The vaccine rollout in the United States, the nation hardest hit by COVID-19, has gotten off to a choppy start leaving many Americans wondering when they will experience some return to normality.
The World Health Organization estimates “herd immunity” — the share of the population that needs to be immune in order to break the chain of transmission — to be around 60% to 70%. Recently, Dr. Anthony Fauci, the leading infectious disease specialist in the United States, said he thinks the threshold is 75% or higher.
Play with the simulation below to estimate when we could achieve herd immunity and then see how that compares with the current rollout. For simplicity, assume that a two-dose vaccine is administered and that everyone will be vaccinated.
Simulation versus reality
This simulation offers a best guess about when the country could reach herd immunity or full vaccination. There are many assumptions and factors at play that could greatly alter the trajectory.
There’s already some level of immunity. People who were infected with the virus and survived may have some level of immunity. Due to inadequate testing and the asymptomatic nature of this coronavirus, it’s unknown how many people may have immunity or exactly how long it lasts.
The target population size is smaller. The vaccines distributed in the United States are not currently approved for children. And some people may choose not to be vaccinated or wish to wait until later.
States have created their own vaccination plans. Some states lag behind with just a third or 40% of their vaccine allotments being administered. Other states have struggled as eligible patients navigate how to schedule appointments.
The supply of vaccines is expected to increase. The U.S. government has announced the purchase of additional doses that will be delivered by the summer. Also, other vaccines may be approved that require one dose rather than two.
Vaccination rates have increased in early 2021 to a level that makes the incoming Biden administration’s goal of 100 million doses in 100 days achievable. In fact, President Joe Biden has said that he hopes the U.S. will reach 1.5 million doses of vaccine per day.
Fauci said last week that the United States was still in a “very serious situation” with the virus, but that seven-day averages suggested the infection rates were plateauing.
If 70% to 80% of Americans are vaccinated by the end of summer, he added, the country could experience “a degree of normality” by the fall.