#14,460
Despite a plethora of cautionary media reports predicting very bad flu season ahead - in truth - no one really knows what this winter will bring. That said, we've seen several consecutive years of moderately severe to severe flu, and there are some warning signs that might indicate another rough season ahead.
The most obvious is that the WHO recently switched out two of the four vaccine components for next year's Southern Hemisphere flu vaccine (see WHO Announces 2 Strain Changes For 2020 Southern Hemisphere Flu Vaccine), raising concerns over how good of a match this fall's vaccine will be for A/H3N2 and B/Victoria strains.The biggest wild card remains A/H3N2, which continues to evolve and diversify (see The Enigmatic, Problematic H3N2 Influenza Virus), having persisted in the human population now for over a half of century.
Another concern is the later-than-usual arrival of flu vaccines for much of the Northern Hemisphere, due to manufacturing problems. Canada, the UK, and Taiwan have all announced delayed vaccination campaigns this fall.
Much has also been made about Australia's heavy and prolonged 2019 flu season, but what happens over our summer in Australia isn't necessarily a harbinger of what happens the following winter in North America.All of which brings us to yesterday's MMWR report on flu activity in the United States over the summer, and a look at the 2019-2020 flu vaccine.
The big surprise is the surge in A/H3N2 clade 3C.3a which came to dominate late last winter, appears - at least among the small sample of viruses gathered over the summer - to have reversed itself (see chart at top of blog).
Whether that trend continues once influenza activity picks up again remains to be seen. Clade 3C.3a was barely on our radar at the start of last year's flu season, but soared to prominence in January and February, which illustrates how quickly things can change in the flu world.Despite a high degree of uncertainty over the upcoming flu season and a feared mismatch with the flu vaccine, the overriding message in this MMWR report is the seasonal flu vaccine remains the best protection we have against influenza infection.
I've already gotten my shot, and hopefully I'm building immunity to the strains that will be visiting my neighborhood in the months ahead.But even if an antigenically different strain appears, I'll derive a bit of comfort from evidence that suggests getting the flu vaccine may help reduce the severity of one's illness, even when it doesn't prevent infection (see CMAJ Research: Repeated Flu Vaccinations Reduce Severity of Illness In Elderly).
I've only reproduced some excerpts from a much longer MMWR Report, so follow the link to read it in its entirety.
Update: Influenza Activity — United States and Worldwide, May 19–September 28, 2019, and Composition of the 2020 Southern Hemisphere Influenza Vaccine
Weekly / October 11, 2019 / 68(40);880–884
Scott Epperson, DVM1; C. Todd Davis, PhD1; Lynnette Brammer, MPH1; Anwar Isa Abd Elal1; Noreen Ajayi, MPH1; John Barnes, PhD1; Alicia P. Budd, MPH1; Erin Burns, MA1; Peter Daly, MPH1; Vivien G. Dugan, PhD1; Alicia M. Fry, MD1; Yunho Jang, PhD1; Sara Jo Johnson, MPH1; Krista Kniss, MPH1; Rebecca Kondor, PhD1; Lisa A. Grohskopf, MD1; Larisa Gubareva, PhD1; Angiezel Merced-Morales, MPH1; Wendy Sessions, MPH1; James Stevens, PhD1; David E. Wentworth, PhD1; Xiyan Xu, MD1; Daniel Jernigan, MD1
SummaryDuring May 19–September 28, 2019,* low levels of influenza activity were reported in the United States, with cocirculation of influenza A and influenza B viruses. In the Southern Hemisphere seasonal influenza viruses circulated widely, with influenza A(H3) predominating in many regions; however, influenza A(H1N1)pdm09 and influenza B viruses were predominant in some countries.
What is already known about this topic?
Although influenza activity is typically low in the United States during the summer months, CDC collects, compiles, and analyzes data to monitor influenza activity throughout the year.
What is added by this report?
In the United States, influenza activity remained low with cocirculation of influenza A and influenza B viruses. Influenza viruses circulated widely in the Southern Hemisphere, with A(H3) viruses predominating in most regions, although influenza A(H1N1)pdm09 and influenza B/Victoria viruses predominated in several countries.
What are the implications for public health practice?
Receiving a seasonal influenza vaccine each year remains the best way to protect against seasonal influenza and its potentially severe consequences.
In late September, the World Health Organization (WHO) recommended components for the 2020 Southern Hemisphere influenza vaccine and included an update to the A(H3N2) and B/Victoria-lineage components. Annual influenza vaccination is the best means for preventing influenza illness and its complications, and vaccination before influenza activity increases is optimal. Health care providers should recommend vaccination for all persons aged ≥6 months who do not have contraindications to vaccination (1).(SNIP)
Discussion
From May to September 2019, influenza activity remained low in the United States, as is typical for that time of year. Influenza A and B viruses cocirculated throughout the summer months with influenza A(H3N2) viruses predominating overall and influenza B/Victoria, subclade V1A-3Del, viruses the most common influenza B virus reported by public health laboratories. Influenza A and B viruses also circulated widely in the Southern Hemisphere with the predominant virus varying by region and country.
It is too early in the season to know which viruses will circulate in the United States later this fall and winter or how severe the season might be; however, regardless of what is circulating, the best protection against influenza is an influenza vaccination. Influenza vaccination has been shown to reduce the risk for influenza illness associated with outpatient health care visits and hospitalizations and reduces the risk for serious influenza outcomes that can result in hospitalization or death.
CDC recommends that all persons aged 6 months and older who do not have contraindications get vaccinated, but vaccination is especially important for persons at high risk for serious influenza-associated complications, including persons aged ≥ 65 years, children aged < 5 years, pregnant women, and persons with certain underlying medical conditions.
In late September, WHO issued its recommendations for the 2020 Southern Hemisphere influenza vaccine. Compared with the composition of the 2019–20 Northern Hemisphere influenza vaccine formulation, these recommendations reflect changes to the A(H3N2) and B/Victoria-lineage components.
The update for the B/Victoria-lineage component reflects the global spread and increase of V1A-3Del viruses, which had reduced reactivity to ferret antisera raised to V1A.1 viruses used in 2019–20 Northern Hemisphere vaccines. Apart from North and South America, the majority of A(H3N2) viruses circulating elsewhere globally belonged to subclade 3C.2a1 and were antigenically different from the Northern Hemisphere 3C.3a vaccine component, leading to a change in the A(H3N2) component to a 3C.2a1 subclade virus for the Southern Hemisphere.
These recommendations were made specifically for the Southern Hemisphere using many factors, including evolutionary approaches to forecast specific subgroups likely to circulate 6 months into the future, determining which candidate vaccine viruses induce immunity that blocks the largest variety of viruses and which viruses escape population immunity from prior infection or vaccination. These factors vary among countries within the Southern Hemisphere and certainly vary between the Southern and Northern Hemispheres. For example, activity in Australia during recent seasons has not reflected influenza virus activity in the subsequent U.S. season.
Changes to the Southern Hemisphere vaccine composition, therefore, might not be a good predictor of the upcoming U.S. influenza season. Although Australia experienced an early start to its 2019 season with influenza A(H1N1)pdm09 viruses circulating initially and A(H3N2) virus eventually predominating (2), influenza is unpredictable, and circumstances can change very quickly. Analysis of surveillance and laboratory data to date continues to support the appropriateness of the Northern Hemisphere vaccine viruses used in production of influenza vaccines for the upcoming U.S. season.
Except for one influenza A(H1N1)pdm09 virus and one influenza B virus, all influenza viruses tested remained susceptible to oseltamivir, peramivir, and zanamivir, and only one virus contained a genetic mutation that has previously been associated with reduced susceptibility to baloxavir. Influenza antiviral medications are a valuable adjunct to annual influenza vaccination, and early treatment with influenza antiviral medication, especially within 48 hours of symptom onset, is recommended for patients with confirmed or suspected influenza who 1) have severe, complicated, or progressive illness; 2) require hospitalization; or 3) are at high risk for influenza-related complications§§ (3). Early treatment has been shown to decrease time to symptom improvement (4–7) and to reduce secondary complications associated with influenza (8,9).
Health care providers should not delay treatment until test results become available because treatment is most effective when given early in the illness. Additional information regarding influenza viruses, influenza surveillance, influenza vaccines, influenza antiviral medications, and novel influenza A virus infections in humans is available at https://www.cdc.gov/flu.(Continue . . . )
