The 34 infections wasnt from a single birthday party:

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 remaining 12 patients were each in contact with at least one previously symptomatic patient. Four patients (Patients 10, 29, 33, and 34) may have been infected by more than one person. 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.

This virus is not very contagious and it's rare. It is not as infectious as covid and unlikely to sustain transmission. This outbreak in particular is notable because of Patient 2 and his wife Patient 9. The later patients were also in frequent contact with multiple other patients when they were infected. If this incident only resulted in 34 infections, and that's the most unique super spreading event the virus has had. It's not worthy to freak out about andes like it's going to be another pandemic.