June 16 (UPI) -- A single dose of one of the two-shot COVID-19 vaccines prevented an estimated 95% of new infections among healthcare workers two weeks after receiving the jab, a study published Wednesday by JAMA Network Open found. The first dose of the Moderna vaccine was 78% effective at preventing new cases just one week after clinical staff were inoculated, the data showed. Still, 39, or just over 1%, of the nearly 3,400 health workers who received the vaccine later became infected with the virus, said researchers, from the VA Boston Healthcare System. These "breakthrough" infections occurred at least...