Methodology

Definitions

Herd Immunity: A population's protection from the spread of an infectius disease caused by a sufficient percentage of the population having immunity to that disease. Learn moreHerd Immunity Threshold: The percentage of a given population required to have immunity to an infectious disease before herd immunity is reached for that population.Herd Immunity Threshold for Covid-19: Infectious disease experts estimate that immunity to Covid-19 in 70-85% of a population would be sufficient for reaching herd immunity.Percentage of population receiving the vaccine daily: Average Doses Administered Daily as a Percentage of Population = (7-Day Moving Average of Daily Doses Delivered / Population) * 100Percentage of Population Vaccinated: Percent Vaccinated = (Total Vaccine Doses Administered * 0.5) / PopulationDays to Herd Immunity: Days = [(Population * 0.7) - (Vaccine Doses Delivered * 0.5)] / (Average Daily Vaccine Doses Given * 0.5)

Assumptions

Herd Immunity for Covid-19: We assume it is possible for a population to reach a state of herd immunnity for Covid-19 through vaccinations.Herd Immunity Threshold for Covid-19: We assume immunity from vaccination in a given 70% of the population is the minimum possible to reach herd immunity. We provide the ability to toggle this threshold up to 95% to account for variations in R values for variants of Covid-19 and varying estimates by infectious disease experts. Learn moreVaccine Dosage: We assume each vaccine is a two-dose vaccine.Vaccination Dosage numbers published per country: We assume each vaccine dose administered equals one person is immune. We then account for the fact that each person requires two doses of the vaccine for immunity by multiplying the total doses delivered to date by 0.5.Immunity from Covid-19 Infection: We do not include confirmed Covid-19 cases in our projection of time to herd immunity. While new studies (as of January, 2020) suggest infection with COVID-19 leads to immunity, the vaccine data does not state whether the person vaccinated was previsouly infected. Additionally, the CDC recommends vaccinations even for those who were confirmed to have been infected with Covid-19 in the past. For these reasons, we've decided to focus on the time for a population to reach herd immunity through vaccination.

Project Code

Github repo for timetoherd.com: https://github.com/pgriggs/timetoherd.com