Respiratory Diseases
Influenza-like illness
Flu season is still dragging on, but indicators are moving in the right direction. Two more states have moved out of high and very high activity levels—39 jurisdictions are now at moderate, low or minimal activity, compared to 37 last week.
Visits to the doctor for influenza-like illness (that is, fever and cough or sore throat) decreased this week to 3.7%. We are getting closer to, but are still above, the baseline of 3.1%. Once we drop below that, we will have hit the end of flu season.
Outpatient influenza-like illness held roughly steady for the youngest age groups this week, at 10.3% for those aged 0-4 and 7.4% for those aged 5-24. It decreased slightly for all other ages, with all at or below 3%.
More severe illness remains moderate, but is also declining. ED visits decreased slightly to 2.4% this week. Hospitalizations also decreased, to 2.1 hospitalizations per 100,000 people.
This flu season has been particularly rough for children. Interim assessments by the CDC categorize this season as moderate for adults and older adults, and severe for children. The cumulative hospitalization rate for children is the second highest it has been since the 2010-2011 flu season.
Flu B continues its rise, accounting for 73% of clinical lab samples and 40% of public lab samples.
COVID-19
Covid-19 activity is pretty low and continuing to decline further. The Center for Forecasting and Outbreak Analytics estimates that in most states, Covid-19 is likely declining (i.e., that the reproductive rate is <1).
ED visits held steady at a low 0.5% nationally. Covid-19 is sending slightly higher numbers of people to the ED in the South and Midwest (~0.6%) and wastewater activity in both regions is moderate. Activity remains lowest in the West, with ED visits a bit under 0.4% and very low wastewater activity. The Northeast is right in between.
Hospitalizations have been gently declining since the beginning of January, and are now down to a low 1.0 hospitalizations per 100,000 people.
RSV & Other Bugs
RSV: RSV was very slow to ramp up this year, which means we are seeing peak season quite a bit later than we usually do. We are just now reaching the levels of activity we typically see in late December/early January.
However, it does appear that we may have peaked. Test positivity dipped slightly this week to 8.6%. While ED visits held roughly steady at a moderate 0.5% for the total population, rates decreased slightly for the youngest age groups. They dipped to 4.7% for those <1 year, and to 4.0% for those 1-4 years old.
Similarly, hospitalizations decreased slightly to 2.8 hospitalizations per 100,000 people. There was a steep drop in hospitalization for babies (<1 year), dropping from 39 to 27.4 hospitalizations per 100,000 this past week. Hospitalizations also decreased several points for those 1-4 years of age, decreasing to 11.6.
Other Bugs: Cold season is not over either.
- Human coronaviruses remain very high.
- Human metapneumovirus continues its upward climb, though the rate is slowing, suggesting we are nearing peak.
- Adenovirus is spreading at moderate-to-high levels.
- Parainfluenza and rhinoviruses/enteroviruses remain very low.
Norovirus
Norovirus continues to ratchet up, reaching a new peak for the season: 16.4% test positivity. Every region reported high or very high and rising rates this week.
Stomach bugs spread extremely easily. You can reduce your risk of becoming infected by washing your hands with soap and water regularly, avoiding touching your face, and avoiding communal food (e.g., bowls of nuts and candy).
If someone in your household becomes ill, clean hard surfaces with soap and water, or with a diluted bleach solution; use the sanitizing cycle on a dishwasher to wash dishes; and wash and dry clothes and linens at the highest possible heat setting.
Norovirus continues to spread very effectively for a few days after symptoms stop, so it is best to stay home and avoid preparing food or drinks for others for at least 2-3 days after you start to feel a bit better.
Food recalls
The following foods are being recalled because they are contaminated. Please check your cupboards and throw out any of these items:
New:
- Nothing new this week
Previously Reported:
- Expanded recall of frozen chicken fried rice products, sold under multiple brand names: Trader Joe’s, Ajinomoto, Kroger, Ling Ling, and Tai Pei, due to possible glass shards (more info)
- Great Value (sold at Walmart) Cottage Cheese (more info)
- Elite Treats Chicken Chips (for dogs). These may be contaminated with salmonella, which poses a health risk not only for dogs, but also for humans who handle the product or contaminated surfaces (more info).
- Bremer Family Size Italian Meatballs (frozen, ready-to-eat) (more info)
- Multiple flavors of cream cheese under the Made Fresh Salads, Inc. label (more info)
- Gerber Arrowroot biscuits (more info)
- Organic chia seeds sold by Navitas Organics (more info)
In other news
Regional editions are wrapping up for the season. The last state-level edition will publish March 22, with regional coverage resuming in October when flu season resumes. In the meantime, paid subscribers will continue to receive a weekly national report through the summer months, which matters more than it might sound, as Covid-19 tends to surge in summer. Free subscribers will receive occasional essays through the summer months.
How effective were the flu vaccines this year? CDC recently published an interim assessment of flu vaccine effectiveness for this season (2025-2026) in the US.
For children between 6 months and 18 years, the seasonal flu vaccine was 38-41% effective against outpatient visits and 41% effective against hospitalization. For adults, the vaccine was 22-34% effective against outpatient visits, and 30% effective against hospitalization.
This level of vaccine effectiveness is fairly average, but a bit on the lower end. This is likely because there was a bit of a mismatch between the circulating strains and the strains selected for the vaccine. When season flu vaccines are made each year, there is a bit of guesswork involved to try to select strains that will be most common the coming season. This year, the match was not great owing to the emergence and subsequent dominance of H3N2 subclade K.
FDA expands approval for RSV vaccine to include younger adults at high risk. Arexvy was previously approved for use in older adults. The FDA has now approved the use of Arexvy (produced by GSK) for adults 18-49 who are at increased risk of lower respiratory tract disease due to RSV. Examples of people at higher risk include those with heart disease, asthma, COPD, cystic fibrosis or other lung diseases, chronic heart failure, diabetes, or chronic kidney disease.
Measles spread continues. There have been 1,362 cases of confirmed measles so far this year in the US, across 31 states. I write regularly about the importance of achieving high (>95%) rates of vaccination to stop community spread and achieve herd immunity. Herd immunity protects everyone, including the most vulnerable to severe illness: infants who are too young to be vaccinated, individuals who cannot be vaccinated for medical reasons (such as an allergy), or immunocompromised individuals who have been vaccinated but do not have adequate immune protection. A recent story published by ABC News about Makayla Skjerva, a 14-year-old girl from North Dakota, highlights the risks that losing herd immunity poses to immunocompromised individuals. Despite being fully vaccinated, Makayla became severely ill after a measles exposure at her school, eventually needing intensive care and a respirator. She was so sick that doctors advised her family to say their goodbyes. Fortunately, she survived, but was hospitalized for weeks, is still recovering her ability to walk, and has not yet returned to in-person schooling.
For clinicians: FOI Clinical goes deeper on reportable diseases and sends real-time health alerts when it matters. Learn more at https://www.foiclinical.com.
