On July 30, 2021, this report was posted online as an MMWR Early Release.
Catherine M. Brown, DVM1; Johanna Vostok, MPH1; Hillary Johnson, MHS1; Meagan Burns, MPH1; Radhika Gharpure, DVM2; Samira Sami, DrPH2; Rebecca T. Sabo, MPH2; Noemi Hall, PhD2; Anne Foreman, PhD2; Petra L. Schubert, MPH1; Glen R. Gallagher, PhD1; Timelia Fink1; Lawrence C. Madoff, MD1; Stacey B. Gabriel, PhD3; Bronwyn MacInnis, PhD3; Daniel J. Park, PhD3; Katherine J. Siddle, PhD3; Vaira Harik, MS4; Deirdre Arvidson, MSN4; Taylor Brock-Fisher, MSc5; Molly Dunn, DVM5; Amanda Kearns5; A. Scott Laney, PhD2 (View author affiliations)
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What is already known about this topic?
Variants of SARS-CoV-2 continue to emerge. The B.1.617.2 (Delta) variant is highly transmissible.
What is added by this report?
In July 2021, following multiple large public events in a Barnstable County, Massachusetts, town, 469 COVID-19 cases were identified among Massachusetts residents who had traveled to the town during July 3–17; 346 (74%) occurred in fully vaccinated persons. Testing identified the Delta variant in 90% of specimens from 133 patients. Cycle threshold values were similar among specimens from patients who were fully vaccinated and those who were not.
What are the implications for public health practice?
Jurisdictions might consider expanded prevention strategies, including universal masking in indoor public settings, particularly for large public gatherings that include travelers from many areas with differing levels of SARS-CoV-2 transmission.
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During July 2021, 469 cases of COVID-19 associated with multiple summer events and large public gatherings in a town in Barnstable County, Massachusetts, were identified among Massachusetts residents; vaccination coverage among eligible Massachusetts residents was 69%. Approximately three quarters (346; 74%) of cases occurred in fully vaccinated persons (those who had completed a 2-dose course of mRNA vaccine [Pfizer-BioNTech or Moderna] or had received a single dose of Janssen [Johnson & Johnson] vaccine ≥14 days before exposure). Genomic sequencing of specimens from 133 patients identified the B.1.617.2 (Delta) variant of SARS-CoV-2, the virus that causes COVID-19, in 119 (89%) and the Delta AY.3 sublineage in one (1%). Overall, 274 (79%) vaccinated patients with breakthrough infection were symptomatic. Among five COVID-19 patients who were hospitalized, four were fully vaccinated; no deaths were reported. Real-time reverse transcription–polymerase chain reaction (RT-PCR) cycle threshold (Ct) values in specimens from 127 vaccinated persons with breakthrough cases were similar to those from 84 persons who were unvaccinated, not fully vaccinated, or whose vaccination status was unknown (median=22.77 and 21.54, respectively). The Delta variant of SARS-CoV-2 is highly transmissible (1); vaccination is the most important strategy to prevent severe illness and death. On July 27, CDC recommended that all persons, including those who are fully vaccinated, should wear masks in indoor public settings in areas where COVID-19 transmission is high or substantial.* Findings from this investigation suggest that even jurisdictions without substantial or high COVID-19 transmission might consider expanding prevention strategies, including masking in indoor public settings regardless of vaccination status, given the potential risk of infection during attendance at large public gatherings that include travelers from many areas with differing levels of transmission.
During July 3–17, 2021, multiple summer events and large public gatherings were held in a town in Barnstable County, Massachusetts, that attracted thousands of tourists from across the United States. Beginning July 10, the Massachusetts Department of Public Health (MA DPH) received reports of an increase in COVID-19 cases among persons who reside in or recently visited Barnstable County, including in fully vaccinated persons. Persons with COVID-19 reported attending densely packed indoor and outdoor events at venues that included bars, restaurants, guest houses, and rental homes. On July 3, MA DPH had reported a 14-day average COVID-19 incidence of zero cases per 100,000 persons per day in residents of the town in Barnstable County; by July 17, the 14-day average incidence increased to 177 cases per 100,000 persons per day in residents of the town (2).
