Open Letter to WHO: Hantavirus Outbreak
Editorial Note (May 8, 2026):
After this letter was sent, we found that the World Health Organization press release had been updated to replace “droplet precautions” with “transmission-based precautions during close contact.” The guidance, however, still does not recommend airborne precautions or respirator use (e.g., N95 respirators), and continues to recommend “medical masks.”
Dear Colleagues at the World Health Organization,
The present letter concerns the hantavirus outbreak onboard the MV Hondius cruise ship, and more particularly the World Health Organization press release regarding the practices to adopt in view of this outbreak (hereinafter the “Press Release”).
We express concern regarding the insufficiency of the precautionary measures described in the Press Release to control the potential spread of the virus. Sequencing has now confirmed that the virus involved is Andes hantavirus, a strain associated with documented human-to-human transmission. In order to reduce risk both to the general population and to those onboard the ship, heightened precautions should be adopted beyond those articulated in the Press Release.
- The Press Release states: “If respiratory symptoms are present to practice respiratory etiquette and wear a medical mask.”
- This does not account for the possibility of presymptomatic transmission during the prolonged incubation period associated with Andes virus infection. Published investigations of Andes virus outbreaks have identified transmission events occurring at or near symptom onset, raising concern that infectiousness may precede recognition of illness;
- In addition, aerosol or airborne transmission has not been ruled out and should therefore be accounted for in infection control measures, particularly given the high mortality associated with Andes hantavirus infection. Respirator use, not medical masks, is the appropriate standard to protect staff, passengers, and the general population, and to mitigate possible aerosol transmission;
- Finally, “respiratory etiquette” is not an adequate protective measure for a severe infectious disease associated with documented human-to-human transmission, regardless of the precise mechanism of transmission. The term is also vague and open to interpretation, and should be replaced with clear, specific guidance regarding effective protective measures.
- The Press Release states: “Standard precautions combined with droplet precautions during close contact are considered sufficient.”
- Given confirmed Andes hantavirus infection, documented human-to-human transmission, and the high mortality associated with the disease, protection against airborne transmission should be adopted in healthcare settings;
- The WHO is requested to provide the scientific basis for its conclusion that “standard precautions” and droplet precautions alone are sufficient in the context of this outbreak. If respiratory aerosol transmission has not been excluded, the WHO’s recommendations are insufficient to adequately protect healthcare workers, passengers, and the public.
- As inhalation of aerosolized rodent excreta is a recognized route of hantavirus transmission, we further urge the WHO to recommend measures to mitigate toilet plume contamination. Toilet flushing generates aerosol plumes which, if infectious virus is present following toilet use by an infected individual, may contribute to human-to-human transmission, particularly in poorly ventilated indoor spaces. Adding appropriate disinfectants prior to flushing may help reduce this risk.
Respectfully submitted,
Yaneer Bar-Yam
for the World Health Network Core Action Group
References:
1. Press Release, WHO May 5, 2026: https://www.who.int/emergencies/disease-outbreak-news/item/2026-DON599
2. Andes Virus information: Martínez, V. P. et al. (2020). “Super-spreaders” and person-to-person transmission of Andes virus in Argentina. New England Journal of Medicine, 383(23), 2230–2241. https://www.nejm.org/doi/full/10.1056/NEJMoa2009040
