AWS Public Sector Blog

Accelerating COVID-19 vaccine rollout with Zocdoc on AWS

man with face mask getting vaccine from nurse with mask and face shield

With more than 1,400 different systems that healthcare providers use to run their scheduling, and millions of Chicago residents seeking a vaccine, a unified, citywide rollout for COVID-19 vaccinations is a challenge for the city. Like many municipalities, early in the pandemic, the city of Chicago preferred to offer its residents a centralized find-and-book appointment system for COVID-19 testing, but other priorities and operational challenges prevented this.

However, for vaccines, the team leading the city’s COVID-19 vaccination response was determined to deliver a more seamless experience for residents. The city used the Zocdoc Vaccine Scheduler built on Amazon Web Services (AWS).

“For some people, making vaccination more convenient will mean the difference between whether they get vaccinated or not, and we want to bring down every barrier that we can,” said Christina Hildreth Anderson, Chicago’s deputy commissioner and chief of operations for COVID-19 response for the Chicago Department of Public Health, in a recent interview. “We realized that the problems we had with testing would be the same problems we have with vaccinations. In conversations with my team, we said, ‘We need a Zocdoc for vaccines.’ And, it turns out, Zocdoc already had one.”

The Zocdoc solution aggregates and centralizes available appointments from all kinds of vaccine providers, including city, county, state, and federally run sites, as well as private practices and health systems. Instead of asking residents to search for an appointment themselves among multiple disconnected websites, the solution delivers a seamless, unified scheduling experience—regardless of which entity administers the vaccine.

In mid-January, the Zocdoc team began talks with the city, and the solution was live just three weeks after the conversations began. On the first day it was open to the public, the system booked up to 300 vaccination appointments per minute.

Instantaneous aggregation for a real-time availability of appointments

Zocdoc was able to deploy its scheduler in a matter of weeks because of its core technology, Patient-Powered Search™, an intuitive search experience, built specifically to bridge the gap between healthcare industry and human speak. It seamlessly connects to many of the 1,400 different practice management systems (PMS) and electronic health record (EHR) platforms providers use to run their backend calendars for patient visits, then surfaces real-time appointment availability. While Zocdoc prefers to work with open standards like HL7 FHIR, many of these PMS and EHR systems are walled gardens that make interoperability difficult.

“When a scheduling website works well, it looks and feels effortless. But the technology underneath is enormously complicated,” said Oliver Kharraz, chief executive officer (CEO) and founder of Zocdoc. “Building connections between those walled gardens requires years of time and investment, plus constant maintenance. Onboarding providers and health systems is something we’ve been optimizing for the past 13 years, and it’s what prepared us to address this massive need.”

Zocdoc’s integrations make it easier for patients to reach providers across various platforms, see available appointment slots, and book appointments in real time. The integrations are built in-house and can usually be deployed in less than 30 minutes. Zocdoc also has a robust web-based booking management system that can be deployed to sites where there is no existing backend scheduling system, or the provider prefers to run their vaccine scheduling separately. And because the connectors are already built, Zocdoc has even added new sites to the Chicago solution with just a one-day turnaround.

Resiliency at scale for sustained high traffic

Demand for COVID-19 vaccinations is high—so high that the Zocdoc Vaccine Scheduler booked the first batch of available appointments in Chicago before the press conference to announce its launch had concluded. With all that traffic, the ability to scale is paramount.

“The problem of scale adds a whole new set of challenges,” Kharraz said. “It isn’t good enough for a scheduling website to work on a typical day, or even most of the time. The infrastructure has to be tested to ensure that it holds up during huge spikes in demand, when thousands of people are trying to book an appointment at once.”

The Zocdoc team made sure they could scale across the full stack, including searches, availability queries, and booking transactions. The solution relies on built-in, container-based auto-scaling of Amazon Elastic Container Service (Amazon ECS) and uses caching at multiple layers of the application to maintain a fast user experience under the increased load. The Zocdoc team also increased the shard count of Amazon Kinesis Data Streams, which powers the real-time availability function, to make sure it could handle peak traffic.

Power to the patient

To date, Zocdoc has supported peak rates of more than 750 bookings per minute for Chicago residents. Learn how new cities, states, and large partners can start using the Zocdoc Vaccine Scheduler—entirely free of charge to support public health efforts at

Learn more about healthcare on AWS.

Tim Condello

Tim Condello

Tim Condello is a senior solutions architect at Amazon Web Services (AWS).

Eric Zimmerman

Eric Zimmerman

Eric Zimmerman is part of the startup and venture capital business development team at Amazon Web Services (AWS) focusing on healthcare and life sciences. He also works in product management for open source, pre-competitive tools to make conducting science on AWS easier. Prior to AWS, Eric was a venture capitalist investing in biotech and medical device companies.

Obi Obidike

Obi Obidike

Obi Obidike is part of the digital native business team at Amazon Web Services (AWS), managing healthcare and life sciences customers in the northeast US.

Zocdoc Engineering Team

Zocdoc Engineering Team

Zocdoc is a New York City-based online medical appointment booking service that allows people to find and book medical care. Each month, millions of patients use Zocdoc to find in-network neighborhood doctors, instantly book appointments online, see what other real patients have to say, get reminders for upcoming appointments and preventive check-ups, fill out their paperwork online, and more.