The World Health Organization (WHO) today reduced the number of reported hantavirus cases from the Dutch cruise ship MV Hondius from 11 to 10. 

WHO officials said at a press briefing this morning that the 11 cases reported in a disease outbreak update on May 13 included one inconclusive test in a passenger from the United States. But the agency learned yesterday that the patient has tested negative. Eight cases have been confirmed, and two are probable.

WHO Director-General Tedros Adhanom Ghebreyesus, PhD, also said that more than 120 passengers who disembarked from the ship in Tenerife are being monitored by public health officials, either in their home countries or while in transit. Twenty-seven crew members remain on board the ship and are expected to arrive in the Netherlands on Monday.

Tedros said that, because of the long incubation period for hantavirus (up to six weeks), more cases may be reported in the coming days. “This does not mean the outbreak is expanding. It shows that the control measures are working, that laboratory testing is ongoing, and that people are being cared for with support from their governments,” he said.

41 Americans being monitored

In a separate press briefing, officials from the US Centers for Disease Control and Prevention (CDC) reiterated that none of the 41 Americans under monitoring, including the 18 passengers who are being quarantined in biocontainment units at the National Quarantine Unit in Omaha, Nebraska, and Emory University Hospital in Atlanta, have tested positive for the Andes strain of hantavirus.

Others under monitoring include passengers who left the ship before the outbreak and those who may have been exposed on flights with a symptomatic passenger.

“CDC has assessed each affected US resident based on their presence on the MV Hondius during the time when Andes virus was spreading on board, or where they were seated on a plane in relation to an infected person,” said David Fitter, MD, the CDC’s incident manager for hantavirus. “Across all these groups, our focus is to ensure appropriate health monitoring and quick self-isolation and access to care if they get sick.”

Many studies show that COVID-19 vaccination reduces the risk of severe disease, hospitalization, and death. There is less evidence about whether COVID-19 shots make people less contagious.

New research, however, has found that COVID-19 patients who were vaccinated against the virus were much less likely to infect household members than unvaccinated patients, according to a study published today in JAMA Network Open.

Researchers studied 362 patients who saw a healthcare professional outside the hospital because of COVID-19 symptoms and who also tested positive for the SARS-CoV-2 virus. The study authors also followed up with about 760 of patients’ household contacts. 

Overall, 62% of household contacts of patients with the virus soon tested positive for COVID-19.

But the household contacts of patients vaccinated in the past six months were 43% less likely to test positive than household contacts of unvaccinated sick people, the study shows.

Although the vaccinated patients in the study still developed COVID-19, it’s likely that the vaccine helped them by reducing the amount of virus in their bodies, said Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, who was not involved with the new study. People with lower viral levels cough shed fewer viruses when they cough or sneeze, making them less likely to infect those around them.

Protection against transmission wanes

Household contacts were no more or less likely to test positive for COVID-19, however, if the sick person in their home was vaccinated seven or more months prior. That finding suggests that COVID-19 vaccine protection wanes over time.

The study was conducted in New York, Tennessee, and Washington state from January 1, 2024, to January 31, 2025. Patients who tested positive for COVID-19 were enrolled in the study within six days of becoming ill. Patients were excluded from the study if they were vaccinated within two weeks or less of becoming sick.

The median age of patients in the study was 35 years old.

The authors note, “While the individual benefit of COVID-19 vaccination may vary by age and chronic medical conditions, COVID-19 vaccination may have indirect benefits by decreasing transmission and thus reducing overall exposure to SARS-COV-2.”

While most respondents to a survey of US backyard flock owners had heard of avian influenza, about one third didn’t know the signs or symptoms of infection in birds or people, highlighting the need for risk messaging and educational resources.

The online survey was conducted by the Centers for Disease Control and Prevention (CDC) in collaboration with state and agricultural officials from July to December 2025. The aim was to learn more about flock owners and their knowledge, attitudes, and practices surrounding the H5 strain of avian flu that has affected millions of US poultry. Of 638 respondents, about half had an advanced degree.

Since 2024, three avian flu cases have been confirmed in people in the United States who own backyard birds, the authors noted. 

The findings were published yesterday in Morbidity and Mortality Weekly Report.

58% said someone in their home is high-risk

In total, 69% of respondents kept small flocks of mainly chickens, 71% indicated that they had no veterinarian to consult about their flock, and 54% said that wild birds could access their flock or its food or water. Respondents were generally experienced flock owners, with 29% having owned their flocks for at least 10 years, and 48% for three to 10 years. 

Education of backyard flock owners by health partners regarding signs and symptoms of avian influenza can help flock owners keep their flocks, themselves, and their families healthy.

Although 94% of owners were aware of avian flu, one third didn’t know the signs or symptoms in birds or people. About 90% knew the recommended precautions to take when handling sick or dead birds and said they were willing to use some types of personal protective equipment (PPE). A higher level of knowledge about avian flu was tied to increased intent to use PPE.

In total, 58% of respondents said that at least one person in their household was at increased risk for flu complications because of age, pregnancy, or underlying conditions.

“Education of backyard flock owners by health partners regarding signs and symptoms of avian influenza can help flock owners keep their flocks, themselves, and their families healthy,” the researchers wrote.