In its regular weekly snapshot on respiratory virus activity, the Centers for Disease Control and Prevention (CDC) said that illness levels remain high, mainly due to impacts from the flu season.

For flu, emergency department (ED) visits are very high, and test positivity—after leveling out a bit after the holidays—rose to 25% for the week ending January 18. The CDC added that ED visits for flu are rising in all age-groups. ED visits trended slightly downward after the holidays but have now started to rise again.

Wastewater tracking shows that influenza A levels are still high.

Hospitalizations for flu have also resumed an upward trend and are highest in older adults. Deaths from flu are also on the rise, making up 1.5% of all deaths for the latest reported week, which ended January 11.

COVID, RSV markers show more declines

Meanwhile, COVID-19 markers declined or remained stable. ED visits for COVID are at low levels but are highest among young children and older adults. Though wastewater detections are at the moderate level and declining in all regions, levels remain highest in the Midwest.

The CDC said its predictions for the next 2 weeks suggest that COVID ED visits will remain at a lower level compared to previous winter seasons. Test positivity for COVID remained stable, at 6.2%. 

Hospitalization rates for COVID increased, especially among seniors.

One COVID marker that rose was deaths, which were at 1.8% of all deaths for the week ending January 11, up from 1.4% the previous week.

For respiratory syncytial virus (RSV), ED visits were highest in young children, and wastewater detections are at the moderate level, with test positivity stable, at 8.8%. The CDC added that hospitalization rates for RSV—highest in young children and older people—have peaked but remain elevated.

A small trial of a hepatitis E vaccine developed in China showed that immunization was an effective strategy for curbing an outbreak at a refugee camp in South Sudan in 2022, an international research team reported recently in The Lancet Infectious Diseases.

The Hecolin vaccine was developed in China and was licensed in some countries in 2011 and is typically given as three doses. The World Health Organization (WHO) in 2015 recommended its use in outbreak settings.

Senior study author Andrew Azman, PhD, an epidemiologist at the University of Geneva/Geneva University Hospitals (UNIGE-HUG) Centre for Emerging Viral Diseases, said in a press release from the school that hepatitis E leads to about 50,000 deaths each year and that the displaced persons camp where the trial was conducted regularly experienced outbreak from the virus, likely due to poor sanitation and frequent flooding, which contribute to the spread of multiple waterborne diseases.

First use in an outbreak outside China

Until the trial, the Hecolin vaccine hadn't been used outside of China. The vaccine trial targeted people ages 16 and older. The case-control study included 859 people with suspected hepatitis E infections, of whom 201 met trial eligibility criteria. Twenty-one had lab confirmed hepatitis E infections. Of those, 10 (48%) were unvaccinated, compared with 33 (27%) of 121 matched controls. The unadjusted two-dose vaccine effectiveness was 67.8% (95% confidence interval, 28.6% to 91.9%). After adjusting for confounders, vaccine effectiveness was 84.0%, but with a wide confidence interval (95% CI, –208.5 to 99.2).

The team concluded that the findings show moderate to high effectiveness of two doses, depending on the study design and analytical method. However, they said the trial's small sample size adds an element of uncertainty.

"This evidence supports the potential for a two-dose regimen to provide substantial protection in outbreak settings, which is crucial given the logistical challenges of administering a three-dose schedule during an outbreak," they wrote.

Two countries reported new polio cases this week: Pakistan, with 3 more wild poliovirus type 1 cases (WPV1), and the Democratic Republic of Congo (DRC) with a vaccine-derived case, according to the latest weekly report from the Global Polio Eradication Initiative (GPEI).

Pakistan's 3 new cases of wild poliovirus type 1 (WPV1) occurred in December, thus raising the nation's 2024 total to 73 polio cases.

In the DRC, one circulative vaccine-derived poliovirus type 1 was reported, but no other details were provided. 

Report on recent wastewater detections in Europe

In other polio news, yesterday European researchers published a report in Eurosurveillance detailing the detection circulating vaccine-derived poliovirus type 2 (cVDPV2) in wastewater samples in Finland, Germany, Poland, Spain, and the United Kingdom. 

All detections were made in the second half of 2024. The United Kingdom had the most detections, with 12, followed by Poland (8), Germany (7), Finland (5), and Spain (2). Detection dates ranged from September 16 through November 18.

The authors said genomic analysis shows high sequence identity between isolates from different countries, suggesting genetically related cVDPV2 strains.

This observed genetic diversity argues for nearly simultaneous importations of genetically related viruses.

"This observed genetic diversity argues for nearly simultaneous importations of genetically related viruses having occurred into different European locations from an unknown country or area during a short period of time although other explanations are possible, such as some transmission occurring between European countries," they wrote.