Neil Johnson, a physicist at George Washington University who is studying vaccine skepticism on social media, told CNN the four most common objections are: safety; whether a vaccine is needed; trust of the establishment and pharmaceutical companies; and perceived uncertainty in the science.
To see how widespread hesitancy is, he suggests asking your family and friends whether they would take a Covid-19 vaccine if one were available now.
"I would be surprised if you ask 10 people and you get all 10 jumping and saying yes without adding any caveats," he said.