As the novel coronavirus continues to spread across the globe, variants of the virus also continue to emerge. Many of these new variants are more contagious than their predecessors and have added a new urgency to vaccine distribution.

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, 44,970,000 Americans — or 18.0% 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 32.8% of the adult population to as little as 8.4%, 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 are against personally taking the vaccine 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, 19,860,000 people, 8.0% of the eligible population, do not trust the COVID-19 vaccines, and another 8,530,000, or 3.4%, do not trust vaccines in general. Additionally, 17,660,000 American adults, 7.1% of those eligible, will likely refuse a vaccination because they do not trust the government.

Meanwhile, the virus continues to spread. In the last week alone, another 496,320 Americans tested positive for the virus and 14,266 have died. Since the beginning of the pandemic, there have been 28,264,994 confirmed cases of the virus and a total of 497,759 Americans have died as a result.

So far, only 25,466,405 Americans — or 10.2% 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 Feb. 24, 2021. All data related to COVID-19 infections, fatalities, and vaccinations is current as of Feb. 28, 2021.