Can COVID vaccines stop transmission? Scientists race to find answers
As countries roll out vaccines that prevent COVID-19, studies are under way to determine whether shots can also stop people from getting infected and passing on the SARS-CoV-2 virus. Vaccines that prevent transmission could help to bring the pandemic under control if they are given to enough people.
Preliminary analyses suggest that at least some vaccines are likely to have a transmission-blocking effect. But confirming that effect — and how strong it will be — is tricky because a drop in infections in a given region might be explained by other factors, such as lockdowns and behaviour changes. Not only that, the virus can spread from asymptomatic carriers, which makes it hard to detect those infections.
“These are among the hardest types of studies to do,” says Marc Lipsitch, an infectious-disease epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts. “All of us are out there, hungrily trying to see what we can get out of little bits of data that do come out,” he says. Results from some studies are expected in the next few weeks.