Respiratory virus activity from flu, COVID-19, and respiratory syncytial virus (RSV) continues to decline across most of the country, with only two jurisdictions—North Dakota and Wyoming—reporting high activity, the Centers for Disease Control and Prevention (CDC) said in updates today.

In its weekly FluView update, the CDC said key markers such as test positivity continue to fall, and only one region is above its regional baseline for outpatient visits for flulike illness: the northeast. All three viruses are circulating, with influenza A making up 62.4% of samples at public health labs. Of subtyped influenza A samples, about half were 2009 H1N1, and half were H3N2.

Hospitalizations continue to decline, but overall deaths were up slightly. The CDC received reports of 4 more pediatric flu deaths, raising the season's total to 142. 

COVID wastewater detections minimal, highest in the Midwest

For COVID, the CDC's latest data updates show more declines for both severity indicators (hospitalizations and deaths) and early indicators (test positivity and emergency department visits). Wastewater SARS-CoV-2 detections, another early indicator, have declined to the minimal level and are currently highest in the Midwest.

In its weekly respiratory virus snapshot, the CDC said for RSV, all 10 regions are below the 3% epidemic threshold, suggesting that the season is ending. RSV hospitalizations remain low for all age-groups.

In this week’s Morbidity and Mortality Weekly Report, researchers review COVID-19 activity and vaccination in US nursing homes from October 2023 through February 2024 and find up to 26% of nursing homes reported at least one case of COVID-19 during each week of the study period.

The study was based on information gathered as part of the Centers for Disease Control and Prevention’s (CDC) National Healthcare Safety Network.

Weekly rates of incident SARS-CoV-2 infection ranged from 61.4 per 10,000 nursing home residents during the week ending February 11, 2024, to 133.8 per 10,000 during the week ending December 3, 2023. The cumulative weekly SARS-CoV-2 infection rate was highest in the Midwest region (130.1 per 10,000 residents) and lowest in the South (93.1 per 10,000).

The same geographic pattern was seen among COVID hospitalizations: The cumulative weekly COVID-19–associated hospitalization rate was 5.8 per 10,000 residents and was highest in the Midwest (6.7 per 10,000) and lowest in the South (5.0 per 10,000), the authors said. 

CDC recommends updated vaccines to older Americans 

Nursing homes were the first epicenters of the pandemic in the United States in 2020, as those 85 years and older are the most likely to die from infections with the novel coronavirus. Despite the risk of severe infection from COVID-19, the study authors found that only 40.5% of residents were up to date with COVID vaccination by the end of the study period. Residents in the South had the lowest rate (32.4%), compared to residents in the Northeast, who had the highest (47.3%).

"This finding indicates that an important prevention tool is being underutilized in this population," the authors concluded.

This finding indicates that an important prevention tool is being underutilized in this population.

In February, the CDC recommended that all adults aged older than 65 years receive one additional dose of an updated 2023–2024 COVID-19 vaccine at least 4 months after the previous updated dose.

From 1970 to 2021, mpox cases were detected year-round in equatorial Africa but were detected seasonally in tropical regions in the Northern Hemisphere, finds an analysis of 133 zoonotic index cases led by Institut Pasteur researchers in Paris.

Published in Emerging Infectious Diseases, the study was based on peer-reviewed and "gray" (alternatively published) literature on index mpox cases of zoonotic origin in Africa over the 50-year timeframe. The team also used remotely sensed meteorologic, topographic, climate, seasonality, environmental, land use–land cover, and fire data.

"Mpox, caused by monkeypox virus (MPXV), remains a neglected tropical zoonotic disease of forested Central and West Africa," the authors wrote. "Mpox epidemiology is poorly understood, and the MPXV animal reservoir remains unknown."

Climate change could worsen seasonal drivers

Of 133 index cases from 113 sites, 64% were reported in 2000 and later, 86% were the Congo Basin/clade 1 virus, and 13% were West African/clade 2. The Democratic Republic of the Congo accounted for 44% of cases, and the Central African Republic accounted for 33%.

Determining whether specific seasons or periods bring greater risk for human transmission can improve prevention and surveillance initiatives and contribute to identifying animal reservoirs.

Cases were identified at a median latitude of 3.44°N and varied significantly by month. Most infections occurred at lower latitudes from January to July (not including April) but were seen mainly at higher latitudes from August to December. Index cases were primarily identified in equatorial cool (33%), northern cool wet-dry (35%), and northern hot wet-dry climates (17%).

The researchers noted a potential high-risk season from August to March, which spans the last 3 months of the rainy season and the entire dry season. "That finding suggests complex drivers likely related to human and wildlife ecology," they wrote. "Various seasonal activities can increase human contact with wildlife."

Climate and environmental changes could worsen seasonal drivers of human MPXV exposure, the authors said: "Determining whether specific seasons or periods bring greater risk for human transmission can improve prevention and surveillance initiatives and contribute to identifying animal reservoirs. For this, a genuine One Health approach is crucial."

• The US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) yesterday said H5N1 avian flu has been confirmed in 1 more dairy herd, which involves another from Michigan, raising the national total to 29. The virus has now been found in 5 Michigan dairy herds. In a related development, Michigan agriculture and health officials yesterday posted a statement reminding the state's residents about the risk of drinking raw (unpasteurized) milk amid the outbreak involving dairy cows. 
• The number of mpox cases in the United States so far this year is more than double the number reported at this time in 2023, the Centers for Disease Control and Prevention (CDC) said, based on data collected as of April 13. So far, 750 cases have been reported in 2024, up sharply from 336 reported during the same time last year. Hot spots include the Middle Atlantic and South Atlantic regions, including New York City and the District of Columbia.
• Three African countries reported more polio cases this week, all involving vaccine-derived strains, the Global Polio Eradication Initiative (GPEI) said in its latest weekly update. The Democratic Republic of the Congo (DRC) reported an infection involving circulating vaccine-derived poliovirus type 1 (cVDPV1) in a patient from Haut Katanga province, its first of the year involving the strain. Chad reported a circulating vaccine-derived poliovirus type 2 (cVDPV2) case from Mandoul, its first of the year. Also, Nigeria reported one more cVDPB2 case, with affected a patient from Kebbi, raising its total for the year to eight.