It's peak flu season and Covid-19 is ticking up, too.

Dec 30, 2024

"I meant to take this week off, but after reviewing the latest respiratory disease data, I thought it was worth sending a quick note.

"Outpatient influenza-like illness rose sharply this week, reaching 4.9% from 3.8% the week prior—the largest single-week increase we've seen this season. We are in the middle of what is likely peak season, so I expect we'll see another week or two of rise and then we'll have to descend the other half of the curve.

"Young children continue to be the most affected. Outpatient illness in the 0-4 age group jumped to 13.1%, while the 5-24 age group rose to 8.1%. Older age groups remain in the 2-4% range. School-age and young children are also seeing sharp increases in emergency department visits. However, older adults have the highest risk of influenza-related hospitalization.

Emergency department visits for influenza by age group. Source: CDC

"Most of the country is now in the thick of it, with nine states reporting very high levels of ILI activity. Oregon and Louisiana are particularly heavily affected, but New York City, California, and most of the Southern region are also in the ‘very high’ category. Most of the Midwest and Northeast are in better shape, though it varies by state.

Source: CDC

"After a late start to the Covid-19 season, it’s now making a comeback. Most of the country is reporting high or very high levels of wastewater concentration of SARS-CoV-2. Test positivity, emergency department visits and hospitalizations are all also rising.

"Most of the country seems to be affected by these recent increases, though it's hard to get a clear sense of geographic trends because some of the indicators disagree about hotspots. Wastewater concentration, for example, is lower in the South, but emergency department metrics still show an increase there (see plot). I'll keep an eye on trends in the weeks ahead to get a better sense of what we can expect in the new year.

ED visits for Covid-19 (orange line) are clearly rising in the Southeastern states. Source: CDC

"Last but not least, RSV activity is elevated as expected this time of year, but we are enjoying a somewhat lighter year than normal. Hospitalizations remain well below last year’s high water mark and are leveling off.

"For now, I think ILI is the most immediate risk, though of course prevention measures (e.g., masking, ventilation) are the same for all three of these respiratory pathogens. The bottom line is there is a lot going around, so be careful out there.

"Be well, and happy New Year!

-Caitlin

"P.S. I have a brief essay in Wired on a strategy for improving outbreak response, if that is of interest. I published a longer piece on a similar topic in Foreign Affairs over the summer."