In the scientific community, there are conflicting definitions for when herd immunity is achieved. Is it when enough people are protected that it begins to have a measurable effect on the speed of transmission? That could begin well before 75% of people are fully vaccinated. Others define it as the point when outbreaks can no longer be sustained. For example, even if there’s a cluster of measles cases in an unvaccinated community, herd immunity prevents it from rippling across a country.
How We Run The Numbers
The vaccines available today require two doses for full vaccination. Our calculations for coverage are based on two doses per person in the population but don't distinguish between first doses or second doses administered. Those breakdowns can distort daily vaccination rates and aren’t available in more than 20% of the countries we’re tracking.
A new vaccine by Johnson & Johnson recently showed positive results using a single dose in a large clinical trial. If approved, we’ll adjust the number of doses required proportionate to its market share in each country.
The vaccines haven’t been authorized for use in children—those studies are currently underway. Our calculator, like the virus, includes children in the population needed to be protected.
One metric Bloomberg’s calculator doesn’t account for is any level of natural immunity that might result from recovering from Covid-19. It’s possible that hard-hit places might require a lower level of vaccination to prevent widespread transmission. While there’s evidence that people who recover from illness do retain some level of natural defenses, it’s unclear how much protection is offered or how long it might last. The vaccine is still recommended for people who have recovered from illness.
The calculator is the latest feature from Bloomberg’s Covid-19 Tracker. The projections are updated daily and are based on the average daily vaccinations in data gathered from 67 countries and the U.S. states and territories. Countries may be excluded when they are in the earliest stages of vaccinations or if they provide infrequent updates on their vaccination numbers.
This article was provided by Bloomberg News.