To build a scalable interactive voice response (IVR) system using Twilio, AWS, and Python Flask, start by setting up a Twilio phone number and an S3 bucket on AWS with public access enabled. Create a TwiML Bin that defines the decision tree for your IVR, including audio files and callback URLs. Next, build a Python Flask application to handle user input and interact with the TwiML Bin. Use the Flask app to route incoming calls based on user input, such as COVID-related symptoms or non-COVID emergencies. Deploy the application to AWS Elastic Beanstalk, configure the instance settings, and update the Twilio phone number configuration to use the new IVR system. With this setup, you can create a cloud-based IVR that helps emergency call centers manage calls more efficiently during crisis situations.