Lead
In late February 2026, roughly 50 influenza scientists gathered at a Hilton in Istanbul for the World Health Organization’s biannual committee to recommend strains for the fall 2026 vaccine. The meeting processes global surveillance data, evaluates last season’s vaccine performance and proposes candidate viruses for manufacturers to begin production. Although the U.S. formally withdrew from the WHO in January 2026, the Centers for Disease Control and Prevention confirmed it would participate virtually, a move that surprised some observers given the recent policy shift. The committee’s decisions, due to be announced Friday, set a nine-month production clock for vaccine makers worldwide.
Key Takeaways
- About 50 international influenza experts met in Istanbul in late February 2026 to select vaccine strains for the fall 2026 season.
- The WHO Global Influenza Surveillance and Response System aggregates data from 130 countries and funnels samples to seven collaborating centers, including the CDC.
- Each year roughly 1 billion people are infected with influenza; vaccine strain selection is central to limiting that burden.
- The U.S. withdrew from the WHO in January 2026 but CDC staff attended the Istanbul meeting virtually, per HHS guidance.
- WHO temporarily saw a slowdown in sample shipments after the U.S. funding reduction but reported shipments have resumed as of February 11, 2026.
- Manufacturers need about nine months from strain recommendation to produce and distribute seasonal flu vaccines.
- Experts warn that reduced U.S. in-person participation and funding could erode U.S. influence on strain choice and weaken global surveillance over time.
Background
The WHO convenes a technical committee twice a year to advise which influenza strains should be included in vaccines for the coming northern and southern hemisphere seasons. That process depends on continuous viral sampling from clinics and labs in some 130 countries; samples are forwarded to a network of seven WHO collaborating centers that analyze viral evolution. Decisions made in these meetings directly inform manufacturers, who begin production once strain recommendations are announced.
The United States has been a major funder of WHO programs and a central scientific contributor to the surveillance network, with the CDC operating as one of the collaborating centers. In January 2026, the U.S. government announced a formal withdrawal from WHO, a move that disrupted funding flows for sample shipping and technical support. WHO officials reported a temporary dip in sample circulation but said shipments had resumed by February 11, 2026.
Main Event
Scientists in Istanbul reviewed genomic sequences, regional case trends and vaccine effectiveness data from the prior season to pick strains most likely to circulate in fall 2026. Committee members weighed which viruses were both epidemiologically relevant and feasible for large-scale production. CDC scientists, who historically attended such meetings in person and exerted substantial influence, took part remotely this session after HHS confirmed CDC participation would be technical and virtual only.
HHS framed CDC’s involvement as narrowly technical: sharing surveillance data, offering expertise and contributing to scientific discussions without altering the administration’s withdrawal stance. On the ground at the Hilton, conveners worked through detailed charts and lab reports each day, a reminder of the methodical — and sometimes tedious — work behind vaccine strain selection. Participants noted that in-person interactions can shape consensus and that virtual attendance creates a different dynamic.
WHO announced it would release the committee’s recommended strains on Friday; manufacturers will then begin tasks such as seed-virus preparation and scale-up. The production timeline — about nine months — means any uncertainty in the recommendation process has downstream effects on vaccine availability and match by the upcoming fall season. Some experts expressed concern that shifts in funding and representation could subtly shift which regional virus data are prioritized.
Analysis & Implications
The U.S. decision to withdraw from WHO funding and formal participation introduces both practical and diplomatic consequences for influenza preparedness. Practically, delays or reductions in sample shipments constrain the seven collaborating centers’ ability to detect emerging variants quickly, which in turn can reduce confidence in strain selection. Diplomatic effects include diminished U.S. clout in multilateral scientific forums; CDC’s historical role helped align global recommendations with U.S. surveillance priorities.
Even if CDC provides technical input remotely, in-person deliberation matters for consensus-building. Informal hallway conversations and face-to-face exchanges often surface context — such as localized outbreaks or production constraints — that raw data alone may not convey. If other countries perceive a gap in U.S. engagement, they may give less weight to CDC-preferred strains, potentially increasing mismatch risk for the American population.
There is also a funding angle. WHO previously subsidized shipment costs for samples; the U.S. withdrawal removed a major contributor to that pool. WHO’s statement that shipments have resumed signals short-term remediation, but experts caution that episodic fixes may not fully restore the steady, predictable funding stream the surveillance network needs to operate optimally. Over multiple seasons, that uncertainty could translate into weaker global situational awareness and slower detection of drifted or novel strains.
Comparison & Data
| Metric | Value |
|---|---|
| Countries providing surveillance data | 130 |
| WHO collaborating centers | 7 |
| Estimated annual influenza infections | ~1 billion |
| Time from recommendation to vaccine readiness | ~9 months |
This concise table highlights the scale and timing that make the WHO strain-selection process critical. The system’s reach — 130 countries feeding seven analysis hubs — depends on reliable logistics and funding. A change in either the flow of data or the perceived neutrality of deliberations can shift vaccine-match probabilities, with measurable consequences for morbidity and mortality during a given season.
Reactions & Quotes
Several public-health figures offered quick assessments of the U.S. participation choice and its implications.
“It’s really tedious — you have to review a lot to make the best choice,”
Dr. Dan Jernigan, former head of CDC NCEZID (2023–2025)
Jernigan emphasized the painstaking nature of strain selection and noted CDC’s historical influence in these meetings. He warned that absence from the room could reduce U.S. sway over final recommendations and that virtual attendance changes the conversational dynamics by which consensus forms.
“There is no other way to protect the nation when it comes to shared surveillance networks,”
Jennifer Nuzzo, epidemiologist, Director of the Pandemic Center, Brown University
Nuzzo framed participation as a practical necessity despite rhetorical opposition to multilateral institutions, saying real-world protection relies on interconnected data-sharing and collaboration.
“We have been able to resume shipments around the world,”
Maria Van Kerkhove, Interim Director, WHO Epidemic & Pandemic Threat Management
WHO officials acknowledged a temporary dip in sample circulation after funding disruptions but indicated logistics were being restored, a development observers said is necessary for the surveillance system to function.
Unconfirmed
- Extent of long-term funding shortfalls: WHO reported resumed shipments, but whether funding is restored to pre-withdrawal levels remains unclear.
- Magnitude of sample volume reduction: public statements note a dip in shipments, but precise global sample-count declines and regional gaps are not fully documented publicly.
- Future U.S. engagement plans: HHS confirmed technical participation for this meeting, but longer-term U.S. policy on WHO collaboration in subsequent seasons is not finalized publicly.
Bottom Line
The U.S. virtual participation in the Istanbul strain-selection meeting underscores a tension between declared policy and practical public-health needs. Flu vaccine recommendations rest on global data flows, expert deliberation and tight manufacturing timelines; interruptions in funding or in-person engagement can create downstream risks for vaccine match and availability. For Americans and for global populations, the most immediate outcome to watch is whether the recommended strains produce vaccines that are well matched by fall 2026.
Policymakers face a choice: maintain distance from multilateral organizations for political reasons, or sustain engagement to preserve influence and the operational integrity of surveillance systems that protect public health. Science-driven collaboration may feel at odds with recent political rhetoric, but for influenza control the operational reality remains that international networks are hard to replace.