CDC Health Advisory Regarding the Potential for Circulation of Drifted Influenza A (H3N2) Viruses

Abstract

This season’s influenza surveillance reveals that a significant number of infections are due to strains not covered by the vaccine, an important observation for transplant recipients who are at increased risk for complications from influenza infection. This season’s influenza surveillance reveals that a significant number of infections are due to strains not covered by the vaccine, an important observation for transplant recipients who are at increased risk for complications from influenza infection. In lieu of this month’s MMWR selection, we have chosen to present a CDC Health Advisory (http://emergency.cdc.gov/han/han00374.asp) (1.CDC Health Advisory Regarding the Potential for Circulation of Drifted Influenza A (H3N2). Viruses http://emergency.cdc.gov/han/han00374.asp. Distributed December 3, 2014.Google Scholar) related to the potential for circulation of influenza A viruses that are not covered by the current influenza vaccine. Each year, the specific influenza strains that will comprise the annual vaccine are selected based on the worldwide epidemiologic assessment of the patterns and prevalence of circulating flu strains, and on whether the current vaccine provides appropriate coverage for the predominant circulating strains. Surveillance during influenza season determines whether or not the vaccine covers the circulating strains in a given year. Although influenza most commonly occurs during the winter months, early cases of influenza can provide some surveillance data to inform the degree to which circulating strains are covered by the current vaccine. Based on the epidemiology of influenza from October 1 through November 22, 2014, H3N2 influenza A strains have been the predominant influenza strains observed in the United States. This is notable as H3N2 influenza A strains have been associated with higher overall age-specific hospitalization rates and greater mortality, especially in the very young, the elderly, and those with chronic medical conditions (including transplant recipients). This season, 52% of the circulating H3N2 influenza A strains are antigenically distinct from the H3N2 strain that is included in the vaccine. In previous seasons, when the virus has drifted (been antigenically different), the effectiveness of the vaccine has been diminished. Nevertheless, the vaccine may still afford some protection against these viruses, as there may be cross-protection against the drifted viruses. This may result in a reduction in the incidence of severe outcomes, even if infection is not fully prevented. Additionally, because multiple influenza strains may be circulating during this season, the vaccine may still afford protection against other strains (e.g. the influenza A H1N1 and influenza B strains), which may be included in the vaccine composition. Because of this the Centers for Disease Control and Prevention have recommended the following:•Individuals who are ≥6 months of age who have not yet been vaccinated should undergo influenza vaccination to decrease the overall burden of influenza and potentially ameliorate the severity of influenza due to cross-protection.•Transplant recipients should only receive injectable vaccine.•Any individual who develops influenza-like symptoms and who is at high risk for complications should promptly seek medical attention to determine if antiviral therapy is indicated.•Typical symptoms include fever, cough, sore throat, runny or stuffy nose, myalgias, headache, fatigue, and occasionally vomiting and diarrhea.•Treatment should be considered for high-risk individuals with consistent symptoms, with initiation of therapy prior to laboratory confirmation of influenza.•Patients on immunosuppression, including transplant recipients, are among those considered to be at increased risk for complications•Other high-risk individuals include people <2 years or ≥65 years; those with chronic pulmonary, cardiovascular, renal, hepatic, hematological, and metabolic disorders; those with neurologic/neurodevelopmental conditions; pregnant or early postpartum women; people <19 years on chronic aspirin; American Indians; Alaskan Natives; individuals with BMI ≥40; and residents of nursing homes and chronic care facilities.•Preferred treatment options are oseltamivir for any individuals ≥2 weeks and zanamivir for individuals ≥7 years in age.•Antiviral prophylaxis is recommended with institutional outbreaks or for people with contraindications to influenza vaccine.•Options for prophylaxis are oseltamivir for individuals ≥1 year and zanamivir for those ≥5 years in age.•When used as prophylaxis, antivirals should be given for at least 2 weeks and continued for at least 7 days after identification of the last known case in an outbreak.•Additional preventive health practices that should be followed to decrease influenza transmission include•Respiratory hygiene/cough etiquette•Social distancing•Hand washing Additional information about influenza can be found on the CDC website: http://www.cdc.gov/flu/.