Breakthrough infections may be less contagious

Fully vaccinated individuals who get infected with the coronavirus spread the infection to fewer people and are contagious for less time compared to people who are partially vaccinated or unvaccinated, a small study from South Korea suggests.

In 173 hospital workers with COVID-19, including 50 who had breakthrough infections, researchers found that the virus had been transmitted to others in the hospital by 7% of the vaccinated group compared with 26% of the unvaccinated, even though the two groups had similar viral loads when diagnosed.

In a separate group of 45 people with mild COVID-19 who were being quarantined, the researchers observed shedding of infectious virus particles for four days in the six people who had been fully vaccinated, 8 days in the 11 partially vaccinated people, and 10 days in the 28 unvaccinated people. All of the infections were acquired before the Omicron variant was circulating, the researchers noted this week in JAMA Network Open.

“Data from this study provide important evidence that despite the possibility of breakthrough infections, COVID-19 vaccinations remain critically useful for controlling the spread of SARS-CoV-2,” the researchers said.