Epidemiological News: Week 1, 2026
Non-Communicable Disease and Healthcare System Developments
Pharmacovigilance Signals: CAR-T Therapies and Brain Oedema Risk
The Pharmacovigilance Risk Assessment Committee (PRAC) of the European Medicines Agency adopted recommendations during its November 2025 meeting concerning several safety signals with potential clinical implications. Most significantly, both axicabtagene ciloleucel and lisocabtagene maraleucel—chimeric antigen receptor T-cell (CAR-T) therapies used in haematological malignancies—have been flagged for an increased risk of brain oedema specifically among patients with primary mediastinal large B-cell lymphoma (PMBCL). Marketing authorisation holders have been requested to submit supplementary information by 5 February 2026. CAR-T therapies are already associated with cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome (ICANS), but this signal suggests that PMBCL patients may face elevated cerebral complications requiring enhanced monitoring protocols.
Valproate and Paternal Exposure: Neurodevelopmental Concerns
The PRAC continues its assessment of a signal concerning neurodevelopmental disorders in offspring following paternal exposure to valproate and related substances prior to conception. While maternal valproate exposure during pregnancy is an established teratogenic risk associated with neural tube defects and impaired cognitive development in offspring, the potential for paternal germline effects represents a novel pharmacovigilance concern. Supplementary information has been requested from the marketing authorisation holder with a deadline of 11 March 2026. Should this signal be confirmed, it would substantially alter prescribing guidance for valproate in men of reproductive age.
Cardiovascular Safety: Venlafaxine Cardiotoxicity Signal
A cardiotoxicity signal has been raised for venlafaxine, a widely prescribed serotonin-norepinephrine reuptake inhibitor. Venlafaxine is known to cause dose-dependent increases in blood pressure, but the current signal suggests broader cardiac effects requiring further characterisation. The marketing authorisation holder has been requested to provide supplementary data by 13 April 2026. Given venlafaxine’s extensive use in major depressive disorder and generalised anxiety disorder, any confirmed cardiotoxic effect would have substantial implications for benefit-risk assessments, particularly in patients with pre-existing cardiovascular conditions.
Progestogen-Only Contraceptives and Meningioma
The PRAC evaluated a signal linking desogestrel and etonogestrel—progestogen-only contraceptive agents—to meningioma risk. Intracranial meningiomas have previously been associated with other progestogen exposures, notably cyproterone acetate and chlormadinone acetate. At this stage, the committee determined that no action is required from marketing authorisation holders pending further evaluation. This signal merits continued surveillance given the widespread use of progestogen-only contraception.
Infectious Diseases: Global Perspective
Vector-Borne Transmission
Dengue: 2024 Global Summary and Implications for 2026
The WHO’s year-end Weekly Epidemiological Record confirmed that 2024 constituted the most severe global dengue burden on record, with 14,434,584 reported cases, 7,718,585 laboratory confirmations, 52,738 severe cases, and 11,201 deaths across all six WHO regions. This represents more than a three-fold increase compared to approximately 4.1 million cases reported in 2023, marking an unprecedented acceleration in dengue transmission dynamics.
Dengue fever, caused by four serotypes of the Flavivirus genus (DENV-1 through DENV-4) and transmitted primarily through Aedes aegypti and Aedes albopictus mosquitoes, has expanded from fewer than 10 endemic countries in the 1970s to over 130 today. The clinical spectrum ranges from asymptomatic infection through classical dengue fever—characterised by high fever, severe headache, retro-orbital pain, myalgia, and rash with an incubation period of 4–10 days—to life-threatening severe dengue with plasma leakage, haemorrhagic manifestations, and organ impairment. Secondary infection with a heterologous serotype substantially increases the risk of severe disease through antibody-dependent enhancement. There is no specific antiviral treatment; management relies on early recognition, supportive care with fluid management, and monitoring for warning signs of severe disease.
Regional Distribution: The Region of the Americas bore the overwhelming burden, accounting for over 90% of global cases. Brazil alone reported 10,266,017 cases and 6,321 deaths, with hyperendemic circulation of all four serotypes. Argentina recorded its largest epidemic to date with 581,559 cases and 408 deaths across 19 provinces. Mexico (558,846 cases), Colombia (320,982 cases), Paraguay (295,785 cases), and Peru (271,531 cases) also experienced historically high caseloads. The convergence of El Niño-associated heavy rainfall, high population density, and inconsistent vector control measures drove this explosive regional outbreak.
South-East Asia reported 798,690 cases with 2,400 deaths, with Indonesia (257,271 cases, 1,461 deaths), India (232,425 cases), Bangladesh (101,214 cases, 557 deaths), and Thailand (104,681 cases) experiencing substantial monsoon-related transmission surges.
