Question: Is anyone studying whether being vaccinated protects you from also carrying the virus? I am worried because pretty soon, a large contingent of adults will be vaccinated but our kids still won’t be. It would be nice to know if vaccinating someone also might confer a reduced risk to the kids in their household or classroom.

Answer: We do not yet know whether being vaccinated also protects you from being infected and contagious (see Q&A of 12/13 and more details below). Yes, studies are underway, but it will be some time before we have the results.  Yesterday, Dr. Lena Wen answered a very similar question for CNN, explaining that “We don’t know if people who are vaccinated could still be carriers of the virus, even if they don’t get sick. That means you could be protected yourself if you get exposed to someone with coronavirus, but you could still be a carrier of the virus. When you get together with your loved ones, you could spread it to those who aren’t vaccinated.”  A related article published earlier today in Quartz concludes, “it’s vital that even after receiving both doses of the Covid-19 vaccine, all individuals wear masks, practice physical distancing, and wash their hands when around those who haven’t been vaccinated—just in case.”  

I was confused as to why the vaccine would be so effective at preventing disease but may not be effective at preventing infection and transmission.  In that vein, I found the aforementioned Quartz article, Can you spread Covid-19 if you get the vaccine?, very informative.  Basically, we know that the currently approved vaccines are really good at eliciting IgG antibodies, which quickly react to foreign invaders.  However, we don’t know whether and how well the vaccines elicit IgA antibodies. IgG antibodies circulate in our blood and muscles and do not interact with the outside world, unlike IgA antibodies, which patrol outward facing mucosal surfaces– like the nose– and prevent foreign invaders from further entering the body.  As I understand it, IgG antibodies go to work once the body is invaded whereas IgA antibodies keep the body from being invaded.  Since we don’t know how the vaccines impact IgA antibody response, we don’t know whether vaccination prevents infection.  Assuming that a vaccinated person can become asymptomatically infected, and since we don’t know how much of the SARS-CoV-2 virus is necessary to cause a new infection, we also don’t know whether vaccination prevents transmission.  In heartening news, Emory University immunologist Matthew Woodruff tells Quartz, ““I can’t imagine how the vaccine would prevent symptomatic infection at the efficacies that [companies] reported and have no impact on transmission.”