The FDA has authorized two vaccines to prevent infection by SARS-CoV-2 — the virus that causes COVID-19. The CDC has recommended that the first recipients of the vaccines should be healthcare workers and residents of long-term care facilities.

One goal of a vaccine is herd immunity: inoculating a large enough proportion of susceptible individuals to prevent infections to those who have not been inoculated. Herd immunity depends on many factors, but in large part on the efficacy of the vaccine and the proportion of susceptible individuals who are inoculated. Pfizer has reported their vaccine is potentially 95% efficacious at preventing an infection and Moderna announced a vaccine efficacy of 94.1%. An available vaccine is voluntary and recent reports suggest only about 71% of the population may be willing to be inoculated.

Data sources and more information:

• The COVID-19 ForecastHub
• The CDC’s COVIDView website
• Morbidity and Mortality Weekly Reports
• Data on Hospitalizations and Death by Age
• Data on Hospitalizations and Death by Race/Ethnicity
• The National Center for Health Statistics count of deaths
• CDC’s US COVID19 Cases and Deaths by State over time
• The Atlantic’s COVIDtracking project
• Data from John Hopkins University CSSEE COVID-19 Dataset
• A side-by-side comparison of the Pfizer/BioNTech and Moderna vaccines
• KFF COVID-19 Vaccine Monitor: December 2020

What will be the cumulative number of deaths due to COVID-19 on 2021-12-31 if greater than or equal to 50% of Americans initiate vaccination (1st dose received) with a COVID-19 vaccine by 2021-03-01?

The percent of the population that received a COVID-19 vaccine on or before 2021-03-01 will be computed by dividing the number of individuals who have initiated vaccine (1st dose taken) provided by the CDC COVID data tracker by the current US population which on 2021-01-04 was reported to be 330,782,991 and multiplying this fraction by 100. The CDC COVID data tracker that counts the number of individuals who have initialized vaccination will be accessed when data is available after and as close as possible to 2021-03-01.

To resolve deaths, we will use the cumulative number of deaths due to confirmed COVID-19 as recorded in the Johns Hopkins University (JHU) CSSE Github data repository. This file records the daily number of deaths by county. From this file deaths are summed across all counties and aggregated to week to generate the number of new deaths per week. The report will be accessed one week after 2021-12-31.

9 January edit: This question will resolve ambiguously if less than 50% of Americans are vaccinated by 2021-03-01.