Thread by @kerpen

Friday Fluday Thread: Influenza-Like Illness Data for MMWR Week 16, ending April 24, 2021

United States Influenza testing, MMWR week 16.

CDC flu view. cdc.gov/flu/weekly/ind…

2016 to 2019 4-year average: 1,759 cases; 10.67% positive
2020: 67; 0.61%
2021: 20; 0.07%

docs.google.com/spreadsheets/d…

United States Influenza testing, season to date (30 weeks, MMWR 40 to 16)

Five-year average: 204,644 cases; 18.60% positive

This year: 2,038; 0.14%

Season-to-date U. S. flu hospitalizations down 98.9% from last year.

Flu hospitalizations total (30 weeks) in FluSurv-NET catchment is 224 (+1 from last week). Through week 16 last year (29 weeks) it was 19,932 (+87).

Rate last year: 68.3 per 100K
This year: 0.8 per 100K

Influenza-Like Illness (ILI) continues to track well lower than the mild 2015-16 and 2011-12 seasons, flat again this week.

Latest U.S. non-SARS-CoV2 syndromic data from BioFire.

Lots of rhinoviruses (rising again sharply) and some adenoviruses all year.

Flu A, B micro-wave already over. RSV, and PIV back at low levels.

syndromictrends.com/metric/panel/r…

Out-of-season HCoV surge continues after a year of absence as SARS-CoV2 recedes. HCoV-NL63 rises back up to its peak. HCoV-OC43 post peak? HCoV-229E stalls. Still almost no HCoV-HKU1, last year's dominant HCoV.

CDC data similar picture, although no sign of OC43 decline yet. cdc.gov/surveillance/n…

CDC HCoVs by regions.
cdc.gov/surveillance/n…

Florida. Schools open all year. No lockdowns since September. Rhinoviruses and some adenoviruses but still nearly no flu. But ILI rising, driven by rhino, RSV, adeno, and especially PIV, which rose again but decelerated.

RSV ED visits may have peaked.

floridahealth.gov/diseases-and-c…

Sweden week 16. No masks, no lockdowns, no school closures under age 16 -- and a full year with no Flu A, Flu B, or RSV; RSV ticks down slightly after reappearing finally two weeks ago. HCoVs tick down again, in normal range.

karolinska.se/globalassets/g…

Germany week 16. The opposite of last week. Rhinoviruses rise for second week in a row; slight decrease for HCoVs and increase for SARS-CoV2, so that inverse relationship holds.
influenza.rki.de/Wochenberichte…

Brazil. Very lax control measures, and a president who urges people to disregard them. A completely skipped flu season.
apps.who.int/flumart/Defaul…

The global flu chart from WHO.
apps.who.int/flumart/Defaul…

The exceptions.
apps.who.int/flumart/Defaul…

It wasn't masks, which were never used in many countries where flu disappeared and have also been shown to be ineffective for stopping influenza in many, many studies.

apps.who.int/iris/bitstream…

Japan masks every year, and pushed masks hard in 2019 with no apparent effect. But in 2020-21 flu disappeared with low stringency COVID intervention.
apps.who.int/flumart/Defaul…

The idea mitigations worked but unmitigated SARS-CoV2 just has a higher R (popular now among the same crowd that still said "twindemic!" when flu had been gone for months) is way too facile.

Outside of testing ramp up, I don't think we've seen R > 2, even in places without NPIs.

Rhinoviruses bounced right back despite lower R and RSV was gone until recently with comparable R to SARS-CoV2.

HCoVs were gone until SARS-CoV2 declined, then returned even with lockdown.

Plus, as Biden adviser Dr. Michael Osterholm points out, our mitigation just hasn't been very effective.

Maybe in places like Australia and New Zealand where mitigations stopped SARS-CoV2 they also stopped other viruses.

But in countries where SARS-CoV2 went wild? No.

Osterholm: "There is this viral interference"

Viral interference is a well-known (but poorly understood) phenomenon. Interference from rhinovirus is generally thought to have ended the swine flu epidemic in 2009.
thelancet.com/journals/lanmi…

This great short article from @m_soond explains the viral interference theory of this respiratory season: medium.com/illumination-c…

Overall the season has been so mild that drug store chains took big losses.

Rite Aid CEO Heyward Donigan: "During the fourth quarter our industry was impacted by a historically soft cough, cold and flu season."
forbes.com/sites/brucejap…

Pediatric internships and residencies have to be extended or supplemented because they just didn't have enough patients to gain the normal amount of clinical experience.
aappublications.org/news/2021/03/1…

CDC still reports just one pediatric flu death this season.

The numbers in chart in previous tweet are lab-confirmed only, but flu testing is limited so CDC also published best estimates of total pediatric flu deaths.
cdc.gov/flu/about/burd…

COVID testing is much, much more abundant that flu testing and the definition of deaths typically used (any cause of death within X days of a positive test result) tends to overcount.

The CDC examined 182 pediatric death certificates that included COVID in calendar year 2020 and found that 64 of them (35%) had a cause of death with no plausible connection to COVID.

https://twitter.com/andrewbostom/status/1379861668847566849

Keeping that in mind, this table compares CDC best estimates of pediatric flu deaths in recent years with the first two seasons of pediatric COVID deaths.

(Note that everywhere in the world where COVID was epidemic, it circulated *instead of*, not in addition to, influenza.)

We are now near the end of the *safest* respiratory season for children ever recorded. (Even where schools never closed and nobody masked.)

Yet many places locked children out of school, and some places are still doing so. Many more kids are masked. It's a disgrace.