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Traditional wisdom says that if you are vaccinated and you get a breakthrough infection with the coronavirus, you can pass that infection on to another person and make that person sick.
However, new evidence suggests that breakthrough infections may not pose the threat to others that scientists originally thought, although it can occasionally do so.
Ross Kedli, an immunologist at the University of Colorado School of Medicine, will point out to anyone who wishes to listen that basic immunology suggests that the virus of a vaccinated person who becomes infected is different from the virus of an infected, unvaccinated person.
Because vaccinated people have already formed antibodies against the coronavirus. Even if these antibodies do not prevent infection, they should still “envelop the virus in antibodies and thus help prevent excessive downward transmission,” says Kedl. And an antibody-coated virus is not as contagious as a non-antibody-coated virus.
Little evidence of easy breakthrough infection transmission
In Provincetown, Massachusetts, many vaccinated people contracted the coronavirus this summer, leading many to believe that this was an example of vaccinated people with breakthrough infections who passed their infection on to other vaccinated people.
Kedl is not convinced.
“In all of these cases where you have these big breakthrough infections, there are always unvaccinated people in the room,” he says.
In one Recent study from Israel on breakthrough infections among healthcare workers, researchers report that “for all 37 patients for whom data on the source of infection were available, the suspected source was an unvaccinated person.”
It is difficult to prove that an infected vaccinated person was actually responsible for transmitting their infection to another person.
“I have not seen anyone who actually tried to find out whether the vaccinated people who became infected are downstream – and certainly could only be downstream – of another vaccinated person,” says Kedl.
There is new laboratory evidence to support Kedl’s suspicion. Initially, most vaccine experts predicted that mRNA vaccines like those from Pfizer and Moderna, injected into someone’s arm muscle, would only produce the types of antibodies that circulate throughout the body.
But that may not be the whole story.
“I think the big surprise here was that the mRNA vaccines go beyond that,” says Michal Caspi Valley, until recently lecturer at the Institute of Stem Cell Biology and Regenerative Medicine at Stanford University and now visiting scholar at the Massachusetts Institute of Technology.
What a valley has found is that, in addition to the circulating antibodies, there were surprisingly many antibodies in the mucous membranes of the nose and mouth, two of the primary entry points for the coronavirus.
The vaccinated are not “sitting ducks”
“This is the first example where we can show that a local mucosal immune response is triggered even though the person received the vaccine intramuscularly,” says Gommerman.
If there were antibodies in the mucous membranes, they would likely coat any virus that got into the nose or throat. Therefore, any virus exhaled through sneezing or coughing would likely be less contagious.
Gommerman says that so far it seemed likely that a vaccine given directly into the mucosal tissue was the only way to make antibodies in the nose or throat.
“Of course, a mucosal vaccination would also be great. But at least we’re not sitting on the pole, ”says Gommerman. “Otherwise everyone would get a breakthrough infection.”
Now these studies are yet to be peer-reviewed by Gommerman and Tal, and some have already indicated that the antibodies they describe may not confer true mucosal immunity.
But there is other evidence that a vaccinated person’s breakthrough infection may not be transmitted efficiently to others.
Marion Pepper, an immunologist at the University of Washington, says a recently published Study from the Netherlands in the laboratory examines how well viruses from vaccinated people can infect cells.
Pepper says the answer wasn’t good.
“If you actually isolate the virus from people who get a secondary infection after vaccination, that virus is less good at infecting cells,” says Pepper. “It’s not known why. Is it covered with an antibody? Maybe. Has it been hit by some other type of immune mediator, cytokine, etc.? Maybe. Nobody really knows a vaccinated person.”
There are other studies that suggest that the virus that a vaccinated person emits is something else that may help prevent transmission.
Whatever it is, Kedl at the University of Colorado says it’s another reason why vaccination is a good idea.
“Because you are even better protected yourself. And you will be better off protecting other people.”
Kedl says you call this a win-win situation.
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