Conventional wisdom says that if you’re vaccinated and you get a breakthrough infection with the coronavirus, you can transmit that infection to someone else and make that person sick.
But new evidence suggests that even though that may happen on occasion, breakthrough infections might not represent the threat to others that scientists originally thought.
Ross Kedl, an immunologist at the University of Colorado School of Medicine, will point out to anyone who cares to listen that basic immunology suggests the virus of a vaccinated person who gets infected will be different from the virus of an infected unvaccinated person.
That’s because vaccinated people have already made antibodies to the coronavirus. Even if those antibodies don’t prevent infection, they still “should be coating that virus with antibody and therefore helping prevent excessive downstream transmission,” Kedl says. And a virus coated with antibodies won’t be as infectious as a virus not coated in antibodies.
Not enough evidence
In Provincetown, Mass., this summer, a lot of vaccinated people got infected with the coronavirus, leading many to assume that this was an example of vaccinated people with breakthrough infections giving their infection to other vaccinated people.
Kedl isn’t convinced.
“In all these cases where you have these big breakthrough infections, there’s always unvaccinated people in the room,” he says.
In a recent Israeli study of breakthrough infections among health care workers, the researchers report that in “all 37 case patients for whom data were available regarding the source of infection, the suspected source was an unvaccinated person.”
It’s hard to prove that an infected vaccinated person actually was responsible for transmitting their infection to someone else.
“I have seen no one report actually trying to trace whether or not the people who were vaccinated who got infected are downstream — and certainly only could be downstream — of another vaccinated person,” Kedl says.
There’s new laboratory evidence supporting Kedl’s supposition. Initially, most vaccine experts predicted that mRNA vaccines like the ones made by Pfizer and Moderna that are injected into someone’s arm muscle would generate only the kinds of antibodies that circulate throughout the body.
But that might not be the whole story.
“I think what was the big surprise here is that the mRNA vaccines are going beyond that,” says Michal Caspi Tal, until recently an instructor at Stanford University’s Institute for Stem Cell Biology and Regenerative Medicine and now a visiting scientist at the Massachusetts Institute of Technology.
What Tal has found is that in addition to the circulating antibodies, there was a surprisingly large amount of antibodies in mucosal membranes in the nose and mouth, two of the primary entry points for the coronavirus.