U.S. & Canada Both Reporting Increasing Flu Activity

Credit CDC FluView Week 15

#16,708

Normally, by the last half of April we are well beyond our winter flu season, and either talking about the upcoming influenza season in the Southern Hemisphere, or waiting for flu's return in the fall.   

This spring, however, we continue to see influenza not only stubbornly hanging on, but slowly increasing, across North America and parts of Europe. 

After two years of COVID mitigation (face masks, social distancing, etc.) community levels of influenza immunity are expected to be low, and with more and more people eschewing face masks, and more social intermingling, the potential for seeing `out-of-season' respiratory outbreaks is higher than usual.  

Yesterday Canada published their FluWatch report: March 13, 2022 to April 16, 2022 (weeks 11-15) where they report a `sharp' rebound in influenza as well.

We get a similar report from this week's CDC FluView (week 15), which has noted a small, but steady, increase in flu activity for the past 9 weeks. 

Key Points

• Influenza activity varies by region. Activity is highest in the northeast, south-central and mountain regions of the country.
• The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
• The percentage of outpatient visits due to respiratory illness has steadily increased since mid-February but remains below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
• The number of hospital admissions reported to HHS Protect has increased each week for the past 11 weeks.
• The cumulative hospitalization rate in the FluSurv-NET system is higher than the end-of-seasons rates for the 2020-2021 and 2011-2012 seasons, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
• Three influenza-associated pediatric deaths were reported this week. There have been 22 pediatric deaths reported this season.
• CDC estimates that, so far this season, there have been at least 4.7 million flu illnesses, 47,000 hospitalizations, and 2,800 deaths from flu.
• An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
• There are also prescription flu antiviral drugs that can be used to treat flu illness.

While influenza activity remains well below what we would expect during the regular flu season, it is at sufficiently high enough levels that this week the World Health Organization warned:

▪ Globally, influenza activity remained low, but activity has increased since February 2022 after an initial decrease in January 2022. 

▪ With the increasing detections of influenza during COVID-19 pandemic, countries are recommended to prepare for the co-circulation of influenza and SARS-CoV-2 viruses. They are encouraged to enhance integrated surveillance to monitor influenza and SARS-CoV-2 at the same time, and step-up their influenza vaccination campaign to prevent severe disease and hospitalizations associated with influenza. Clinicians should consider influenza in differential diagnosis, especially for high-risk groups for influenza, and test and treat according to national guidance.

After two years of masking and social distancing, our immunity to a lot of viruses has likely waned. As people ditch masks, begin to travel, and mingle more, we may see scattered outbreaks of RSV, Adenovirus, or Enteroviruses (including EV-D68) over the summer. 

In late March, in The Lancet: SARS-CoV-2 Co-infection With Influenza Viruses, RSV, or Adenoviruses we saw evidence that coinfection among hospitalized patients is linked to a four-fold increased risk of requiring mechanical ventilation, and a roughly doubled risk for death.

All of which makes even a small uptick in non-COVID respiratory viruses worthy of our attention.