Path to Herd Immunity Normality : 2021 Outlook of COVID-19 in the US

By: Youyang Gu
Last Updated: April 26, 2021 (Model last updated: March 5, 2021; First posted December 9, 2020)

Note: Our last model update was in March 2021. We are no longer updating this page. Read more from Youyang here.

With the availability of the COVID-19 vaccine, we present our best estimate of the path to COVID-19 herd immunity / normality in the United States. Immunity against the SARS-CoV-2 virus comes from two sources: vaccination and natural infection. On this page, we provide the latest COVID-19 vaccine projections and current vaccination progress.

June 24, 2021 Note: See our new COVID-19 Population Immunity Calculator. This calculator estimates the true proportion of a population that have immunity against COVID-19, factoring both immunity from vaccination and natural infection. This is the basis for the computation of total immunity in this model.

April 26, 2021 Update: Scroll down or click here to see a comparison of our last projections from March 5 to what actually happened.

April 21, 2021 Note: We uploaded historical daily CDC vaccination data here. It contains the raw data released by the CDC on each date. This has no look-ahead bias, so it is especially useful for training models.

April 13, 2021 Note: Recent delays such as the halting of the Johnson & Johnson vaccine and the ruining of 15 million J&J doses in March mean that actual vaccinations may slightly lag our final projections. On the positive end, the general adult population in all 50 states will be able to receive the vaccine by the end of April, matching our projections from January.

March 8, 2021 Update: We have ended our daily updates for and hence are no longer be updating this page. Read Youyang’s One Year Later blog post for a detailed explanation and for a list of alternate resources. You can view the latest vaccination trends on the CDC website. Thank you for your support over the past year.

February 24, 2021 Update: See our latest thoughts on when to expect a return to normal.

February 11, 2021 Update: We changed the page title from “Path to Herd Immunity” to “Path to Normality”. Our modeling suggests that it is increasingly unlikely that we will reach theoretical herd immunity in 2021. See our Feb 11 thread on why the recent attention to herd immunity is overblown, and why we should shift our focus away towards normality instead.

Older updates

Last updated - Path to Normality plots: Fri, Mar 5 2021 3am ET

Note: Our infections estimates include all new infected individuals of the SARS-CoV-2 virus, not just those that took a COVID-19 test and tested positive. As of January 2021, we estimate the true number of infected individuals in the US to be roughly 2-4x higher than the reported cases (25-50% detection rate). See our writeup, Estimating True Infections, for a more detailed look into this subject.

Note #2: We stopped updating CDC vaccination data on March 8, 2021. For the latest time series, visit the CDC website or our GitHub. See our old plots through March 8 here.

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Comparison: Projected vs Actual

Below is a comparison of our last vaccination projection on March 5, 2021 with what happened since. Our vaccination numbers come from the CDC. You can download our final vaccinations projections here. We initially also included a comparison of true infections, but due to the rise of the Delta variant, our original methodology for estimating true infections by applying a prevalence ratio is no longer applicable.

Comparison last updated: Wed, Jan 26 2022 1am ET

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Public health messaging should be clear and consistent

As the below example shows, this has not always been the case:

When can we return to normal

We define “normality” as the removal of all restrictions for the majority of US states.

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Table of Contents

Note: All of the projections, results and assumptions below have not been changed since March 8, 2021.

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Relevant Twitter Threads

See our Twitter Threads page.

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We use vaccination data from the Centers for Disease Control and Prevention (CDC). We upload the raw and adjusted CDC vaccination time series datafor download on GitHub. It contains daily CDC vaccination updates since they started releasing data on Dec 20, 2020.

While we release daily past infections estimates for every state and county, we are currently not releasing our vaccination and infections forecasts. This is due to 1) the limitations and noisiness in the existing data 2) the high degree of uncertainty for the future and 3) the reliance on numerous assumptions (outlined below). As a result, we believe these projections are best suited to be viewed in the context of everything outlined on this page, and should best not be used independently. Without all the necessary context/assumptions, the results can easily be misinterpreted.

You can download our final vaccinations projections from March 5, 2021 here.

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The underlying assumptions behind our estimates are presented below:

Basic Assumptions

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Vaccination Assumptions

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Infection Assumptions

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Helpful Data Sources

Below you will find a list of helpful vaccination data sources and dashboards. While we do not directly use them in our modeling, we highly recommend giving them a look.

Vaccine Rollout Tracker

Vaccine Development Tracker

Questions? Comments? Feedback?

You can reach Youyang Gu via the Contact page.

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Past Updates