HealthDay News — The delta variant of SARS-CoV-2 accounts for most cases of breakthrough infection among vaccinated individuals, according to research published in the July 30 early-release issue of the US Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Catherine M. Brown, DVM, from the Massachusetts Department of Public Health in Boston, and colleagues describe an outbreak of 469 cases of COVID-19 associated with events and large public gatherings in a town in Barnstable County, Massachusetts. Among eligible Massachusetts residents, vaccination coverage was 69%.

The researchers found that 74% of the cases occurred in fully vaccinated individuals. The B.1.617.2 (delta) variant of SARS-CoV-2 was identified in 89% of the 133 patients who underwent genomic sequencing; the delta AY.3 sublineage was identified in one patient. Of the vaccinated patients with breakthrough infection, 79% were symptomatic. Five patients were hospitalized, 4 of whom were fully vaccinated; there were no deaths. Real-time reverse transcription-polymerase chain reaction cycle threshold values were similar in specimens from 127 vaccinated persons with breakthrough cases and in 84 persons who were unvaccinated, who were not fully vaccinated, or whose vaccination status was unknown.

“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,” the authors write.


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