February 20, 2018 Volume 7

Influenza Activity Expected to Continue for Several More Weeks; It’s Not Too Late to Vaccinate!

Current Situation:  Influenza activity significantly decreased from week 1 through week 4; however, a slight increase in activity was observed over the past two weeks. Influenza activity is expected to continue through May and Orange County residents are encouraged to be vaccinated if they still haven’t received the 2017-18 vaccine. To date, 74 severe cases of influenza (less than 65 years of age and hospitalized in intensive care or who died) have been reported in Orange County; 12 of the 74 severe cases were influenza-associated deaths. Influenza A(H3) overall has been the most frequently identified influenza virus but A(H1N1) and B strains have also been reported.  Of note, the proportion of influenza reports that are type B (blue bar in graph) has increased over the past few weeks.

Secondary bacterial infections may complicate influenza: Influenza infection may be complicated by bacterial super-infection, most commonly with Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus (including MRSA), or Group A Streptococcus (GAS, S. pyogenes).  Of note, Orange County has had several severe GAS cases reported recently, complicating influenza-like illness (ILI) episodes in children. Others around the country have anecdotally reported similar events. Clinicians taking care of patients with ILI should consider secondary bacterial infection, especially in patients who seem to be improving and then worsen, or in patients who are severely ill.

Influenza Interim estimates of 2017-2018 season influenza vaccine effectiveness:   According to the CDC, overall vaccine effectiveness (VE) against medically-attended, laboratory confirmed illnesses from influenza was 36% thus far this season. VE was estimated to be 25% against illness caused by influenza A(H3) virus, 67% against A(H1N1)pdm09 viruses, and 42% against influenza B viruses. In addition, VE was higher (59%) among children aged 6 months to 8 years of age. Even with current vaccine effectiveness estimates, vaccination will prevent influenza illnesses, including thousands of hospitalizations and deaths. Recommendations: Continue to vaccinate persons aged ≥ 6 months of age against influenza who have not yet been vaccinated this season. Children 6 months to 8 years of age who did not receive at least two doses of influenza vaccine prior to 7/1/2017 need two doses this season, spaced 28 days apart. Persons who have already been ill with influenza this season should still be vaccinated as there are several strains circulating. Start antiviral medications ASAP in patients with symptoms of influenza who are hospitalized, severely ill, or at increased risk for complications. https://www.cdc.gov/mmwr/volumes/67/wr/mm6706a2.htm?s_cid=mm6706a2_e

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