Pandemic & Infectious Disease — 2026-04-01

Active Outbreak Tracker

Respiratory Viruses (COVID-19, Influenza, RSV) — United States

• Status: Low to declining activity nationally as the 2025–2026 respiratory season draws toward a close
• Key Development: The CDC's Center for Forecasting and Outbreak Analytics (CFA) continues to publish Rt estimates for COVID-19, influenza, and RSV across U.S. states. The CDC has also indicated it does not anticipate producing additional seasonal outlook updates for the remainder of the 2025–2026 respiratory season, suggesting activity levels have stabilized.
• Response: Year-round COVID-19 and RSV surveillance remains active. California continues RSV immunization with monoclonal antibodies (nirsevimab and clesrovimab) for eligible infants and children through April 30, 2026.

6 sources

cdc.gov

cdc.gov

cdc.gov

Respiratory Illnesses Data Channel | Respiratory Illnesses | CDC

cdc.gov

cdc.gov

cdc.gov

Measles Cases and Outbreaks | Measles (Rubeola) | CDC

cdc.gov

Weekly US Influenza Surveillance Report: Key Updates for Week 8, ending February 28, 2026 | FluView

cdc.gov

Global Measles Outbreaks | Global Measles Vaccination | CDC

Measles — United States & Global

• Status: Ongoing outbreaks; CDC updates confirmed U.S. case counts weekly
• Key Development: The CDC's measles data page was updated within the past week, reflecting continued domestic case tracking. Globally, the CDC's top-10 country tracker identifies active measles outbreaks worldwide, with vaccination gaps remaining a primary driver of spread.
• Response: CDC continues weekly surveillance updates and global vaccination monitoring. International outbreak response efforts are ongoing in high-burden countries.

6 sources

cdc.gov

cdc.gov

cdc.gov

Respiratory Illnesses Data Channel | Respiratory Illnesses | CDC

cdc.gov

cdc.gov

cdc.gov

Measles Cases and Outbreaks | Measles (Rubeola) | CDC

cdc.gov

Weekly US Influenza Surveillance Report: Key Updates for Week 8, ending February 28, 2026 | FluView

cdc.gov

Global Measles Outbreaks | Global Measles Vaccination | CDC

Lyme Disease — United States (Emerging Season)

• Status: Tick season escalating; Michigan reports a 168% increase in cases over five years
• Key Development: With Lyme disease season approaching its peak in the Northeast and Midwest, prevention efforts are intensifying. A new oral prophylactic — TP-05 (lotilaner) by Tarsus Pharmaceuticals — enrolled its first participant in the Phase 2 CALLIOPE trial on March 31, 2026. The investigational tablet is designed to kill Lyme-infected ticks before disease transmission occurs, representing a first-of-its-kind oral prophylactic approach.
• Response: The first participant was dosed in the CALLIOPE trial on March 31, 2026. The Pfizer/Valneva VLA15 vaccine candidate (now entering the FDA approval pathway following Phase 3 VALOR trial results showing >70% efficacy) also represents a significant development in the prevention pipeline.

Vaccine & Treatment Pipeline

• COVID-19 Vaccine Antigen Composition (2026–2027 formulation) (WHO TAG-CO-VAC): The WHO Technical Advisory Group on COVID-19 Vaccine Composition published a formal data call on March 30, 2026, requesting submissions to inform May 2026 deliberations on vaccine antigen composition. The group is monitoring SARS-CoV-2 variant evolution, immune responses to infection and vaccination, and real-world vaccine performance against circulating strains. Manufacturers and researchers are asked to submit data ahead of the May meeting.

• TP-05 (lotilaner) — Oral Lyme Disease Prophylactic (Tarsus Pharmaceuticals): Phase 2 CALLIOPE trial dosed its first participant on March 31, 2026. The novel oral tablet is designed to kill Lyme-infected ticks upon biting before they can transmit the Borrelia burgdorferi bacterium, distinguishing it from vaccine-based approaches currently in development.

