Multistate Outbreak of SARS-CoV-2 Infections, Including Vaccine Breakthrough Infections, Associated with Large Public Gatherings, United States

Abstract

During July 2021, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.617.2 variant infections, including vaccine breakthrough infections, occurred after large public gatherings in Provincetown, Massachusetts, USA, prompting a multistate investigation. Public health departments identified primary and secondary cases by using coronavirus disease surveillance data, case investigations, and contact tracing. A primary case was defined as SARS-CoV-2 detected <14 days after travel to or residence in Provincetown during July 3-17. A secondary case was defined as SARS-CoV-2 detected <14 days after close contact with a person who had a primary case but without travel to or residence in Provincetown during July 3-August 10. We identified 1,098 primary cases and 30 secondary cases associated with 26 primary cases among fully and non-fully vaccinated persons. Large gatherings can have widespread effects on SARS-CoV-2 transmission, and fully vaccinated persons should take precautions, such as masking, to prevent SARS-CoV-2 transmission, particularly during substantial or high transmission.

Keywords: COVID-19; COVID-19 vaccines; Massachusetts; SARS-CoV-2; United States; breakthrough infections; coronavirus disease; coronaviruses; disease outbreaks; multistate outbreak; respiratory infections; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Primary cluster-associated cases of severe acute respiratory syndrome coronavirus 2 infection (n = 1,098), by vaccination status and date of specimen collection, after large public gatherings in Provincetown, Massachusetts, USA, July 2021. Fully vaccinated persons were those who were >14 days after completion of all recommended doses of a US Food and Drug Administration‒authorized coronavirus disease vaccine (2 doses of Pfizer/BioNTech [https://www.pfizer.com] or Moderna [https://www.modernatx.com], or 1 dose of Johnson & Johnson [https://www.jandj.com]), with documentation in their state immunization information system or self-report of vaccination details during case investigation. Non–fully vaccinated includes persons who were partially vaccinated or unvaccinated or whose vaccination status was unknown.

Figure 2

Transmission diagram of primary (n = 26) and secondary (n = 30) cluster-associated cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, by vaccination status and date of symptom onset or specimen collection, after large public gatherings in Provincetown, Massachusetts, USA, July 2021. A primary case was defined as detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person <14 days after travel to or residence in Provincetown during July 3–17. A secondary case was defined as detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person <14 days after close contact (within 6 feet for a cumulative total of >15 minutes within a 24-hour period) with a person who had a primary case during their infectious period, and without history of travel to or residence in Provincetown during July 3–August 10. The infectious period of a person with a primary case was defined as 2 days before through 10 days after symptom onset or, if asymptomatic, 2 days before or through 10 days after a positive test result. A vaccine breakthrough case was a cluster-associated case in a person who completed all recommended doses of a US Food and Drug Administration‒authorized COVID-19 vaccine (2 doses of Pfizer/BioNTech [https://www.pfizer.com] or Moderna [https://www.modernatx.com], or 1 dose of Johnson & Johnson [https://www.jandj.com]) >14 days before collection of a SARS-CoV-2‒positive specimen. Gray shading indicates the event exposure period (July 3–17, 2021) in the primary case definition. Only primary cases associated with a secondary case are shown. Symptom onset of persons with secondary cases before symptom onset of persons with primary cases was observed in 4 pairs, consistent with previous reports (21,22), and could be caused by presymptomatic transmission (23,24) or variability in self-reported symptom onset date. Household contacts were exposed to persons who had a primary case within household settings. Settings of nonhousehold exposures were workplace (1), summer camp (2), social gatherings (4), shared ride (1), and unknown (1).

Figure 3

Time from completion of coronavirus disease (COVID-19) vaccination to date of specimen collection, by vaccine product, among fully vaccinated persons (n = 918) who had primary and secondary cluster-associated cases of severe acute respiratory syndrome coronavirus 2 infection after large public gatherings in Provincetown, Massachusetts, USA, July 2021. Fully vaccinated persons were those who were >14 days after completion of all recommended doses of a US Food and Drug Administration‒authorized COVID-19 vaccine (2 doses of Pfizer/BioNTech [https://www.pfizer.com] or Moderna [https://www.modernatx.com], or 1 dose of Johnson & Johnson [https://www.jandj.com]), with documentation in their state immunization information system or self-report of vaccination details during case investigation. Minimum time from completion of vaccination to specimen collection for persons who had breakthrough infections was 14 days. Median time from completion of vaccination to SARS-CoV-2‒positive specimen collection was 105 (range 15–326) days. Median times from completion to infection, by vaccine product, were 104 (range 15–326) days for persons who received the Pfizer-BioNTech vaccine, 104 (range 50–280) days for persons who received the Moderna vaccine, and 115 (range 23–225) days for persons who received the Johnson & Johnson/Janssen vaccine. Two persons were >270 days after vaccination at the time of specimen collection; 1 was vaccinated with Moderna 280 days before; and the other person with Pfizer-BioNTech 326 days before. Both persons were vaccinated through COVID-19 vaccine clinical trials.