A summary of presentations from the weekly Summit partner webinars

March 24, 2022 – The latest Summit summary

Flu Surveillance Update – Alicia Budd (CDC)

Alicia Budd, MPH, Influenza Division, CDC, gave an update presentation on CDC’s flu surveillance from FluVIew ending on March 12, 2022 (week 10).

Influenza Virologic Surveillance – U.S., 10/3/21–3/12/22:

There has been increasing flu activity for the past six weeks. The percent positivity is now higher than it was toward the end of last year when the last peak in flu activity occurred. However, both peaks are nowhere near what is expected in terms of peak activity that has been seen in previous years.

Genetic characterization: The U.S has predominately influenza A H3N2 viruses belonging to the 3C.2a1b clade and the 2a.2 subclade, which is what has been circulating all season. There is still a small amount of influenza B (Victoria) viruses circulating.

Antigenic characterization: There have been a few additional viruses tested, but the picture is the same in that the influenza A H3N2 viruses are not antigenically similar to the vaccine viruses. Of the influenza B (Victoria) viruses, about 80% are similar to the vaccine viruses.

The antigenic data is an indicator of how the vaccine might work in people. There is preliminary vaccine efficacy (VE) estimate data in the MMWR. [Published March 11. 2022].  This data is looking at the VE against medically attended respiratory illness in an outpatient setting. The data shows that there is not a lot of protection against outpatient medically attended respiratory illness. There are not enough cases to break down the data by age or investigate the influenza B (Victoria) viruses, therefore data will have to be analyzed later in the season.

Despite the low vaccine effectiveness estimates for the influenza A H3N2 viruses, CDC continues to recommend flu vaccination. There is a growing body of evidence that the vaccine can prevent serious outcomes even if it’s not able to prevent initial infection. There has also been an increase in flu activity again, and in the past seasons we have had a second wave of activity due to influenza B. There is no indication of influenza B activity picking up, but it is possible later in the spring.

Antiviral resistance: There has not been any antiviral resistance identified so far.

Outpatient Visits for Respiratory Illness, Reported by the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet):   Influenza-like illness (ILI) refers to someone who has a fever and cough or sore throat and could be caused by a number of respiratory viruses, including flu and SARS-CoV-2. There has been a slight increase over the past few weeks in the percent of outpatient visits for ILI. Individuals in the age 0–4 and age 5–20 groups are having the increase in activity, whereas the older age groups are remaining stable.

ILI Activity Level, Determined by Data Reported to ILINet, Week ending March 12, 2022 (Week 10): During week 10, there has been low to minimal activity, with a few states reporting moderate to high activity. ILI visits with similar symptoms can be caused by a variety of viruses, however in these hot spots of activity the majority of ILI is caused by the flu instead of COVID-19 or other illnesses.

Percent of Long-Term Care Facilities (LTCF) with at least One Confirmed Influenza Case among Residents, Reported to CDC’s National Healthcare Safety Network (NHSN), National Summary, 10/4/21–3/12/22:  The number of LTCF reporting at least one flu positive case among their residents has increased slightly.

Influenza hospitalizations in the U.S.: HHS Protect shows that over the past few weeks flu-positive admissions have been increasing. Cumulative influenza-associated hospitalization rate from FluServNet shows that flu activity is increasing but still low compared to what has been seen in prior years.

Influenza-related mortality data, U.S.: The percentage of death certificates that list pneumonia, influenza, or COVID-19 (PIC) as the cause of death has been declining quite significantly in the past few weeks, which is being driven by COVID-19. Flu still makes up a very small number of the deaths. There have been 13 pediatric deaths this season, all of which were tested positive for influenza A H3N2 viruses.

International Influenza Activity, Number of Influenza Positives Reported to WHO’s FluNet, 10/2018–3/12/22: Flu positive activity reported to the WHO shows that influenza A H3N2 is predominate worldwide except in China where influenza B (Victoria) is the dominate virus. There is an increase in flu activity in the northern hemisphere in general and the southern hemisphere has some unusual flu activity, but currently it’s mild.

Highly Pathogenic Avian Influenza (HPAI) A(H5N1): Current Situation in the U.S. as of March 23, 2022

CDC is continuing to get reports of HPAI H5N1 in both wild and commercial poultry and backyard flocks. Twenty-five states have detected the virus in wild birds and there have been 54 outbreaks in 17 states in commercial poultry/backyard flocks.

There have not been any human cases documented at this time and the threat to the general public is low. Risk to poultry workers, outbreak responders and waterfowl hunters may be increased as wild bird and poultry outbreaks continue, which may lead to a human case in the U.S. It is safe to eat properly handled and cooked poultry.

For more information:



There has been an increase in flu activity in the southern hemisphere in the early fall. Where is the virus coming from?

Alicia Budd

I haven’t heard of anything specific. As long as the viruses are circulating somewhere in the world, they can get a foothold anywhere. We are seeing other respiratory viruses like RSV outside of their typical timeframe, as well.



The 2022 Influenza Vaccine meeting, What’s Up with Flu in ’22! Surveillance, Vaccines, Policy, and Communications Last Year and Next, will be held virtually on May 19, 2022, from 2:00–4:45 p.m. (ET). Pre-meeting registration is required by 5:00 p.m. (PT)/8:00 p.m. (ET) on May 18, 2022, to attend. For more information and to register, visit: https://www.izsummitpartners.org/2022-naiis/.


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