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Over a two-week period in early July 2021, nearly three-quarters of almost 500 COVID-19 cases that occurred in Provincetown, Massachusetts, were reported in fully vaccinated individuals, according to a report published by the Centers for Disease Control and Prevention (CDC).
The news made headlines in credible news sources like The Washington Post, MedPage Today, and CNBC. Some social media users misconstrued the statistic to suggest that meant COVID-19 vaccinations didn’t work, including the following sent to our team by Snopes readers:
A closer look at the report revealed that, overall, the statistics were true: Between July 3 and 18, 469 COVID-19 cases were identified among people who had traveled to the seaside town, and of those, 346, or 74%, occurred in fully vaccinated persons. However, the CDC was quick to note in the report at least four limitations to the dataset, and that rendered the report “insufficient to draw conclusions about the effectiveness of COVID-19 vaccines against SARS-CoV-2.”
We’ll get to those limitations in a bit. But first, a look at what the report found.
The report was posted online as an early release on July 30 and formally published on Aug. 6 in the CDC Morbidity and Mortality Weekly Report, a weekly digest of epidemiological updates published by the agency on a weekly basis.
In it, the CDC wrote that “summer events … attracted thousands of tourists” from across the country between July 3 and 18 in Barnstable County, though it did not explicitly state a town. Although it wasn’t mentioned specifically in the report, the increase in caseload corresponded with both the July Fourth holiday weekend and what is known as “Bear Week,” an annual Provincetown event that occurred in 2021 between July 10 and 18. Bear Week is described by the local events board as “one of the largest, busiest theme weeks” that attracts “tens of thousands of men.”
By the Numbers: Case Counts and Vaccination Rates
Beginning July 10, the Massachusetts Department of Public Health began receiving reports of an increase in COVID-19 cases, many of whom had attended “densely packed indoor and outdoor events at venues that included bars, restaurants, guest houses, and rental homes.” In response, state health officials used the COVID-19 surveillance system to identify a cluster of cases in Barnstable County that were then matched against the state’s vaccination registry.
By July 20, a total of 469 COVID-19 cases were identified among residents who had traveled to the area. Of those, 346 (74%) were reported in people who had been fully vaccinated. Specimens were collected from 133 of those vaccinated individuals, and testing revealed that 90% were positive for the highly infectious Delta variant. By comparison, the CDC estimates that as much as 93% of COVID-19 cases around the world are due to the Delta variant.
Overall, about 69% of those who attended the Barnstable event were vaccinated. Most of the breakthrough infections occurred in males (85%) in their early 40s; 46% had received the Pfizer-BioNTech vaccine, 38% the Moderna, and 16% the Johnson & Johnson.
Seventy-nine percent of vaccinated people who experienced a breakthrough infection were asymptomatic, most of whom described having a cough, headache, sore throat, and fever.
In total, no deaths were reported, but five patients were hospitalized — four of whom were fully vaccinated. One person in his or her 50s was not vaccinated and was hospitalized with multiple underlying medical conditions. All of the four vaccinated individuals were between 20 and 70 years old, and two were hospitalized with underlying medical conditions.
Looking at the Limitations
But before jumping to conclusions about the efficacy of the three COVID-19 vaccines available in the U.S., it is important to look closely at four limitations presented in the study.
“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,” wrote the health agency.
Secondly, asymptomatic breakthrough infections are likely underrepresented due to a statistical principle known as “detection bias.” For example, a person who is vaccinated and experiencing symptoms may choose not to get tested because he or she assume immunity to the virus and perhaps are simply suffering from a cold. Demographics of the infected individuals may also be skewed. The events, according to the CDC, were marketed to adult male participants who could be more prone to underlying health conditions, including immuno-compromising conditions. In short, it would be inaccurate to draw generalizing conclusions about the results for broader populations.
Interpreting the Results as Variants Continue to Emerge
Contrary to misleading social media posts, the CDC contends that its findings further provide evidence that variants of the SARS-CoV-2 continue to emerge, heightening the need for more robust prevention measures.
“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,” wrote the CDC.
As of May 2021, the Advisory Committee on Immunization Practices recommended that anyone over 18 receive one of three COVID-19 vaccines available in the U.S. under an Emergency Use Authorization from the U.S. Food and Drug Administration. As of this writing, The CDC still recommends that vaccination is the “most important strategy to prevent severe illness and death.”
In response to emerging variants, in July the CDC reversed its policy on wearing masks indoors in places with high COVID-19 transmission rates, including those who are fully vaccinated, in response to the Delta variant. The findings also suggest that areas without high COVID-19 transmission might consider expanding mask mandates in indoor public areas regardless of vaccination status, particularly during large public gatherings that include travelers from many areas.