Chickenpox Outbreak Among Newly Arrived Migrants in New York City, 2022–2024

By Krishika A. Graham and colleagues, New York City Department of Health and Mental Hygiene, with CDC, NYC Health + Hospitals and the NYC Department of Homeless Services. Morbidity and Mortality Weekly Report (MMWR).

In brief

• What happened: in October 2022, New York City's health department (DOHMH) found a varicella (chickenpox) outbreak among people who had recently migrated from or through Central and South America and lived in city shelters or residential facilities. It was still going on.
• Who: 53% of cases were aged 4–18, and 92% had no record of varicella vaccination.
• Where it spread: mostly in shelters and residences (41.3%) or before arrival (39.4%); schools accounted for only 1.2%.
• Response: about 27,000 doses of varicella-containing vaccine given to newly arrived children, adolescents and adults.

Background

Varicella causes an itchy rash over the body and spreads through the air, droplets and contact. It is usually mild to moderate, but can cause pneumonia and death. The vaccine is highly effective.

Since spring 2022, New York City has taken in about 180,000 migrants, many seeking asylum; about 65,000 lived in city-run shelters and residential facilities. Many come from countries whose routine immunization programs do not include varicella vaccine, or were disrupted. In October 2022, DOHMH found three cases in a residential facility, and an outbreak followed.

Finding cases

Individual varicella cases were not reportable in NYC before 2024, but outbreaks of three or more were. DOHMH alerted emergency departments, hospitals and health centers. An outbreak case meant a typical rash plus a diagnosis or known exposure, in someone who had migrated from or through Central or South America since June 2022, or was linked to someone who had. Cases came from providers, shelters and schools, plus interviews, lab reports and syndromic surveillance of emergency-department visits.

Cases by week of rash onset and source of transmission, September 2022–March 2024. Chart: CDC.

The cases

As of March 8, 2024: 873 cases, with rash onset from September 12, 2022, to March 6, 2024.

• Ages: median 11 years (2 weeks to 70 years): 17.5% under 4, 53.0% aged 4–18, 29.4% adults.
• Unvaccinated: 802 (91.9%) had no record of vaccination.
• Hospitalized: 28, median age 22: 15 for complications (encephalitis, pneumonia, bacteremia, skin superinfection), 3 for evaluation, 10 for isolation or observation.
• Pregnancy: nine patients were pregnant; five delivered in NYC with normal newborn exams; four were treated with acyclovir.
• Deaths: none.

How it spread

Of 780 cases (89.3%) with a known source:

Patients lived in 105 shelters and residences, with a median of three cases each (1–197). One large family residence of about 950 rooms had 197 cases (22.6%), most during the first peak (December 2022–February 2023). Its outbreak ended after a vaccination campaign raised the share of children with immunity from 28% in December 2022 to over 80% in February 2023. (An outbreak ended after two incubation periods, 42 days, with no new case.)

The response

• Isolation and quarantine: rapid reporting, isolation of cases and quarantine of susceptible contacts.
• Pregnant contacts: checked for immunity; those without it were referred for varicella zoster immune globulin (VariZIG).
• Closures: from February 2023, sites with ongoing spread were closed to new residents for a time.
• Vaccination: on-site vaccinators gave all routine childhood vaccines, pairing varicella with MMR so that neither live vaccine had to wait the required 28 days, plus flu and COVID-19 vaccines. Of about 27,000 doses, DOHMH vendors gave more than 2,900 and NYC Health + Hospitals more than 24,000.
• Outreach: door-to-door education in shelters and links to community health centers for primary care.

Why schools stayed safe

About two-thirds of cases were school-aged, yet schools saw little spread. The likely reason: New York State requires 2 doses of varicella vaccine for grades K–12, and NYC kindergarten coverage in 2021–22 was 96.7%. Many migrants, by contrast, come from tropical countries where fewer young adults are immune.

For public health

• Vaccinate along the way: access to varicella and other vaccines throughout migrants' journeys, including at NYC's arrival center, could cut importations.
• Build capacity for fast, large-scale vaccination of new arrivals from countries without routine varicella vaccination.
• Find cases with syndromic surveillance and electronic lab reports where single cases are not reportable.

Sources

Based on "Varicella Outbreak Among Recent Arrivals to New York City, 2022–2024," Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention; MMWR material is in the public domain.