During July 10–26, using travel history data from the state COVID-19 surveillance system, MA DPH identified a cluster of cases among Massachusetts residents. Additional cases were identified by local health jurisdictions through case investigation. COVID-19 cases were matched with the state immunization registry. A cluster-associated case was defined as receipt of a positive SARS-CoV-2 test (nucleic acid amplification or antigen) result ≤14 days after travel to or residence in the town in Barnstable County since July 3. COVID-19 vaccine breakthrough cases were those in fully vaccinated Massachusetts residents (those with documentation from the state immunization registry of completion of COVID-19 vaccination as recommended by the Advisory Committee on Immunization Practices,† ≥14 days before exposure). Specimens were submitted for whole genome sequencing§ to either the Massachusetts State Public Health Laboratory or the Broad Institute of the Massachusetts Institute of Technology and Harvard University. Ct values were obtained for 211 specimens tested using a noncommercial real-time RT-PCR panel for SARS-CoV-2 performed under Emergency Use Authorization at the Broad Institute Clinical Research Sequencing Platform. On July 15, MA DPH issued the first of two Epidemic Information Exchange notifications to identify additional cases among residents of U.S. jurisdictions outside Massachusetts associated with recent travel to the town in Barnstable County during July 2021. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.¶
By July 26, a total of 469 COVID-19 cases were identified among Massachusetts residents; dates of positive specimen collection ranged from July 6 through July 25 (Figure 1). Most cases occurred in males (85%); median age was 40 years (range=<1–76 years). Nearly one half (199; 42%) reported residence in the town in Barnstable County. Overall, 346 (74%) persons with COVID-19 reported symptoms consistent with COVID-19.** Five were hospitalized; as of July 27, no deaths were reported. One hospitalized patient (agerange =50–59 years) was not vaccinated and had multiple underlying medical conditions.†† Four additional, fully vaccinated patients§§ aged 20–70 years were also hospitalized, two of whom had underlying medical conditions. Initial genomic sequencing of specimens from 133 patients identified the Delta variant in 119 (89%) cases and the Delta AY.3 sublineage in one (1%) case; genomic sequencing was not successful for 13 (10%) specimens.
Among the 469 cases in Massachusetts residents, 346 (74%) occurred in persons who were fully vaccinated; of these, 301 (87%) were male, with a median age of 42 years. Vaccine products received by persons experiencing breakthrough infections were Pfizer-BioNTech (159; 46%), Moderna (131; 38%), and Janssen (56; 16%); among fully vaccinated persons in the Massachusetts general population, 56% had received Pfizer-BioNTech, 38% had received Moderna, and 7% had received Janssen vaccine products. Among persons with breakthrough infection, 274 (79%) reported signs or symptoms, with the most common being cough, headache, sore throat, myalgia, and fever. Among fully vaccinated symptomatic persons, the median interval from completion of ≥14 days after the final vaccine dose to symptom onset was 86 days (range=6–178 days). Among persons with breakthrough infection, four (1.2%) were hospitalized, and no deaths were reported. Real-time RT-PCR Ct values in specimens from 127 fully vaccinated patients (median=22.77) were similar to those among 84 patients who were unvaccinated, not fully vaccinated, or whose vaccination status was unknown (median=21.54) (Figure 2).
Transmission mitigation measures included broadening testing recommendations for persons with travel or close contact with a cluster-associated case, irrespective of vaccination status; local recommendations for mask use in indoor settings, irrespective of vaccination status; deployment of state-funded mobile testing and vaccination units in the town in Barnstable County; and informational outreach to visitors and residents. In this tourism-focused community, the Community Tracing Collaborative¶¶ conducted outreach to hospitality workers, an international workforce requiring messaging in multiple languages.
The call from MA DPH for cases resulted in additional reports of cases among residents of 22 other states who had traveled to the town in Barnstable County during July 3–17, as well as reports of secondary transmission; further analyses are ongoing. As of July 3, estimated COVID-19 vaccination coverage among the eligible population in Massachusetts was 69% (3). Further investigations and characterization of breakthrough infections and vaccine effectiveness among this highly vaccinated population are ongoing.
The SARS-CoV-2 Delta variant is highly transmissible (1), and understanding determinants of transmission, including human behavior and vaccine effectiveness, is critical to developing prevention strategies. Multipronged prevention strategies are needed to reduce COVID-19–related morbidity and mortality (4).
