The Biden Administration’s ambitious plan to vaccinate 300 million Americans by the end of the summer faces multiple challenges — and not all of them are related to distribution or production.

According to a recent survey conducted by the U.S. Census Bureau, 26,590,000 Americans — or 10.7% of the 18 and older population — say they will either probably or definitely not agree to receive the vaccination when given the opportunity.

The share of eligible residents who will likely refuse vaccination varies considerably nationwide, from as many as 25.8% of the adult population to as little as 3.9%, depending on the state. States where the largest shares of adults are open to taking the vaccine are concentrated in the Northeast.

The majority of Americans who have yet to be vaccinated cite one of three reasons: either they are concerned about possible side effects, or they want to wait to see if it is safe, or they think that others would benefit more than themselves from a vaccination. Others cite different reasons.

Nationwide, 15,800,000 people, 6.3% of the adult population, do not trust the COVID-19 vaccines, and 5,780,000, or 2.3%, do not trust vaccines in general. Additionally, 13,630,000 American adults, or 5.5% of the 18 and older population, have not been vaccinated because they do not trust the government.

Meanwhile, the virus continues to spread. Since the beginning of the pandemic, there have been 33,163,632 confirmed cases of the virus and a total of 595,256 Americans have died as a result.

So far, 147,758,585 Americans — or 45.2% of the total population — have received the full course of vaccinations necessary to protect against COVID-19.

All survey data used in this story was published by the Census on June 16, 2021. All data related to COVID-19 infections, fatalities, and vaccinations is current as of June 17, 2021.