In a CDC survey conducted in Sep 2020, the most cited reasons for people to not get vaccinated were concerns about side effects and safety of the COVID-19 vaccine, waiting to see if the vaccine is safe and receiving it later, lack of trust in the government, and concern that COVID-19 vaccines were developed too quickly.
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Infographics:
Reasons Why Adults Did Not Get the COVID-19 Vaccine (U.S. Census Bureau, accessed 12/24)
https://www.census.gov/content/dam/Census/library/stories/2021/12/who-are-the-adults-not-vaccinated-against-covid-figure-1.jpg