The findings in this report are subject to at least four limitations. First, data from this report are insufficient to draw conclusions about the effectiveness of COVID-19 vaccines against SARS-CoV-2, including the Delta variant, during this outbreak. As population-level vaccination coverage increases, vaccinated persons are likely to represent a larger proportion of COVID-19 cases. Second, asymptomatic breakthrough infections might be underrepresented because of detection bias. Third, demographics of cases likely reflect those of attendees at the public gatherings, as events were marketed to adult male participants; further study is underway to identify other population characteristics among cases, such as additional demographic characteristics and underlying health conditions including immunocompromising conditions.*** MA DPH, CDC, and affected jurisdictions are collaborating in this response; MA DPH is conducting additional case investigations, obtaining samples for genomic sequencing, and linking case information with laboratory data and vaccination history. Finally, Ct values obtained with SARS-CoV-2 qualitative RT-PCR diagnostic tests might provide a crude correlation to the amount of virus present in a sample and can also be affected by factors other than viral load.††† Although the assay used in this investigation was not validated to provide quantitative results, there was no significant difference between the Ct values of samples collected from breakthrough cases and the other cases. This might mean that the viral load of vaccinated and unvaccinated persons infected with SARS-CoV-2 is also similar. However, microbiological studies are required to confirm these findings.
Event organizers and local health jurisdictions should continually assess the need for additional measures, including limiting capacity at gatherings or event postponement, based on current rates of COVID-19 transmission, population vaccination coverage, and other factors.§§§ On July 27, CDC released recommendations that all persons, including those who are fully vaccinated, should wear masks in indoor public settings in areas where COVID-19 transmission is high or substantial. Findings from this investigation suggest that even jurisdictions without substantial or high COVID-19 transmission might consider expanding prevention strategies, including masking in indoor public settings regardless of vaccination status, given the potential risk of infection during attendance at large public gatherings that include travelers from many areas with differing levels of transmission.
Hanna Shephard, Geena Chiumento, Nicole Medina, Juliana Jacoboski, Julie Coco, Andrew Lang, Matthew Doucette, Sandra Smole, Patricia Kludt, Natalie Morgenstern, Kevin Cranston, Ryan J. Burke, Massachusetts Department of Public Health; Sean O’Brien, Theresa Covell, Barnstable County Department of Health and the Environment; Marguerite M. Clougherty, John C. Welch, Community Tracing Collaborative; Jacob Lemieux, Christine Loreth, Stephen Schaffner, Chris Tomkins-Tinch, Lydia Krasilnikova, Pardis Sabeti, Broad Institute; Sari Sanchez, Boston Public Health Commission; Mark Anderson, Vance Brown, Ben Brumfield, Anna Llewellyn, Jessica Ricaldi, Julie Villanueva, CDC COVID-19 Response Team.
Corresponding author: Catherine Brown, email@example.com.
1Massachusetts Department of Public Health; 2CDC COVID-19 Response Team; 3Broad Institute, Cambridge, Massachusetts; 4Barnstable County Department of Health and the Environment, Massachusetts; 5Community Tracing Collaborative, Commonwealth of Massachusetts.
All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Stacey B. Gabriel reports receiving grants from CDC. Bronwyn MacInnis, Katherine Siddle, and Daniel Park report receiving grants from CDC and the National Institutes of Health. Taylor Brock-Fisher reports receiving a grant from the Community Tracing Collaborative. No other potential conflicts of interest were disclosed.
† As of May 2021, ACIP recommended that all adults aged ≥18 years receive any of the three COVID-19 vaccines available in the United States via Emergency Use Authorization from the Food and Drug Administration, including Pfizer-BioNTech, Moderna, and Janssen; persons aged ≥12 years are eligible to receive the Pfizer-BioNTech COVID-19 vaccine. Full vaccination is defined as receipt of 2 doses of the Pfizer-BioNTech or Moderna COVID-19 vaccines or 1 dose of Janssen COVID-19 vaccine ≥14 days before exposure.
§ Genomic sequencing was performed using Illumina NovaSeq using the NEB LunaScript RT ARTIC SARS-CoV-2 Kit. Novel mutations were not identified in the spike protein of the cluster-associated genomes compared with genomes collected during the same period from ongoing genomic surveillance efforts at Broad Institute. Raw and assembled genomic data are publicly available under NCBI BioProject PRJNA715749.
¶ 45 C.F.R. part 46, 21 C.F.R. part 56; 42 U.S.C. Sect.241(d); 5 U.S.C. Sect.552a; 44 U.S.C. Sect.3501 et seq.
** COVID-like symptoms were based on the Council of State and Territorial Epidemiologists surveillance case definition for COVID-19. https://ndc.services.cdc.gov/case-definitions/coronavirus-disease-2019-2020-08-05/
§§ One vaccinated, hospitalized COVID-19 patient had received the Pfizer-BioNTech vaccine and three had received the Janssen vaccine.