First Autochthonous Transmission in Iran: In a significant epidemiological development, the Islamic Republic of Iran confirmed its first locally acquired dengue cases in June 2024. Two infections were initially identified in Bandar-Lengeh, Hormozgan Province, linked to established Aedes aegypti presence. By mid-July 2024, 12 locally acquired cases had been documented, marking Iran’s first indigenous dengue transmission and reflecting both vector establishment and increased population movement from endemic regions.
European Implications: The WHO European Region reported 1,603 cases, predominantly from endemic French overseas territories—Réunion (1,227 cases) and Mayotte (68 cases)—where year-round Aedes aegypti activity sustains transmission. Sporadic autochthonous transmission on mainland Europe included 213 cases in Italy, 85 in France, and 10 in Spain, consistent with recent annual patterns. The established presence of Aedes albopictus across southern Europe and its continued northward expansion necessitates integrated arboviral surveillance capacity.
The 2024 dengue surge underscores the climate sensitivity of this arbovirus, coinciding with El Niño weather anomalies that extended transmission seasons and geographic range. The concurrent circulation of all four serotypes across multiple regions, with DENV-3 predominating for the first time in a decade in Mexico and Central America during the latter half of 2024, raises concerns regarding increased severe disease risk among populations with prior heterologous exposure. WHO declared a Grade 3 dengue emergency from December 2023 through December 2024, activating the highest incident management level with coordination across all six regional offices.
Infectious Diseases: European Union/European Economic Area
Note: ECDC surveillance data for Week 01/2026 were not available at the time of this report. European-level findings are therefore limited to information from the WHO Weekly Epidemiological Record and EMA pharmacovigilance communications.
Infectious Diseases: Bulgaria
Fecal-Oral Transmission
Salmonellosis: Notable Increase from Low Baseline
Nine laboratory-confirmed salmonellosis cases were reported during Week 01, representing an eight-fold increase compared to the single case registered during the equivalent period in 2025, though showing a modest decrease of 2 cases from the preceding week. Salmonellosis, caused predominantly by Salmonella enterica serovars Enteritidis and Typhimurium in Europe, typically manifests 6–72 hours following ingestion of contaminated food—commonly eggs, poultry, or produce—with acute onset gastroenteritis characterised by diarrhoea, fever, and abdominal cramping, usually resolving within 4–7 days. Invasive disease with bacteraemia occurs in approximately 5% of cases, particularly among immunocompromised individuals, young children, and the elderly.
While the absolute numbers remain modest, the year-over-year trajectory merits attention, particularly for identifying potential point-source contamination events.
Gastroenteritis and Enterocolitis: Elevated Incidence
A total of 109 cases of gastroenteritis and enterocolitis were reported nationally, representing a 30% increase from the 84 cases during the same week in 2025 and an increase of 10 cases from the preceding week. Case classification revealed 52 possible, 52 probable, and 5 confirmed cases, indicating substantial clinical diagnosis without laboratory confirmation. The non-specific nature of this syndromic category encompasses multiple aetiologies including viral (norovirus, adenovirus), bacterial, and parasitic causes.
The winter period typically sees elevated gastroenteritis incidence, driven predominantly by norovirus circulation. The concurrent increase in confirmed salmonellosis and campylobacteriosis suggests that a proportion of these syndromic cases may have bacterial aetiology warranting enhanced laboratory investigation.
Campylobacteriosis: Emergence from Zero Baseline
Seven laboratory-confirmed campylobacteriosis cases were registered during Week 01, compared to zero cases during the equivalent week in 2025. Campylobacter, primarily C. jejuni and C. coli, represents the most frequently reported bacterial gastrointestinal pathogen in the European Union. Transmission occurs through consumption of contaminated poultry, unpasteurised milk, or cross-contaminated foods. Following an incubation period of 2–5 days, infection typically presents with watery or bloody diarrhoea, abdominal pain, and fever. While usually self-limiting, campylobacteriosis is associated with post-infectious complications including reactive arthritis and Guillain-Barré syndrome.
The appearance of seven cases where none were reported in the corresponding period of 2025 may reflect enhanced surveillance, changes in laboratory testing practices, or genuine increased exposure. Geographic distribution (all cases from Varna and Sofia city) suggests localised transmission or reporting patterns requiring further characterisation.
Shigellosis and Other Enteric Pathogens
A single laboratory-confirmed shigellosis case was reported from Varna, compared to zero cases during the same period in 2025. Single cases of yersiniosis (confirmed) and two cases of Escherichia coli infection were also documented. These sporadic cases do not indicate outbreak activity but warrant routine surveillance continuation.
