A spokesman for Walgreens said they believe the outage was caused by a flow of people trying to schedule an appointment, crashing the server.
“We are committed to a perfect scheduling experience to achieve the common goal of vaccinating our most vulnerable populations as quickly as possible,” said the spokesman.
The shutdown comes as US pharmacies, such as Walgreens and CVS, are preparing for a million additional doses of the vaccine promised by the White House last week.
So far, more than 32 million Americans have received at least one dose of the COVID-19 vaccine.
Walgreens told ABC News that as of Tuesday, they will start accepting vaccine appointments as early as Friday, prioritizing healthcare professionals, people over 65 and people with pre-existing illnesses.
ABC News contributed to this report
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