Influenza Surveillance Update – Alicia Budd (CDC)
Alicia provided an update on influenza activity reported for week 10, ending March 9, 2019. Influenza activity continues to be elevated, but it has decreased slightly from the prior week.
For the week, 25.8% of specimens sent to clinical laboratories tested positive for influenza. This is a slight decrease from the percentage reported during the previous week. Influenza A (H1) remains the predominant strain reported, but the proportion of H3 reports is increasing. Looking at reports from the last three weeks, 7 regions are now H3 predominant, compared to 5 regions as reported during last week’s Summit call. 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.
During this season, more than 1,400 viruses have been genetically or antigenically characterized. As reported in previous weeks, all of the H1 viruses are the 6B1 clade, and 98% of the antigenically characterized H1 viruses were similar to the cell-propagated vaccine reference virus. Multiple clades and subclades of the H3 virus are co-circulating, with the 3C3a subclade continuing to increase. At 60%, this is the predominant subclade in the U.S. this season. Sixty-two percent (62%) of the H3s are antigenically similar to the cell-grown reference virus representing the vaccine strain. Most of the H3s that had low similarity to the cell-grown reference virus belong to clade 3C3a.
All of the Influenza B Yamagata viruses tested have belonged to the Y3 clade and are similar to the cell-grown vaccine virus. Co-circulation of several Victoria viruses is occurring, but the majority (82%) belong to the V1A.1 clade. Eight (8) triple deletion Victoria viruses have been reported this season. Almost 1,500 viruses have been tested for resistance to oseltamivir, peramivir, and zanamivir. All viruses tested showed susceptibility to zanamivir, and more than 99% displayed susceptibility to oseltamivir and peramivir. Four H1 specimens have been found to have reduced or highly reduced inhibition by oseltamivir and peramivir. Susceptibility testing also is being performed on balaxovir, but CDC has nothing to report on this yet. Alicia noted that the amount of balaxovir currently being used in the U.S. is relatively low, so we wouldn’t expect to see much resistance. However, CDC will report immediately if anything concerning is seen. Balaxovir susceptibility will be included in routine reporting beginning next season.
Outpatient visits for influenza-like illness (ILI) declined to 4.5%. This is the third week in a row in which a decline has been experienced. Despite this decline, ILI activity is still elevated and has been at or above baseline nationally for 16 consecutive weeks. All 10 surveillance regions are above their region-specific baselines. Three regions are reporting increasing ILI activity, while the remaining regions are seeing declines, some for multiple weeks in a row. On a state level, 30 states experienced high ILI levels, 11 states reported moderate activity, and the remaining 9 states and New York City, the District of Columbia, and Puerto Rico were at low or minimal activity levels.
Cumulative reports to FluSurv-NET this season indicate a rate of 41.3/100,000 lab-confirmed influenza hospitalizations. Highest hospitalization rates were seen in persons >65 years at almost 124/100,000, followed by the 0–4 age group at approximately 54.8/100,000. The 50–64 year age group reported a rate of 54/100,000.
The percent of deaths reported due to pneumonia and influenza (P&I) was 7.2% during the week ending March 2, slightly below the epidemic threshold for this week. P&I has been relatively low for the entire season.
Sixty-eight (68) influenza-associated pediatric deaths were reported to CDC this season. Of these 64 were associated with influenza A virus infections, 3 with an influenza B virus infection, and 1 with an influenza virus that wasn’t typed. Eighty percent (80%) of the A viruses with subtype information available were H1, and 20% were H3.
For the geographic spread of influenza during the week, 46 states and Puerto Rico reported widespread activity. Four (4) states reported regional activity, and the District of Columbia reported low activity.
For the preliminary influenza burden reports released, an estimated 25.5–29.3 million persons have been ill with flu, and approximately 327,000–394,000 were hospitalized. An estimated 21,500–35,500 persons have died.
The WHO vaccine strain selection decision for the 2019–2020 season for the Northern Hemisphere was delayed this year. In February, the group chose to maintain the current B Yamagata and B Victoria strains in the vaccine, as well as to update the H1 component to a more recent H1-pdm09 virus. However, the group chose to delay a decision on the H3 vaccine component until more current data could be reviewed. On March 21, the group decided to update the H3 component to a 3c3a virus, A/Kansas/14/2017 (H3N2)-like virus. The FDA’s Vaccines and Related Biological Products Advisory Committee will meet on March 22 to finalize this decision for the U.S.
Other Items – L.J Tan (IAC)
- 2019 Summit In-Person Meeting Information Now Available Online – The 2019 Summit in-person meeting will be held in Atlanta, GA on May 14–16, 2019. Information on registration is 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.