||On December 3, 2014, the CDC issued a health advisory regarding potential circulation of drifted influenza A (H3N2) viruses and need for antiviral medications. In past flu seasons when H3N2 predominated, greater overall and age-specific hospitalization rates and more mortality occurred. To date, H3N2 viruses have predominated this season, and data indicate that about half of those viruses have drifted antigenically from this year’s vaccine virus, suggesting possible decreased vaccine effectiveness. In response to detection of drifted influenza A (H3N2) viruses, CDC is reemphasizing the use of antiviral medications when indicated for treatment and prevention of flu, and as an adjunct to vaccination.
CDC also recently issued a statement in response to 2013-14 vaccine effectiveness data, which revealed that live, attenuated influenza vaccine (LAIV) showed no measurable effectiveness against influenza A (H1N1) among children. Those data are distinct from previous studies, which indicated that LAIV may be more effective than inactivated influenza vaccine (IIV) in younger children, and suggest that LAIV may not protect against H1N1 during the 2014-15 season. Current seasonal influenza surveillance data show there is little H1N1 circulation.
CDC has not changed its 2014-15 influenza vaccination recommendations.
- Flu vaccination is still the best protection against flu. People who have not been vaccinated yet should do so now it’s not too late.
- Even if the strains are not a perfect match, the vaccine may offer some cross protection and help people avoid severe illness, hospitalization or death if they do get sick.
- Prompt antiviral treatment is important, especially among patients with severe flu-like illness, are at higher risk for influenza complications, or who are hospitalized.
- Healthcare providers should NOT wait for confirmation of flu to begin antiviral treatment. Antiviral treatment works best when started within 48 hours of illness onset.
- Children who were vaccinated with LAIV do not need to be revaccinated.
CDC's influenza vaccination resources:
Other influenza vaccination resources: