Among women who are not pregnant or planning to become pregnant nationally, fewer than 60% said they would receive the vaccine, the data showed.
Willingness to receive the vaccine among women across the country was on par with their counterparts in Russia, but lower than rates seen in countries in Latin America, India and the Philippines, the researchers said.
To date, there has been no indication that any of the COVID-19 vaccines approved for use in the United States -- from Pfizer-BioNTech, Moderna and Johnson & Johnson -- are unsafe for pregnant women, although data is limited, according to the Centers for Disease Control and Prevention.
However, pregnant women are at increased risk for serious illness from the virus, the agency said.
"The perceived threat of COVID-19, level of trust in public health agencies, and existing pre-COVID 19 vaccine attitudes play key roles shaping vaccine acceptance and confidence," study co-author Julia Wu said in a statement.
"Vaccination campaigns should be tailored to alleviate these specific concerns," said Wu, principal investigator with the Human Immunomics Initiative at Harvard T.H. Chan School of Public Health in Cambridge, Mass.
The findings are based on an online survey of nearly 18,000 women in 16 countries, who responded to questions about a hypothetical safe and free COVID-19 vaccine with 90% efficacy in November, before any vaccine was approved for use.
Globally, 52% of responding pregnant women and 73% of "non-pregnant" women said they would receive such a vaccine, and 69% of all women surveyed indicated that they would vaccinate their children age 18 and younger.
Vaccine acceptance varied by country, with more than 60% of pregnant women in India, the Philippines and Latin American countries, and just under 80% of non-pregnant women in these countries, saying they would receive the shots.
In addition, more than 75% of mothers in the these countries and regions indicated they would vaccinate their children, according to the researchers.
Fewer than 45% of pregnant women in the United States and Russia, however, said that they would get the vaccine.
And just under 56% of non-pregnant women in these two countries indicated they would get vaccinated.
Similar percentages were also seen in countries with very few COVID-19 cases, such as Australia and New Zealand.
"This phenomenon" in the United States and Russia "could be due to COVID-19 denial," or the belief that the virus is not a severe health problem, the researchers said.
Pregnant women respondents who were reluctant said they had concerns about exposing their developing babies to possible harmful side effects, the vaccine being rushed for political reasons and the lack of safety and effectiveness data in pregnant women.
"Our study confirmed that COVID-19 vaccine hesitancy is multifaceted," Wu said.