The HealthyTravel team wishes you a Merry Christmas and a happy 2026 with travels in good health.

The US CDC has updated the areas at risk for chikungunya. As of 16 December, there is a chikungunya travel health notice for outbreaks in:

• Bangladesh
  
• Cuba
  
• Guangdong Province, China
  
• Sri Lanka
  

Countries considered to have an elevated risk for chikungunya include:

• Brazil
  
• Bolivia*
  
• Colombia
  
• India
  
• Mexico
  
• Nigeria
  
• Pakistan
  
• Philippines
  
• Thailand
  

*According to news (see under ‘Bolivia’) increased transmission is also seen in Bolivia.

Although global activity remains within expected seasonal ranges, early increases and higher activity than typical at this time of year have been observed in some regions.

Seasonal influenza viruses, including A(H3N2) viruses, continually evolve over time. Since August 2025, there has been a rapid increase of A(H3N2) J.2.4.1 alias K subclade viruses detected from several countries based on available genetic sequence data. These subclade K viruses have several changes from related A(H3N2) viruses. Current epidemiological data do not indicate an increase in disease severity, although this subclade marks a notable evolution in influenza A(H3N2) viruses. Early estimates suggest that the influenza vaccine continues to provide protection against hospital attendance in both children and adults, even though its effectiveness against clinical disease during the current season remains uncertain.

Media, citing local health authorities, report that the Departmental Health Service (Sedes) has issued a health alert following an active chikungunya outbreak in the Cochabamba tropics. Rubén Castillo, Head of Epidemiology, confirmed 100 cases, 81 of which are locally acquired, along with 40 suspected cases currently under investigation. The cases are primarily concentrated in the municipalities of Entre Ríos, Villa Tunari, and Puerto Villarroel. Authorities warned that transmission in the region continues to rise.

According to the European Center of Disease Control, chikungunya cases have been reported from six of nine departments with Santa Cruz to be the most affected one.

In 2025, Hong Kong reported 11 locally acquired chikungunya cases as of 10 December 2025. Six of these were epidemiologically linked to the Tsing Yi Nature Trails, and genetic analysis revealed identical viral sequences, suggesting ongoing local transmission.

Surveillance data from ECDC’s European Respiratory Virus Surveillance Summary (ERVISS) platform and PAHO indicate continued co-circulation of influenza viruses, respiratory syncytial virus (RSV) and SARS-CoV-2 at the start of the 2025–26 Northern Hemisphere winter. In Europe, influenza A predominates with increasing hospitalizations among older adults, while RSV circulation is rising in several countries. SARS-CoV-2 activity persists at lower but stable levels. In the Americas, early-season increases in influenza and RSV activity have been reported following a severe 2025 Southern Hemisphere season.

CDC’s Vessel Sanitation Program reports an outbreak of acute gastroenteritis due to norovirus aboard the AIDAdiva during a journey from 10 November to 16 December 2025. The number of ill passengers exceeded the reporting threshold, prompting investigation and enhanced control measures.

ECDC reports at least 193 Shigella sonnei infections in travelers returning from Cabo Verde in 2025, with most cases linked to all-inclusive resorts in Sal and Boa Vista. The outbreak strain shows resistance to trimethoprim with limited additional resistance markers.

Shigellosis outbreaks in Cape Verde have been reported in recent years, including among travelers.

Ticino health authorities reported the first locally acquired human West Nile virus (WNF) infection in Switzerland on 4 December 2025, in a resident who developed meningoencephalitis after mosquito exposure during summer. Previous detections of WNV in mosquitoes in Ticino suggested an established seasonal risk.