee on Immunization Practices (ACIP) of the Center for Disease Control and Prevention (CDC) has voted on its annual influenza vaccine recommendations for 2015–2016. The ACIP voted to continue to recommend that all persons 6 months of age and older be vaccinated annually against influenza.

However, the committee did not renew its 2014–2015 preference for using the nasal spray flu vaccine (live attenuated influenza virus [ LAIV]) instead of the flu shot (inactivated influenza virus [IIV]) in healthy children 2 through 8 years of age when immediately available. The preferential recommendation was originally approved in June 2014, after a review of data from several influenza seasons suggested that the nasal spray vaccine could offer better protection than the flu shot for children in this age group.

The decision not to renew the preferential recommendation was made based on new data from more-recent seasons, which have not confirmed the superior effectiveness of LAIV observed in earlier studies. The ACIP recommends that children 6 months of age and older reveive an annual influenza vaccine with no preference stated for either the nasal spray or the flu shot.

The ACIP is a panel of immunization experts that advises the CDC. Part of the ACIP charter is to continually evaluate new data and to update or change recommendations as warranted. The new data considered by the ACIP included vaccine effectiveness (VE) estimates for 2013–2014 and for the current 2014–2015 season.

In October 2014, VE data for the 2013–2014 flu season were presented to the ACIP. These data showed no measurable effectiveness for LAIV against influenza A (H1N1) among children, whereas the IIV vaccine effectiveness mid-point estimate against H1N1 in children aged 2 through 8 years that season was 60% and was statistically significant. H1N1 was the predominant virus in circulation during the 2013–2014 season for the first time since it emerged in 2009 to cause a pandemic.

On February 26, 2015, interim data from the U.S. Flu VE Network were presented to the ACIP. The mid-point vaccine effectiveness estimate for IIV against H3N2 in children aged 2 through 8 years was 15% compared with –23% for LAIV. These data suggest that neither vaccine worked well in protecting against H3N2 viruses this season, and that the LAIV vaccine did not work better than the IIV vaccine against the predominant H3N2 viruses circulating during the current season. Limited data are available on the effectiveness of LAIV against drifted H3N2 viruses, but some studies had suggested that LAIV might offer better protection against such viruses.

Since 2010, the CDC and the ACIP have recommended that everyone 6 months of age and older receive a flu vaccine annually, with rare exceptions. Although a flu vaccine is the best way to prevent influenza infection, efficacy can vary. Since the CDC began measuring VE in 2004–2005, estimates have ranged from 10% to 60%.

One factor that can influence how well a vaccine works is the similarity between the vaccine viruses and circulating influenza viruses. More than two-thirds of the H3N2 viruses circulating nationally in the U.S. this season are different from the H3N2 vaccine virus; the proportion of drifted viruses is higher (greater than 80%) at U.S. VE Network study sites. Host factors of the person being vaccinated, such as age, health, and immune status, also can affect how well a vaccine works.

The ACIP recommendation must be adopted by the CDC Director. The recommendation would then be incorporated into the 2015–2016 influenza prevention and control recommendations and published in the CDC’s Morbidity and Mortality Weekly Report, at which point it would become official CDC policy.

Source: CDC; February 26, 2015.

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