• VLA15 (Lyme Disease Vaccine) (Pfizer / Valneva): Following Phase 3 VALOR trial results showing over 70% efficacy across participants aged 5 and older — announced the week of March 23, 2026 — Pfizer is proceeding with an FDA approval filing. The vaccine demonstrated a strong safety profile and no major concerns, despite falling short of its primary statistical endpoint due to lower-than-expected case counts in the trial. Coverage discussion has been boosted by reports of Lyme disease case surges, including a 168% increase in Michigan over five years.

Expert Analysis

A newly published commentary in The Lancet is calling on world leaders to elevate spillover prevention — the process by which pathogens jump from animals to humans — on the agenda of the upcoming 2026 UN High-Level Meeting on pandemic prevention, preparedness, and response (PPPR). The authors argue that despite the catastrophic lessons of COVID-19, "global attention has waned amid inflation, war, and challenges tied to" other geopolitical crises, creating dangerous gaps in preparedness. The piece stresses that the origins of most major pandemic threats lie at the human-animal interface and that durable prevention frameworks must address root drivers, not just outbreak response.

The timing is notable: the WHO's TAG-CO-VAC is already in active preparation for May 2026 vaccine composition decisions for COVID-19, underscoring that the immediate post-pandemic period remains an ongoing management challenge, not a resolved one. The WHO has previously noted that while some pandemic preparedness infrastructure has improved since 2020, "the world is not adequately prepared" for the next novel pathogen event — a concern that the Lancet commentary reinforces by framing spillover prevention as an underinvested pillar of the global health security architecture.

Meanwhile, the tick-borne disease front offers a constructive counterpoint: an active, diversified prevention pipeline — including a promising vaccine candidate and a first-of-its-kind oral prophylactic entering Phase 2 — demonstrates what coordinated investment in emerging infectious disease threats can achieve. Health security analysts have flagged tick-borne diseases as a bellwether category given their sensitivity to climate-driven geographic expansion, with Lyme-carrying tick populations now documented in regions where they were historically absent.

Global Health Security

WHO COVID-19 Vaccine Composition Process Advances: On March 30, 2026, the WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) published its formal data request to inform the May 2026 antigen composition deliberations. The call covers genetic and antigenic variant surveillance, immune response data from both infection and vaccination, and vaccine performance against currently circulating strains. This is a critical annual regulatory moment that shapes which antigens national immunization programs worldwide will procure for the next season.

UN High-Level Meeting on PPPR — Spillover Prevention Advocacy: A Lancet commentary published this week urges governments and multilateral institutions to place animal-to-human spillover prevention at the center of the 2026 UN High-Level Meeting on pandemic prevention, preparedness, and response. The authors warn that political momentum generated by COVID-19 has faded and that structural reforms — particularly around wildlife trade regulation, land-use change, and One Health surveillance — risk being deprioritized ahead of the meeting.

California Extends RSV Immunization Coverage Through April 2026: The California Department of Public Health has confirmed that RSV immunization with monoclonal antibodies (nirsevimab and clesrovimab) for eligible infants and children remains in effect through April 30, 2026, with insurance coverage of the immunization continuing for the full program period.

What to Watch Next

• WHO May 2026 COVID-19 Vaccine Composition Decision: The TAG-CO-VAC data submission window is now open ahead of deliberations expected in May. The outcome will determine which SARS-CoV-2 antigen(s) are recommended for next-season vaccines — a decision with major implications for manufacturers, procurement timelines, and public health campaign planning globally.

• Lyme Disease Season Escalation: With peak tick activity approaching in the northeastern and midwestern United States — and case counts up dramatically in states like Michigan — the coming weeks will test both clinical surveillance systems and public awareness campaigns. The entry of two distinct preventive approaches (VLA15 vaccine and TP-05 oral tablet) into late-stage development makes 2026 a pivotal year for Lyme disease prevention, though neither is yet approved.

• 2026 UN High-Level Meeting on Pandemic Preparedness: Advocacy by The Lancet and other public health bodies is intensifying around the scope and ambition of the upcoming PPPR high-level meeting. Whether spillover prevention, One Health frameworks, and binding international health security commitments make it into final agreed language will be a key indicator of whether COVID-era political momentum has been translated into lasting institutional change.