Influenza Surveillance Update – Alicia Budd (CDC)
Alicia provided an update on influenza activity reported for week 16, ending April 20, 2019. Influenza activity continues to decline. In addition, the good news is that influenza-like illness (ILI) has now declined below the national baseline. (See further information on ILI below.)
For the week, ~8% of specimens sent to clinical laboratories tested positive for influenza. Because fewer influenza positive specimens are being received, there has not been a great change in the proportion of viruses by type, subtype, and lineage. Influenza A (H1) remains the predominant strain reported for the season, but, since mid/late February, H3 has been the most common virus reported. Looking at reports from recent weeks, all 10 regions are now H3 predominant. Region 4 is the only region that has been H3 predominant for the entire season. The amount of reported influenza B circulating viruses continues to remain very low, though the proportion has increased simply because the amount of A virus is decreasing.
During this season, >2,000 viruses have been genetically or antigenically characterized. As reported in previous weeks, all of the H1 viruses are the 6B1 clade, and almost all of these have been similar to the cell-propagated vaccine reference virus. Multiple clades and subclades of the H3 virus are co-circulating; the 3C3a subclade is by far the predominant subclade in the U.S. this season. Fifty-five (55) percent of the H3s are antigenically similar to the cell-grown reference virus representing the vaccine strain.
All of the Influenza B Yamagata viruses tested have belonged to the Y3 clade and are antigenically similar to the cell-grown vaccine virus. The majority (59%) of the B Victoria viruses are the V1A.1 clade, which is the same clade as the vaccine. Seventy-six (76) percent of the B Victoria viruses that have been tested are similar to the cell-propogated vaccine virus. More than 2,000 viruses have been tested for resistance to oseltamivir, peramivir, and zanamivir. A report for H1 virus specimens shows reduced or highly reduced susceptibility to oseltamivir and/or peramivir. A total of 35 H1 specimens have now been found to have reduced or highly reduced inhibition by oseltamivir and peramivir. No viruses have been identified with resistance to zanamivir.
Outpatient visits for influenza-like illness (ILI) declined to 2.1%, which is below baseline levels for the first time in 21 weeks. Six of 10 surveillance regions are below their region-specific baselines. On a state level, Puerto Rico experienced high ILI levels, 1 state reported moderate activity, and the remaining 49 states were either at low or minimal activity.
Cumulative reports to FluSurv-NET this season indicate a rate of 64/100,000 lab-confirmed influenza hospitalizations. Highest hospitalization rates were seen in persons >65 years at almost 214/100,000, followed by children 0–4 years at approximately 73/100,000. The percent of deaths reported due to pneumonia and influenza (P&I) was 6.6%. This is the second week in a row that reports have been below epidemic threshold levels.
Five (5) influenza-associated pediatric deaths were reported to CDC during this week, bringing the total to 96 for the season. Eighty-eight (92%) of these deaths were associated with influenza A virus infections, 7 with influenza B, and one (1) with an influenza B virus that was not typed. Of the influenza A viruses for which subtype information is available, 71% were H1 virus infections.
For the geographic spread of influenza during the week, 5 states reported widespread activity. Seventeen (17) states and Puerto Rico reported regional activity, and 28 states, the District of Columbia, and the Virgin Islands reported local or sporadic activity.
For the preliminary influenza burden reports released, an estimated 36.9 – 42.4 million persons have been ill with flu, 17-19.9 million have had a medical visit, and approximately 518,000 – 630,000 persons have been hospitalized. An estimated 35,600 – 59.500 flu-related deaths have occurred.
Other Items – L.J Tan (IAC)
- 2019 Summit In-Person Meeting – Register Now! – The 2019 Summit in-person meeting will be held in Atlanta, GA on May 14–16, 2019. The current agenda and registration Information are available on the 2019 National Adult and Influenza Immunization Summit webpage. (Please note that the password to register for this invitation-only meeting is available by contacting L.J Tan.) If possible, please book your room either through the onscreen “pop-up” that appears after you register or later through the email you receive after completing your registration. This not only will give you access to the “preferred rate,” it also will help the Summit meet its lodging contractual agreement with the hotel.
- Panel Discussion: Utility of Observational Real-World Evidence to Inform Vaccine and Public Health Decision-Making – Seqirus is sponsoring a dinner and panel discussion on May 14 in Atlanta. During the program, Utility of Observational Real-World Evidence to Inform Vaccine and Public Health Decision-Making, the panel will discuss the use of real-world evidence to help define how vaccine effectiveness is used to make decisions about influenza vaccines. The panel also will discuss how real-world evidence can be used to maintain confidence in the need for influenza vaccines. Panelists include: Mark Blatter, Claire Hannan, Arnold Monto, and Mitch Rothholz. While this meeting is being held in parallel with the Summit in-person meeting and at a location close to the Summit meeting, it is not associated with the Summit itself.