Pandemiology Watch (December 3-9, 2025)
MPOX
On December 5, 2025, the World Health Organization (WHO) highlighted that clade Ib mpox virus is spreading outside Africa. Since the second mpox Public Health Emergency of International Concern (PHEIC) ended on September 5, 2025, 43 cases have been confirmed across six WHO regions, with 24 occurring in people who had not recently travelled internationally, suggesting local transmission in Italy, Malaysia, the Netherlands, Portugal, Spain, and the United States. The report notes that men who have sex with men remain the most affected group, accounting for about half of the cases. Sexual contact is the main route of transmission, and many infections show few or no symptoms, which can allow the virus to spread undetected. WHO assesses the risk as moderate for men who have sex with men and low for the general population, emphasizing the need for ongoing surveillance, contact tracing, and access to medical care to manage complications.
UK.
On December 8, the UK Health Security Agency (UKHSA) reported the detection of a recombinant mpox virus in England in a person who recently returned from Asia. Genetic analysis revealed that the virus contains elements from both clade Ib and IIb, highlighting the virus’s ongoing potential to evolve. UKHSA emphasized the importance of continued genomic monitoring and has shared its findings with international partners, including the World Health Organization, to support global surveillance efforts.
H5N1
U.S.
On December 5, 2025, WHO announced the first confirmed human case of influenza A(H5N5) worldwide, detected in an adult with underlying conditions in Washington State. The case was notified on 15 November and confirmed by sequencing on 20 November. Genomic analysis showed that the virus belongs to the H5 haemagglutinin (HA) clade 2.3.4.4b. WHO underscored the need for continued global surveillance and genomic monitoring to track changes in avian influenza viruses. Based on current information, the overall public health risk from A(H5) viruses remains low, but low to moderate for individuals with occupational exposure to infected animals.
As of December 9, the Centers for Disease Control and Prevention reports has not reported any cases of person-to-person transmission of H5N1 in the United States. The total remains at 71 confirmed human cases and two deaths.
MEASLES
U.S.
On December 8, 2025, CIDRAP reported that measles outbreaks in South Carolina and Colorado are continuing to grow. South Carolina has identified eight new cases, bringing the state’s total to 87, most linked to the ongoing outbreak in the Upstate region. Colorado reported a case in an unvaccinated child in Montezuma County with no known exposure.
As of December 3, 2025, Center for Disease Control reports a total of 1,828 confirmed measles cases in the U.S. in 2025. 12 % of cases have required hospitalization (214 cases of 1,828), and three deaths have been reported.
Canada.
As of December 8, 2025, Canada has reported 5,298 measles cases where 71% occurred in children, according to the Public Health Agency of Canada. Ontario accounts for 45% of the cases, followed by Alberta with 37%. 89% were unvaccinated, and 7% required hospitalization. Genotype D8 remains the most frequently detected strain. 2 deaths have been reported.
Rift Valley Fever
Senegal.
On 5 December 2025, WHO reported that Senegal is facing a Rift Valley fever outbreak that has caused 500 human cases and 31 deaths as of 23 November. The virus has also heavily affected animals, with 425 confirmed cases and more than 2,000 abortions reported in herds. With support from WHO, authorities have strengthened surveillance, deployed rapid-response teams, and vaccinated over 40,000 animals to help control the spread. Most human infections have occurred among people who work closely with cattle, sheep, and goats.
Marburg
Marburg virus cases in Ethiopia have increased to 13, while the death toll remains at 8, according to CIDRAP on December 3. WHO is assisting the response with laboratory support, protective equipment and expanded community surveillance.
POLIO
As of December 3, 2025, the Global Polio Eradication Initiative reported new poliovirus detections in several countries. These include one cVDPV2 case in Angola, two cVDPV2 cases in DR Congo, and two cVDPV2-positive environmental samples in Chad. Additional detections this week were reported in Papua New Guinea, with seven cVDPV2-positive environmental samples.