The Centers for Disease Control and Prevention (CDC) and state partners from Florida and New York yesterday reported their clinical findings on 21 imported Oropouche virus cases reported this summer. The team's early online report appears in Morbidity and Mortality Weekly Report (MMWR).

The disease, spread by biting midges and perhaps some mosquito species, has been spreading beyond endemic areas of South America since the end of 2023, fueling outbreaks and reports of severe fetal outcomes following infection during pregnancy. Earlier this month, the CDC issued Oropouche virus alerts for clinicians and travelers.

Of the 21 cases confirmed in the United States, 20 were in Florida and 1 in New York state. All of the patients had traveled to Cuba. Three people were hospitalized, but no deaths were reported. Similar imported cases have been reported in European travelers.

Cases continue to rise in Florida, which has now reported 30 imported Oropouche cases, according to the latest vectorborne illness report from the Florida Department of Health.

Relapsing symptoms a unique Oropouche feature

Most patients had a self-limiting febrile illness with headache and muscle aches, a clinical picture that is similar to other arboviral disease, including dengue, Zika, and chikungunya. Some Oropouche patients reported gastrointestinal symptoms.

At least three patients, however, sought care when they had relapsing symptoms, which the authors said is a unique feature of Oropouche virus infection. 

The CDC said the risk for sustained local transmission is low, and it urged people who have been in Oropouche-affected areas, including those experiencing symptoms, to take steps to avoid insect bites for 3 weeks after returning home. 

Studies are under way to see of US biting midge and mosquito species are capable of carrying the virus, and the CDC said it working with the Pan American Health Organization and other partners to learn more about infection risks during pregnancy.

A new study of the Jynneos two-dose mpox vaccine shows it was 80% effective in preventing infection among recipients in the United Kingdom in 2023, according to research published yesterday in Emerging Infectious Diseases. Of note, no one who was vaccinated was hospitalized with the viral disease. 

By 2023, the peak of mpox activity primarily among men who have sex with men (MSM) in the United Kingdom had passed, with only 137 cases reported during the year. Cases were recorded through the UK Health Security Agency, as mpox is a notifiable disease in the country.

To examine efficacy of the vaccine against infection mostly among MSM, the authors estimated the proportion of MSM vaccinated by matching each case to the one- and two-dose coverage at the time, 2 weeks before the men contracting mpox, then averaging the matched coverage across cases. 

One-dose protection 84%

Of the 137 case-patients, 47% reported no travel outside the United Kingdom in the 21 days before symptom onset, indicating likely acquisition in the United Kingdom. Most case-patients identified as MSM (78%), the authors said, though another 21 were adult men without recorded information about sexual orientation and no travel to mpox-endemic countries. Nine case-patients were excluded from the final analysis, 8 of whom linked to an mpox-endemic country.

Vaccine efficacy (VE) of one dose of Jynneos was estimated at 84% (95% confidence interval [CI], 74% to 91%) and the VE after dose two was 80% (95% CI, 69% to 83%).

Our finding is corroborated by a global case series that found illness among vaccinated persons to be less severe.

"Among known vaccinated case-patients in 2023, none were hospitalized. Of 11 (9%) persons who required hospital treatment for mpox, 9 were unvaccinated and vaccination status was unknown for 2," the authors said. "Our finding is corroborated by a global case series that found illness among vaccinated persons to be less severe."