¶¶ The Community Tracing Collaborative is a multiorganization partnership that has supported COVID contact tracing and outbreak investigation in Massachusetts. https://www.mass.gov/info-details/learn-about-the-community-tracing-collaborativeexternal icon
*** A preliminary analysis matching cluster-associated COVID-19 cases with the state HIV case surveillance data identified 30 (6%) cases with verified HIV infection; all were virally suppressed, and none were hospitalized as a result of infection with SARS-CoV-2.
- CDC. COVID-19: SARS-CoV-2 variant classifications and definitions. Atlanta, GA: US Department of Health and Human Services, CDC; 2021. Accessed July 25, 2021. https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/variant-surveillance/variant-info.html
- Massachusetts Department of Public Health. COVID-19 response reporting. Boston, MA: Massachusetts Department of Public Health; 2021. Accessed July 25, 2021. https://www.mass.gov/info-details/covid-19-response-reportingexternal icon
- Massachusetts Department of Public Health. Massachusetts COVID-19 vaccination data and updates. Boston, MA: Massachusetts Department of Public Health; 2021. Accessed July 25, 2021. https://www.mass.gov/info-details/massachusetts-covid-19-vaccination-data-and-updates#daily-covid-19-vaccine-report-external icon
- Christie A, Brooks JT, Hicks LA, Sauber-Schatz EK, Yoder JS, Honein MA. Guidance for implementing COVID-19 prevention strategies in the context of varying community transmission levels and vaccination coverage. MMWR Morb Mortal Wkly Rep 2021;70:1044–7. https://doi.org/10.15585/mmwr.mm7030e2external icon
FIGURE 1. SARS-CoV-2 infections (N = 469) associated with large public gatherings, by date of specimen collection and vaccination status* — Barnstable County, Massachusetts, July 2021
Abbreviation: MA DPH = Massachusetts Department of Public Health.
* Fully vaccinated was defined as ≥14 days after completion of state immunization registry–documented COVID-19 vaccination as recommended by the Advisory Committee on Immunization Practices.
FIGURE 2. SARS-CoV-2 real-time reverse transcription–polymerase chain reaction cycle threshold values* for specimens from patients with infections associated with large public gatherings, by vaccination status† — Barnstable County, Massachusetts, July 2021§
Abbreviations: Ct = cycle threshold; RT-PCR = reverse transcription–polymerase chain reaction.
* Specimens were analyzed using a noncommercial real-time RT-PCR panel for SARS-CoV-2 performed under Emergency Use Authorization at the Clinical Research Sequencing Platform, Broad Institute of the Massachusetts Institute of Technology and Harvard University.
† Fully vaccinated was defined as ≥14 days after completion of state immunization registry–documented COVID-19 vaccination as recommended by the Advisory Committee on Immunization Practices.
§ Whiskers represent minimum and maximum observations; top of box represents the third quartile (Q3), bottom represents the first quartile (Q1), and box height represents the interquartile range. Midline is the median; “x” is the mean.
Suggested citation for this article: Brown CM, Vostok J, Johnson H, et al. Outbreak of SARS-CoV-2 Infections, Including COVID-19 Vaccine Breakthrough Infections, Associated with Large Public Gatherings — Barnstable County, Massachusetts, July 2021. MMWR Morb Mortal Wkly Rep 2021;70:1059-1062. DOI: http://dx.doi.org/10.15585/mmwr.mm7031e2external icon.
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The use of SARS in naming SARS-CoV-2 does not derive from the name of the SARS disease but is a natural extension of the taxonomic practice for viruses in the SARS species. The use of SARS for viruses in this species mainly refers to their taxonomic relationship to the founding virus of this species, SARS-CoV.
SARS-CoV-2 is a member of a large family of viruses called coronaviruses. These viruses can infect people and some animals. SARS-CoV-2 was first known to infect people in 2019. The virus is thought to spread from person to person through droplets released when an infected person coughs, sneezes, or talks.
If you have COVID-19, you can pass on the virus to other people for up to 10 days from when your infection starts. Many people will no longer be infectious to others after 5 days. You should: try to stay at home and avoid contact with other people for 5 days.
If you are a household or overnight contact of someone who has had a positive COVID -19 test result it can take up to 10 days for your infection to develop. It is possible to pass on COVID-19 to others, even if you have no symptoms.
Positive test results using a viral test (NAAT, antigen or other tests) in persons with signs or symptoms consistent with COVID-19 indicate that the person has COVID-19, independent of vaccination status of the person.
