Though US flu activity continues to increase slightly in children, overall levels remain low nationally, as do COVID markers, the Centers for Disease Control and Prevention (CDC) said today in its respiratory disease updates.

Percent positivity for flu has trended upward over the past few weeks but is still low, at 1.6% at clinical labs, where nearly 93% of detections are influenza A. Meanwhile, emergency department visits for flu increased slightly among children and adolescents. 

No new pediatric flu deaths were reported, keeping the season's total at one. One death was reported for the 2023-24 season, which occurred in a child who died in May, bringing the number for last season to 205. 

COVID activity continues to decline in most areas, the CDC said in its weekly respiratory virus snapshot. 

"Across the nation, COVID-19 infections are predicted to decline in some states, and grow slowly from a low level in others," the agency said. Wastewater detections are still at the low level and are highest in the Midwest. WastewaterSCAN, a national wastewater monitoring system based at Stanford University in partnership with Emory University, said yesterday that SARS-CoV-2 detections remain low, with no significant trend up or down over the past 3 weeks.

RSV picks up more steam; more Mycoplasma and pertussis

In other respiratory illness tracking, the CDC said respiratory syncytial virus (RSV) activity is elevated and continues to increase in the East and South and is trending upward in the Central region, especially in young children. Also, infections caused by Mycoplasma pneumoniae ("walking pneumonia") continue to rise in the younger age-groups.

For pertussis (whooping cough), the CDC recently reported that illness patterns have returned to pre–COVID-19-pandemic levels. For the week ending November 9, preliminary data show that more than five times as many cases have been reported this year than last year. 

Three countries reported more polio cases this week: Pakistan had three more wild poliovirus type 1 (WPV1) cases, Nigeria noted seven more circulating vaccine-derived poliovirus type 2 (cVDPV2) cases, and Chad confirmed two cVDPV2 cases, the Global Polio Eradication Initiative (GPEI) said in its latest weekly update.

Pakistan is one of two countries where WPV1 is still endemic. The country's latest patients all had paralysis onsets in October. They are from three different provinces, Sindh, Balochistan, and Khyber Pakhtunkhwa. The cases, part of a sharp rise in cases this year, boost Pakistan's 2024 total to 48.

In Africa, Nigeria’s cVDPV2 patients had paralysis onsets in September and hail from five different states: Katsina, Jigawa, Yobe, Sokoto, and Kogi. The illnesses put the country's total for 2024 at 80. Chad's 2 cases are in Wadi Fira and Chari Baguirmi regions, also with onset of paralysis in September. They bring Chad's total cVDPV2 cases this year to 15.

Repatriation among factors fueling polio rises in endemic countries

Pakistan's forced repatriation of roughly 730,000 undocumented Afghani residents back to their home country is a factor behind setbacks in polio eradication in Pakistan and Afghanistan, Hamid Jafari, MD, who directs polio eradication activities for the World Health Organization Eastern Mediterranean regional office, said this week at a virtual meeting hosted by the GPEI, according to Voice of America. He said the virus moved with massive unpredictable population movements across borders and within the countries. 

Other factors include polio vaccination barriers in militant areas, vaccine hesitancy, and community boycotts. The report said antigovernment militants have violently attacked polio vaccination teams over suspicions of spying.  

The preventive monoclonal antibody nirsevimab (Beyfortus) was 89% effective against infant hospitalization in Alaska for respiratory syncytial virus (RSV) in their first RSV season and 76% and 88% effective against medically attended illness for those in their first and second seasons, respectively, estimates a study published yesterday in Morbidity and Mortality Weekly Report.

Researchers from the US Centers for Disease Control and Prevention (CDC) and their partners in Alaska analyzed rates of hospitalization and the receipt of outpatient or hospital care among 472 infants younger than 20 months treated for respiratory virus infection in Alaska's Yukon-Kuskokwim Delta region, located on the state's west coast, in the 2023-24 respiratory virus season.

"Historically, American Indian and Alaska Native (AI/AN) children have experienced high rates of RSV-associated hospitalization, with threefold to sevenfold higher rates in Alaska's Yukon-Kuskokwim Delta region than in other U.S. areas," the study authors wrote.

88% effective against need for treatment in second season

Of the 472 children with medically attended visits (14% hospitalization, 70% emergency department, and 16% outpatient clinic), 14% tested positive for RSV, and 86% tested negative. The median time from nirsevimab receipt to a medical visit was 91 days. In total, 48% overall had received nirsevimab at least 7 days before their medical visit (median, 91 days). 

Historically, American Indian and Alaska Native (AI/AN) children have experienced high rates of RSV-associated hospitalization, with threefold to sevenfold higher rates in Alaska's Yukon-Kuskokwim Delta region than in other U.S. areas.

Among the 292 children in their first RSV season, nirsevimab was 76% effective (95% confidence interval [CI], 42% to 90%) against medically attended RSV and 89% effective (95% CI, 32% to 98%) against hospitalization. 

Estimated nirsevimab effectiveness against RSV requiring medical care among the 180 children in their second RSV season was 88% (95% CI, 48% to 97%). Effectiveness was 90% at 7 days to 3 months and 77% 3 to 6 months post-receipt, but the authors noted wide and overlapping confidence intervals.

"These findings support current CDC recommendations for all infants in their first RSV season to either receive nirsevimab or be protected through maternal vaccination and for children entering their second season with increased risk for severe RSV illness, including all AI/AN children, to receive nirsevimab," the researchers concluded.