Reference:
Chau, N. V. V., Ngoc, N. M., Nguyet, L. A., Quang, V. M., Ny, N. T. H., Khoa, D. B., Phong, N. T., Toan, L. M., Dung, N. T., Yen, L. M., Thwaites, G., & Tan, L. V. (2021). An observational study of breakthrough SARS-CoV-2 Delta variant infections among vaccinated healthcare workers in Vietnam. EClinicalMedicine, 41, 101143. https://doi.org/10.1016/j.eclinm.2021.101143
Summary:
This observational study investigated breakthrough infections of the SARS-CoV-2 Delta variant among vaccinated healthcare workers at a hospital in Ho Chi Minh City, Vietnam. Conducted between 11th and 25th June 2021, the study involved 62 staff members who tested positive for the virus, with most experiencing asymptomatic or mild symptoms. Notably, these cases exhibited high viral loads—over 250 times higher than those infected with the original strain—and prolonged PCR positivity, lasting up to 33 days. The study also highlighted that neutralising antibody levels in infected individuals were significantly lower compared to uninfected, fully vaccinated controls, although no correlation was found between antibody levels and viral loads. Whole-genome sequencing confirmed that all cases were of the Delta variant, which was phylogenetically distinct from other circulating strains. The findings suggest that even fully vaccinated individuals can transmit the virus, underscoring the need for continued public health measures, including social distancing and ventilation improvements, to mitigate transmission risks.