Question:

I heard someone say that if you get the vaccine, you could still be a carrier and spread the virus even if you didn't notice you were sick. Is that true or just a rumor they picked up?

Answered by infectious diseases expert Sara Bares, MD:

This is a great and important question and the answer has changed since the emergence of the delta variant. Prior to delta, vaccines reduced transmission by about 90% and this was very reassuring. However, new data evaluating breakthrough infections in patients infected with the delta variant demonstrate similar viral loads in vaccinated versus unvaccinated patients. The viral load likely correlates with transmissibility. 

In summary, the virus is changing and we are learning more about the new variants (including the now predominant delta variant) every day, but it is possible for someone who has been vaccinated to develop a breakthrough infection (with or without symptoms) and spread the virus. This is why public health experts recently recommended that vaccinated people resume wearing masks in indoor public spaces and around those who are not vaccinated.