The Centers for Disease Control and Prevention (CDC) recently announced that so far this year, the predominant strain of influenza causing disease is a drifted strain of the influenza A virus H3N2. As of early December, more than 91 percent of CDC-tested samples were influenza A strains and the balance were influenza B. Here is what you should know:
- Historically, H3N2-dominated influenza seasons have been more severe, causing higher rates of hospitalizations and deaths.
- H3N2-dominated seasons tend to be particularly severe for those groups at highest risk from influenza, including children, elderly adults, pregnant women and those with chronic conditions, such as heart- and lung-associated diseases.
- Although influenza vaccines contain an H3N2 strain of the virus, the circulating strain has drifted, such that to date, about 68 percent of H3N2 samples have been significantly different from the A/Texas/50/2012 strain included in the vaccine.
- The drifted strain is classified as A/Switzerland/9715293/2013. When the strain suggestions were made for the Northern Hemisphere, this strain was not often detected. However, increasing numbers of specimens caused the World Health Organization (WHO) to recommend its inclusion in the 2015 Southern Hemisphere vaccines.
- Although current influenza vaccines do not afford significant protection against the drifted strain, they contain two or three other strains and are the best opportunity to prevent influenza infections, so should still be encouraged.
- Additionally, patients, especially those in high-risk groups, should be encouraged to seek treatment early for influenza-like illness since anti-virals can decrease the severity of disease if started early in infection.
- By the beginning of December, seven pediatric deaths have been attributed to influenza.
Resources related to this situation
Resources related to influenza in general
Check these resources for general information related to influenza: