#16,645
After an early start, and peaking in late December, this year's flu activity declined rapidly after the New Year and seemed on its way out until about six weeks ago, when we began to see a leveling off and then a slow rise in cases, particularly in the middle of the nation.
While not a huge resurgence, the disruptions of flu's normal routine by the pandemic makes influenza even more unpredictable than usual, and late season - and even out-of-season summer outbreaks - are possible (see MJA: Preparing For Out-of-Season Influenza Epidemics When International Travel Resumes).
First, the key points from this week's FluView Report, followed by a statement by the CDC on rising flu cases which makes the case for getting the flu vaccine (if you haven't) despite a poor interim Vaccine Effectiveness (VE) estimate published a week ago in the MMWR.
I'll return with a brief postscript after the break.
Key Points
- Influenza activity is increasing in most of the country.
- The highest levels of influenza percent positivity from clinical labs were seen in states in the central and south-central 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 increased slightly this week but is still 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 six weeks.
- The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, 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 13 pediatric deaths reported this season.
- CDC estimates that, so far this season, there have been at least 2.9 million flu illnesses, 28,000 hospitalizations, and 1,700 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.
- Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
- There are also flu antiviral drugs that can be used to treat flu illness.
Flu Activity Increasing Late in the Season
Vaccination now could still be beneficial per CDC
March 18, 2022—CDC’s most recent FluView report shows that flu activity is increasing across most of the United States after declining from mid-December through January. Currently, activity is highest and increasing fastest in the central and south-central parts of the country. This is an unusual time for flu activity to be increasing, and it is unclear how long increases will continue. Flu activity is hard to predict, and CDC believes that flu vaccination at this time could still be beneficial for people who have not yet been vaccinated. While preliminary vaccine effectiveness estimates suggest that this season’s vaccines have not reduced the risk of mild to moderate illness caused by the most common H3N2 viruses, vaccination has been shown in the past to offer protection against more serious outcomes in people who get vaccinated but still get sick. Vaccination also could protect against illness caused by other flu viruses if those begin to circulate more commonly later this season.
According to CDC’s surveillance systems, the proportion of respiratory specimens testing positive for flu in clinical laboratories nationally has increased for six weeks. Nationally almost 7 percent of respiratory specimens tested at clinical labs were positive for flu during the week ending March 12, 2022, but this proportion varied across the country with highest proportions occurring in the central and south-central parts of the country and the lowest proportions occurring in the Pacific northwest and southeast. Additionally, the number of flu-related hospital admissions reported nationally to HHS-Protect increased for the sixth week in a row. More than 2,000 people were hospitalized with flu nationally during the week ending March 12, 2022. This week CDC also reported an additional three flu-related pediatric deaths, bringing the total this season to 13.
CDC continues to recommend flu vaccination as long as flu viruses are circulating and even when protection against one virus is reduced. Flu vaccines protect against four different flu viruses and vaccination could still prevent serious outcomes in people who are vaccinated but still get sick. While preliminary vaccine effectiveness estimates suggest that this season’s vaccine did not reduce the risk of getting sick and needing outpatient medical care from H3N2 flu, there is a growing body of evidence suggesting that flu vaccination attenuates severe illness, even when the circulating viruses have antigenic differences from the vaccine virus. The evidence is particularly strong in young children who are at increased risk for severe complications from flu. A study during the 2019-2020 flu season showed that during a season when there were antigenic differences between the vaccine and circulating viruses, vaccination was associated with a reduced risk of critical and life-threatening flu illness in children. The results of studies looking at how well this season’s flu vaccines are working at preventing serious outcomes this season are still to come.
Given the reduced vaccine effectiveness against the most common flu viruses causing infection now and the later than usual increases in circulation of flu, antiviral drugs for treatment are even more important. Clinicians should promptly treat people who have flu or suspected flu who are at higher risk of serious flu complications. While flu vaccination is the first and best way to prevent flu, antiviral drugs are a second line of defense that can be used to treat flu. When used for treatment, antiviral drugs can lessen symptoms and shorten the time you are sick by 1 or 2 days. They also can prevent serious flu complications, like pneumonia. For people at higher risk of serious flu complications, treatment with antiviral drugs can mean the difference between milder or more serious illness possibly resulting in a hospital stay.
In addition to vaccination and the appropriate use of flu antiviral medications, CDC recommends everyday preventive actions to reduce the spread of respiratory illness like flu. These everyday preventive actions include staying home when sick, covering coughs and sneezes, and washing your hands often.
The spread of seasonal respiratory illnesses, such as influenza, RSV, Rhinovirus, Measles, Enteroviruses (EV71, EV-D68, ect.), scarlet fever, etc. has been disrupted for the past two years by the SARS-CoV-2 virus, and our efforts to prevent its spread.
As a result, our collective immunity to these diseases is believed to be lower than normal, leaving us open to possibly seeing unusual, or out-of-season, outbreaks in the months ahead.
Last summer, the United States and many other countries saw large, and unseasonable, RSV outbreaks once face mask requirements were loosened (see CDC HAN: Increased RSV Reports Across The Southern United States). This past week, there have been reports of increased scarlet fever outbreaks in the UK for the first time in more than two years.
How all of this plays out this summer and fall is unpredictable, but we should be prepared for some surprises along the way.
