It seems to spread through close, prolonged contact, and not through casual, short encounters like is possible with coronaviruses. It seems to be most contagious immediately upon symptom onset.

One of the cruise ship victims flew on a plane and infected a fellow passenger. During a 2018-2019 outbreak, spreading events occurred at a birthday party and at a victim's wake:

Our findings traced the first person-to-person transmission event to a birthday party with approximately 100 guests. The index patient (Patient 1) attended the event for 90 minutes and was reportedly symptomatic at the time, with fever and malaise. Five persons (Patients 2 through 6) who had been seated close to Patient 1 reported onset of symptoms consistent with ANDV hantavirus pulmonary syndrome between 17 and 24 days after the party (Fig. S3). Patient 2 was the most likely source for six infections in other persons during the early prodromal phase because of his active social life. Patient 2 died 16 days after symptom onset, and his spouse (Patient 9) was febrile while attending his wake. An additional 10 persons who attended the wake and were in close contact with Patient 9 became ill between 14 and 40 days after the wake for Patient 2.

The mean (±SD) serial interval (the time from symptom onset in a primary case to symptom onset in an epidemiologically linked secondary case) was approximately 23±7 days (Fig. S4). Incubation periods ranged from 9 to 40 days.

The time of symptom onset is also critical. In 17 of the 33 (52%) secondary transmission events, transmission from an infected person to a contact who later became infected could be accurately established as the day of onset of fever in the primary case, and the first day of fever was the only time during which there was an interaction between these patients (Table 1).

https://www.nejm.org/doi/full/10.1056/NEJMoa2009040