The US Centers for Disease Control and Prevention says it has administered over a million doses of COVID-19 vaccines as of Wednesday.
The CDC also says they have distributed more than 9.46 million doses across the country.
Priority is currently being given to healthcare workers and elderly care home residents in the early phase of the vaccination program across the country. A private research institute says the number of people in these groups is over 17 million.
The CDC plans to expand the scope of the vaccination program in phases. Next in line for the vaccine will include police officers, firefighters, people aged 75 and older, teachers and grocery workers.
Meanwhile, the CDC says it received a report that six people who were given the shot developed severe allergic reactions.
Officials with the CDC and the US Food and Drug Administration are investigating the cases. The officials have issued guidelines for safe vaccinations. They called for a system under which recipients are observed after vaccination and treated immediately in case of any adverse reaction.
US Health and Human Services Secretary Alex Azar has said he expects a total of 100 million doses of the Pfizer and Moderna vaccines to be distributed by the end of February.
He added more doses should be available if Johnson & Johnson and the AstraZeneca vaccines are approved.