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Pandemics and Biosecurity
24MAY

Ship hantavirus cluster is winding down

3 min read
16:06UTC

WHO bulletin DON604 put the MV Hondius Andes-virus cluster at an effective reproduction number of 0.7 on 22 May, with 13 cases and matching genomes confirming a single spillover. The 42-day all-clear window closes in mid-June.

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Key takeaway

The MV Hondius hantavirus cluster is winding down at an Rt of 0.7, with an all-clear due mid-June.

WHO bulletin DON604 put the effective reproduction number of the MV Hondius Andes-virus cluster at 0.7 as of 22 May 1. The MV Hondius is a Dutch-flagged Antarctic expedition cruise ship; Andes virus is the only hantavirus known to spread person to person, which is why this cluster drew formal WHO tracking at all. The effective reproduction number, or Rt, is the average number of further people each case infects; a value below one means an outbreak shrinks on its own.

The cluster added just one case since 24 May, reaching 13 in total . Near-identical genome sequences across patients confirm a single rodent-to-human spillover rather than scattered introductions 2. That genomic match is what rules out independent reintroductions, the signature that lets epidemiologists declare a cluster finished rather than merely paused.

The WHO holds the global risk at low. The 42-day quarantine window for the highest-risk contacts, set at twice the longest plausible incubation period, closes in mid-June; if no new case appears, the WHO can formally declare the outbreak over. Saying plainly that an outbreak is ending is as much the calibration job as flagging one that is not.

Deep Analysis

In plain English

Andes virus is an unusual type of hantavirus, a group of diseases spread by rodents, because it is the only one that can also spread between people through close contact. Thirteen people who travelled on the MV Hondius expedition cruise ship contracted Andes virus. Three died. The good news from WHO's 28 May bulletin is that the outbreak appears to be winding down. The effective reproduction number (Rt) has been measured at 0.7, which means each sick person is, on average, infecting fewer than one other person. When Rt stays below 1, an outbreak fades out naturally. The last significant exposure window closes around mid-June, when the 42-day monitoring period for the highest-risk contacts ends. Health authorities in 12 countries have been tracking contacts of infected passengers since the ship docked at Rotterdam in May.

What could happen next?
  • Opportunity

    Near-identical genome sequences from 13 cases confirming a single-spillover origin will provide the cleanest dataset available for modelling Andes virus person-to-person transmission risk in closed travel environments, directly informing future cruise-ship and expedition-vessel biosafety protocols.

Sources:World Health Organization
Mentions:World Health Organization →MV Hondius →DON 600 →ECDC →HCPS →South Korea →Patagonia →HAN00528 →Argentina →CDC →Andes virus →Trevor Bedford →El Bolsón →
First Reported In

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World Health Organization· 2 Jun 2026
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Causes and effects
Caused by
Hondius hantavirus cluster hits 12 cases
DON604's 13-case total is an increment from the 12-case cluster recorded at ID:3601, confirming the downward trajectory.
Occurred 24 May 2026
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Ship hantavirus cluster is winding down
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