"The Andes hantavirus is as severe as the Ebola virus." The sentence from epidemiologist Antoine Flahault, reported by Le Parisien on 11 May 2026, circulated across news feeds within hours. It is accurate in terms of individual severity. And yet, on the same day, the WHO assesses the risk to the general population as low. How can these two statements hold together?
For the public confronted with the MV Hondius episode, untangling the confusion between severity and probability of exposure is essential. This article offers a measured read, based on official assessments from the WHO, ECDC and CDC, and on the scientific literature on the Andes virus.
Severity of the Andes virus: high
On individual severity, there is no debate. The Andes virus is one of the most lethal acute viral infections in immunocompetent humans.
| Pathogen | Case fatality | Source |
|---|---|---|
| Andes virus (HPS) | around 40% | CDC |
| Sin Nombre virus (HPS USA) | 30 to 35% | CDC |
| Ebola Zaire | 50 to 90% depending on strains | WHO |
| Ebola Sudan | 41 to 65% | WHO |
| Hantaan hantavirus (severe HFRS) | up to 15% | CDC |
| Puumala hantavirus (moderate HFRS) | < 1% | CDC |
| Seasonal influenza | around 0.1% | WHO |
| COVID-19 (2020-2023 variants) | 0.5 to 2% | WHO |
At the individual level, the case fatality of the Andes virus is high: per the CDC, hantavirus pulmonary syndrome is fatal for nearly 4 in 10 infected people. The comparison with Ebola, highlighted by Antoine Flahault, is defensible: both diseases cause rapid deterioration requiring immediate intensive care, with no licensed specific antiviral.
Severity is only half of the risk
The health risk of an infectious disease is the product of two variables:
Risk = Severity × Probability of exposure
A disease can be:
- Severe and frequent: high population impact. Historical example: pneumonic plague in endemic areas without treatment.
- Severe and unlikely: to be watched. Example: Ebola in Europe; or the Andes virus for the French general public.
- Mild and frequent: to be managed in the long run. Example: seasonal influenza.
- Mild and unlikely: negligible impact.
For the French population, the Andes virus falls into the second category: high individual severity, but very low probability of exposure.
Probability of exposure: why the general risk remains low
Three epidemiological features explain the WHO's "low" assessment for the general public.
1. Person-to-person transmission is rare
Person-to-person transmission remains the exception, and the CDC specifies that it is extremely rare: only the Andes virus has documented such a possibility. The vast majority of infections come from the reservoir rodent — the colilargo, Oligoryzomys longicaudatus — found only in Argentine and Chilean Patagonia.
The colilargo is not present in Europe. The house mouse and the brown rat of European cities are not carriers of the Andes virus.
2. Person-to-person transmission is not like influenza
When it does occur, Andes transmission requires close, prolonged contact with a symptomatic person: same household, direct care without protection, prolonged confined space. The Epuyén outbreak (Argentina, November 2018 – February 2019), documented in the New England Journal of Medicine by Martínez and colleagues, recorded 34 confirmed infections and 11 deaths, spread notably during confined social events (birthdays, weddings).
There is no airborne transmission over several metres as with influenza or COVID-19, no transmission via urban circulation, public transport or brief contacts. That is why wearing a mask is not recommended for the general public.
3. The long incubation enables active surveillance
The Andes virus has the longest incubation period in the hantavirus family: 7 to 42 days. This feature is paradoxically protective at the population scale:
- people potentially exposed can be identified and followed up over an extended window;
- the moment they become contagious (symptom onset) can be anticipated by surveillance;
- isolation occurs before the transmission chain widens.
This is exactly what France, the United Kingdom, the Netherlands and the United States are doing for MV Hondius passengers: 42 days of medical surveillance, immediate hospitalisation at the slightest alert. It is this scheme, and not a population measure, that contains the risk.
The right comparison: not Ebola in general, but Ebola outside an outbreak
When Antoine Flahault compares the Andes virus to Ebola, he is talking about individual severity. That is accurate.
But the population risk of Ebola depends on context:
- Ebola in an active epidemic area (Liberia 2014, Sierra Leone, Guinea, DRC): high risk, broad quarantine measures, border closures, MSF/WHO mobilisation.
- Ebola outside an epidemic area (e.g., an imported case in Madrid in 2014): population risk is low, because transmission requires close contact with the body fluids of a symptomatic patient. The few imported cases have systematically been contained without flare-ups.
The Andes virus in France falls into the second case. High individual severity, very low probability of collective exposure, contained by active surveillance of identified contacts.
The WHO assessment on the MV Hondius: "low risk"
In its statement of 7 May 2026, the WHO published its official assessment. Director-General Tedros Adhanom Ghebreyesus stated: "Although this is a serious incident, WHO assesses the risk to public health as low." The agency specifies that the Andes virus is the only hantavirus known for person-to-person transmission, which remains limited to close and prolonged contact. The ECDC, for its part, assesses the risk to the EU/EEA general population as "very low".
This assessment has not been revised since, despite the identification of:
- 1 confirmed case in France (11 May);
- 1 confirmed case in the United States (11 May);
- 8 + 14 contacts in France via return flights (11 May).
The scheme is doing its job: the cases that emerge are already under surveillance. That is the inverse of a scenario where cases would appear off-radar in the general population.
In practice: what to do?
If you belong to the general public
No specific measure. You can continue your activities normally. No mask, no distancing, no avoidance of public transport.
The only general precautions already recommended by the CDC for any hantavirus disease (Andes, Puumala and others) are the following:
- do not handle wild rodents, dead or alive;
- avoid closed, abandoned rural spaces without precaution;
- when cleaning a basement, attic or forest cabin possibly infested: spray diluted bleach (1:9), wear an FFP2 / N95 mask, gloves, and do not use a broom or a dry vacuum cleaner.
For more, see our decontamination breakdown.
If you are an identified MV Hondius contact
You have received (or will receive) a call from the health authorities. Follow the protocol communicated:
- temperature monitoring;
- self-isolation if requested;
- immediate consultation at the slightest symptom;
- emergency services (in France: 15 or 112) in case of urgency, always mentioning your exposure.
If you are a healthcare professional
The WHO/ECDC recommendations apply: FFP2/N95, impermeable gown, gloves, goggles or face shield for the management of any suspect or confirmed hantavirus case, particularly during aerosol-generating procedures (intubation, respiratory physiotherapy).
Summary
| Question | Answer |
|---|---|
| Is the Andes virus severe? | Yes — case fatality around 40%, comparable to Ebola at the individual level. |
| Is there a risk to the general public? | Low per the WHO, ECDC and CDC, assessment maintained. |
| Should I wear a mask on public transport? | No. |
| Is the follow-up serious? | Yes — about thirty identified and followed up in France, hospital care at Bichat, decree of 11 May. |
| Should the Ebola comparison worry me? | Understand the nuance: high individual severity, very low probability of exposure. |
The best thing for the general public is to stay informed through reliable sources, follow the recommendations of health authorities if identified as a contact, and avoid hasty conclusions drawn from comparisons taken out of their epidemiological context. The WHO, ECDC, CDC and Santé publique France publish regular updates accessible via our Sources page.