Severe acute respiratory syndrome (SARS) is a viral respiratory disease caused by a SARS-associated coronavirus. It was first identified at the end of February 2003 during an outbreak that emerged in China and spread to 4 other countries.
Like most respiratory viruses, SARS appeared to spread from person to person through coughing, sneezing and close contact. Symptoms of the infection seen during the 2003 outbreak included those similar to the flu: fever, cough, chills, fatigue, shortness of breath, headache and diarrhea.
COVID-19 is caused by a virus called SARS-CoV-2. It is part of the coronavirus family, which include common viruses that cause a variety of diseases from head or chest colds to more severe (but more rare) diseases like severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).
Seventeen years after the severe acute respiratory syndrome (Sars) outbreak and seven years since the first Middle East respiratory syndrome (Mers) case, there is still no coronavirus vaccine despite dozens of attempts to develop them.
Reinfection with the virus that causes COVID-19 means a person was infected, recovered, and then later became infected again. After recovering from COVID-19, most individuals will have some protection from repeat infections. However, reinfections do occur after COVID-19.
A negative result means it's likely you are not infectious. But a negative test is not a guarantee you do not have COVID-19 and there's still a chance you may be infectious. You should follow advice on how to avoid catching and spreading the virus.
How long do I need to isolate? People are thought to be most contagious early in the course of their illness. With Omicron, most transmission appears to occur during the one to two days before onset of symptoms, and in the two to three days afterwards. People with no symptoms can also spread the coronavirus to others.
Coronavirus Antibodies Fall Dramatically in First 3 Months after Mild Cases of COVID-19. A UCLA study shows that in people with mild cases of COVID-19, antibodies against SARS-CoV-2 — the virus that causes the disease — drop sharply over the first three months after infection, decreasing by roughly half every 36 days.
(2021). Naturally acquired SARS-CoV-2 immunity persists for up to 11 months following infection. The Journal of Infectious Diseases.
Kissing can pass COVID-19. Consider not kissing anyone you do not know or who you are not sure has been isolated for 14 days. Rimming, or any sexual activity that involves putting the mouth on the butt/anus, might pass COVID-19. The virus has been found in feces.
Any positive COVID-19 test means the virus was detected and you have an infection. Isolate and take precautions including wearing a high-quality mask to protect others from getting infected. Tell people you had recent contact with that they may have been exposed. Monitor your symptoms.
What is the COVID-19 antibody test? If you've been exposed to COVID-19 or vaccinated, your body produces antibodies as part of your immune response. This test checks for antibodies to COVID-19 after exposure or vaccination and provides a numerical value that indicates the level of antibodies present.
There's also a chance that a COVID-19 rapid antigen test can produce false-positive results if you don't follow the instructions carefully. False-positive results mean the test results show an infection when actually there isn't one.
The risk of SARS-CoV-2 transmission can be reduced by covering coughs and sneezes and maintaining a distance of at least 6 feet from others. When consistent distancing is not possible, face coverings may reduce the spread of infectious droplets from individuals with SARS-CoV-2 infection to others.
The coronavirus SARS-CoV-2 at the origin of COVID-19 shares more than 70% genetic similarity with SARS-CoV-1 that was at the origin of 2003 SARS. Infection-associated symptoms are very similar between SARS and COVID-19 diseases and are the same as community-acquired pneumonia symptoms.
The coronavirus that causes COVID-19 is similar to the one that caused the 2003 SARS outbreak. Since the 2019 coronavirus is related to the original coronavirus that caused SARS and can also cause severe acute respiratory syndrome, there is “SARS” in its name: SARS-CoV-2.
Transmission and incubation period of coronavirus - THL
SARS Coronavirus - an overview
Coronavirus disease (COVID-19): How is it transmitted?
Symptoms may appear 2-14 days after exposure to the virus. Anyone can have mild to severe symptoms. Possible symptoms include: Fever or chills.
People infected with flu typically develop symptoms 1-4 days after infection. Those with COVID-19 typically develop symptoms 3-4 days after being infected. However, people infected with COVID-19 can show symptoms as early as 2 days or as late as 14 days after infection.
A study conducted during high levels of Delta variant transmission reported an incubation period of 4.3 days,(2) and studies performed during high levels of Omicron variant transmission reported a median incubation period of 3–4 days.
- Breathing in air when close to an infected person who is exhaling small droplets and particles that contain the virus.
- Having these droplets and particles land on the eyes, nose, or mouth.
- Touching the eyes, nose, and mouth with hands that have the virus on them.