Since the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines in the United States in 1987, invasive outbreaks of Hib have become rare, but a report in Morbidity and Mortality Weekly Report published today describes two recent clusters among homeless adults who would not have been eligible for vaccination.

The two clusters of cases were genetically distinct and sickened 44 individuals from 2023 through 2025. One cluster occurred in Alaska (14 cases), and a second occurred in Washington (23) and Oregon (7).

88% not eligible for routine vaccination

Overall, 40 (91%) of the 44 patients did not have documentation of receipt of Hib vaccination, and 35 (88%) would not have been eligible for routine vaccination as children because they would have been older than the recommended age range in 1987. The average patient age was 53.5 years.

Sixty-eight percent of the patients were homeless at the time of infection, and 77% said the used illicit substances. Forty-three (98%) patients had bacteremia and 42 (95%) had pneumonia.

“These emerging Hib clusters reveal that adults, particularly those using substances or experiencing homelessness or housing instability, are at risk for this otherwise rare vaccine-preventable disease,” the authors said.

Only some post-acute conditions often attributed to long COVID truly occur more often after SARS-CoV-2 infection than after other viral respiratory diseases, according to a non–peer-reviewed meta-analysis published this week on the preprint server medRxiv.

From June 2024 to April 2025, an international roster of researchers conducted a systematic review and meta-analysis of 14 multicenter cohort studies comparing 24 lingering conditions or symptoms in adults after SARS-CoV-2 infection with those occurring after other acute respiratory viral infections.

Heart rate abnormalities of borderline significance

The included studies were conducted in North America, Asia, Europe, or on multiple continents, and comparator groups most often involved influenza-like illness (ILI), influenza, and respiratory syncytial virus (RSV) in both hospitalized and non-hospitalized patients.

Distinguishing pathogen-specific sequelae from common post-viral syndromes has important implications for patient counselling, risk stratification, health-care planning, and the design of post-infectious surveillance and rehabilitation strategies.

Increased post-COVID risk was noted for pulmonary embolism (relative risk [RR], 1.77), abnormal breathing (RR, 1.59), fatigue or malaise (RR, 1.39), hemorrhagic stroke (RR, 1.23), memory loss/brain fog (RR, 1.34), and palpitations (RR, 1.23); heart rate abnormalities were of borderline significance (RR, 1.24). Pooled estimates of most other outcomes were inconclusive.

No increased risk was seen for anxiety or depression, acute coronary syndrome, cerebrovascular disorders, headache, loss of smell or taste, or sleep problems, which the authors said suggests substantial overlap between long COVID symptom and conditions and those occurring after other respiratory virus infections.

“These findings suggest that post-acute infection syndromes may occur after non-COVID respiratory infections and share many clinical features with post-COVID condition (PCC), whereas SARS-CoV-2 infection may increase the risk of specific thrombotic, autonomic, and neurocognitive outcomes,” the researchers concluded.

“Distinguishing pathogen-specific sequelae from common post-viral syndromes has important implications for patient counselling, risk stratification, health-care planning, and the design of post-infectious surveillance and rehabilitation strategies,” they added.

The study’s limitations were inclusion of mostly retrospective studies, limiting causal inference and introducing potential misclassification and residual confounding, especially for subjective symptoms evaluated long after infection. Also, the lack of stratified data by viral variant, vaccination status, timing of post-acute outcome, and clinical setting limited the findings’ generalizability, the authors noted.

Survivors of Lassa fever may experience a range of post-infection complications, including hearing loss, according to a meta-analysis published in the Journal of Infection. 

For the analysis, researchers at Imperial College London analyzed data from six studies on post-acute sequelae (lingering health effects in the weeks and months after initial infection) among 559 people who had recovered from Lassa fever, a viral hemorrhagic illness endemic to parts of West Africa. 

They found that Lassa fever survivors reported an array of post-infection complications, including musculoskeletal, cardiovascular, ocular, and psychiatric symptoms. The most common post-infection complaint was hearing loss, with a pooled prevalence of 18%. 

Severity of hearing loss varied widely

Across five of the six studies included in the review, roughly half of survivors who had hearing loss developed it in both ears (though the exact percentage varied quite a bit between the studies). In 42 survivors across four of the studies, the severity of hearing loss varied widely, with most experiencing mild to moderate hearing loss and a minority experiencing complete deafness. 

Only one of the six studies examined risk factors for post-infection hearing loss. The findings showed no meaningful differences in terms of age, sex, or treatment with antiviral therapy between those who did and did not develop hearing loss. 

Survivors reported several other symptoms related to the audiovestibular system, including tinnitus (ringing in the ears), balance disorders, vertigo, and lightheadedness. 

While some hearing loss is likely to be permanent, note the researchers, the combined evidence suggests that Lassa fever–related hearing loss improves over time in most patients and that some patients may recover completely. 

Yet, given the prevalence of auditory symptoms, the researchers write, “screening and treatment programmes for hearing loss after hospital discharge would benefit Lassa fever survivors.”

Inspection Service (APHIS) reported new detections of H5N1 avian flu, with positive tests revealing the virus in five Idaho dairy herds.

The milking cows were the first avian flu detections in cattle since a Wisconsin report in December 2025. The new detection comes almost exactly two years since US officials first recorded avian influenza in dairy cattle.

RNA detected in bull semen

In related news in Emerging Infectious Diseases, researchers examined bovine semen to determine if shedding of the virus in semen could result in silent viral spread within herds and across geographic regions through artificial insemination.

The study, published yesterday, was based on observations of natural breeding bulls on an H5N1-affected dairy farm in California, and was inconclusive in determining if semen was a good conduit for the virus, with limited evidence of seroconversion. The investigators found the RNA (genetic material) of highly pathogenic avian influenza (HPAI) H5N1 virus but not live virus in semen from a bull that was displaying no flu symptoms.

“Further research and risk assessments are needed to determine tissue tropism of HPAI H5N1 in reproductive organs and whether naturally infected bulls shed virus in semen, and, if so, evaluate the risk for disease spread on dairy farms and with artificial insemination programs,” the authors wrote.

APHIS reported 3 commercial outbreaks this week

In other avian flu news, APHIS reported outbreaks on three commercial poultry operations this week, including two in South Dakota and one in Arkansas. In Charles Mix and Edmunds counties in South Dakota, commercial turkey facilities reported outbreaks affecting 46,300 and 13,800 birds, respectively. And in Clay County, Arkansas, a large outbreak affected 191,200 birds at a commercial broiler production.

In the past 30 days, there have been 41 confirmed avian flu outbreaks including 27 commercial flocks and 14 backyard flocks, affecting 1.6 million birds.