Rotavirus gastroenteritis showed a marked decline with only 3 cases versus 21 during the same period in 2025, likely reflecting both seasonal variation and the impact of routine childhood rotavirus vaccination.
Respiratory and Droplet Transmission
Varicella: Expected Seasonal Activity Below Prior Year
Varicella (chickenpox) accounted for 278 cases during Week 01, representing a 47% decrease compared to 524 cases in the equivalent 2025 week and a reduction of 18 cases from the preceding week. Case classification comprised 22 possible, 230 probable, and 26 confirmed cases. Geographic distribution showed highest concentrations in Varna (58 cases), Sofia city (36 cases), and Plovdiv (25 cases).
Varicella-zoster virus, a highly contagious herpesvirus transmitted via respiratory droplets and direct contact with vesicular fluid, typically affects children aged 1–9 years in countries without universal vaccination programmes. The incubation period of 14–16 days is followed by prodromal fever and characteristic pruritic vesicular rash progressing through papular, vesicular, and crusting stages. While generally benign in immunocompetent children, complications include bacterial superinfection, pneumonia, and neurological sequelae. Adults, pregnant women, and immunocompromised individuals face substantially higher complication rates.
Bulgaria does not include varicella vaccination in its routine childhood immunisation schedule, resulting in continued endemic circulation with typical winter-spring seasonality. The year-over-year decrease likely reflects natural epidemic cycling rather than programmatic intervention.
Scarlet Fever: Declining Incidence
Fifteen scarlet fever cases were registered (1 possible, 12 probable, 2 confirmed), representing a 44% decrease from 27 cases in the same 2025 period. Scarlet fever, caused by group A Streptococcus pyogenes producing pyrogenic exotoxins, presents with fever, pharyngitis, and characteristic sandpaper-textured erythematous rash following a 1–3 day incubation period. European countries, including Bulgaria, have experienced cyclical increases in scarlet fever and invasive group A streptococcal disease since 2022; the current week’s figures suggest a return toward baseline incidence.
COVID-19: Stable Low-Level Circulation
Thirty-four confirmed COVID-19 cases were reported, virtually unchanged from 33 cases during the equivalent 2025 period and identical to the preceding week. This represents continued low-level endemic circulation without signals of substantial wave activity.
Vector-Borne Transmission
Tick-Borne Diseases: Seasonal Trough
Lyme borreliosis recorded 3 confirmed cases (Sofia city and Haskovo region) during Week 01, a slight decrease from 4 cases in the same 2025 period. The winter period represents the seasonal trough for tick-borne infections in Bulgaria, with Ixodes ricinus activity substantially reduced during cold months. No cases of Crimean-Congo haemorrhagic fever, tick-borne encephalitis, or West Nile fever were reported, consistent with vector seasonality.
Contact and Sexual Transmission
Syphilis: Four-Fold Year-Over-Year Increase
Four confirmed syphilis cases were reported during Week 01, representing a 300% increase compared to the single case in the equivalent 2025 period and an increase of 1 case from the preceding week. While small absolute numbers limit statistical inference, this signal aligns with broader European trends of increasing syphilis incidence, particularly among men who have sex with men and in association with HIV co-infection.
Syphilis, caused by Treponema pallidum, progresses through primary (chancre), secondary (rash, mucocutaneous lesions), latent, and potentially tertiary stages affecting cardiovascular and neurological systems. The incubation period averages 21 days (range 10–90 days). Congenital syphilis through vertical transmission causes severe fetal and neonatal morbidity; notably, no congenital syphilis cases were reported this week compared to 1 case in the same 2025 period.
Other Sexually Transmitted Infections
Single cases each of gonorrhoea and urogenital chlamydial infection were reported, consistent with prior-year figures. No new HIV diagnoses were registered during Week 01, compared to 10 cases in the preceding week, likely reflecting reporting lag associated with the holiday period.
Neuroinvasive Infections
One confirmed case of viral meningitis/meningoencephalitis was reported in Lovech region, a decrease from 3 cases during the same period in 2025. A single probable case of bacterial meningitis (unspecified aetiology) was documented in Ruse. No cases of pneumococcal, streptococcal, or Haemophilus influenzae meningitis were reported, compared to 1 pneumococcal and 1 H. influenzae case during the equivalent 2025 period. No invasive meningococcal disease was registered.
Report compiled from: Bulgarian National Centre for Public Health and Analyses weekly surveillance data (Week 01/2026); WHO Weekly Epidemiological Record No. 52, 26 December 2025; EMA PRAC recommendations on signals, November 2025 meeting.