Influenza Surveillance Update – Alicia Budd (CDC)
Alicia provided an update on influenza activity for Week 52, ending December 29, 2019. Flu activity is high and is continuing to increase across the country.
Clinical labs reported 26% of submitted specimens were positive for influenza. This is similar to peak weeks seen in previous influenza seasons. However, it is too early to say whether we have reached the peak for the 2019–2020 season. Week 52 reporting is frequently affected by the Christmas season. We will need to wait on reports from ensuing weeks to determine if flu activity is actually going up or down. In the interim, it is safe to say that flu activity is widespread.
Public health labs reported widespread influenza with a mixture of strains among B Victoria (the most commonly reported), H1, and H3. Although there are some variations between regions, B Victoria is the predominant strain reported from all 10 regions. A few regions that were the earliest reporters for B Victoria are now seeing some movement toward increasing H1 reports. Strain differences continue to be seen among different age groups. Overall, for persons 0–24 years of age, B Victoria is predominant, while H1 is reported more frequently in persons 25 and older. Alicia noted that it is unusual for persons 65+ to be predominantly H1, but this is probably impacted by the fact that so little H3 is currently circulating. This continues to be a fluid situation; the best information on both regional and individual state activity is available on FluView Interactive.
Genetic characterization of influenza viruses continues to increase. All H1 strains tested were from clade 6B.1A and were similar to the cell-grown reference virus. Characterized H3 viruses belonged to the 3C.2a1 clade/subclade, which varies from the 3B.3a clade used in the vaccine. In spite of this antigenic difference, 34% of viruses characterized were similar to the vaccine strain. For B Victoria, 11% of specimens were double deletion viruses, while 89% were triple deletion viruses. Fifty-eight percent (58%) of B viruses were similar to the cell-grown reference virus. Of the more than 700 viruses tested, 99% were susceptible to the antiviral medications oseltamivir, zanamivir, peramivir, and baloxavir. Only 1 H1 specimen was found to be resistant to oseltamivir and zanamivir, and 1 B Victoria specimen was resistant to zanamivir.
Outpatient influenza-like illness (ILI) activity was at 6.9%, similar to the peak in the 2017–2018 season. However, this may have been influenced by changes to healthcare seeking activity around the holidays.
All 10 regions reported levels above baseline rates. State ILI activity also was high, with 37 states reporting high levels of influenza.
Although lots of influenza is circulating, severity indicators are not unusually high. Cumulative hospitalization rates are similar to other seasons, at 9.2 per 100,000 for the overall population. Highest rates are seen in age 65 and above (19.9 per 100,000), followed by the 0–4 year age group (17.8 per 100,000.) Rates of reported pneumonia and influenza (P&I) are still below threshold levels for the season. Alicia theorized that we might not be seeing as much severe illness because the circulating strains do not typically affect the elderly as much as other strains.
Five (5) influenza-related pediatric deaths were reported during the week, bringing the 2019–2020 total for pediatric deaths to 27. Eighteen of these deaths were associated with influenza B and 9 with influenza A. Of the 5 B viruses for which lineage was determined, all were B Victoria. All four of the influenza As which were subtyped were A(H1N1)pdm09 viruses.
Forty-five (45) states reported widespread influenza activity. In-season burden of influenza estimates are 6.4 million persons infected, 55,000 hospitalizations, and 2,500 deaths.
Other Items – L.J Tan
- 2020 Summit Meeting – This year’s meeting will be held on May 18, the day prior to the opening of the National Immunization Conference. Information on registration and other pertinent details is available on the Summit website. Approaching deadlines of importance are: nominations are being accepted for the 2020 Immunization Excellence Awards through February 1, and the deadline for a poster submission is March 15.
- NFID Annual Conference on Vaccinology Research (ACVR) – The ACVR is a well-established forum for the exchange of the latest scientific and clinical knowledge in vaccinology. The 2020 event will be held on March 23–25 in Washington, DC. Information about the conference and online registration is available on the NFID website..
- Summit Call Schedule – L.J reminded partners that Summit calls are held each Thursday at 3 pm ET unless otherwise cancelled via an email announcement.