When will the pandemic end? It's the question hanging over just about everything since Covid-19 took over the world last year. The answer can be measured in vaccinations.
Bloomberg has built the biggest database of Covid-19 shots given around the world, with more than 119 million doses administered worldwide.
US experts like Dr Anthony Fauci have suggested it will take 70 per cent to 85 per cent coverage of the population for things to return to normal.
Some countries are making far more rapid progress than others, using 75 per cent coverage with a two-dose vaccine as a target.
With vaccine manufacturers scaling up production, more people will be vaccinated in a shorter time.
With vaccinations happening more rapidly in richer Western countries than the rest of the globe, it will take the world as a whole seven years at the current pace.
Bloomberg's calculator provides a snapshot in time, designed to put today's vaccination rates into perspective. It uses the most recent rolling average of vaccinations, which means that as vaccination numbers pick up, the time needed to hit the 75 per cent threshold will fall. The calculations will be volatile, especially in the early days of the roll-out, and the numbers can be distorted by temporary disruptions.
More than 8.5 billion doses of vaccine have been contracted by countries through more than 100 agreements tracked by Bloomberg. Only a third of countries have even begun their vaccination campaigns.
Vaccinations protect people against Covid-19 within a few weeks of getting the shots. But if just a few people in a community get vaccinated, the virus can continue to spread unchecked.
As more people get the vaccine, groups of people start to build a collective defence against the virus so that isolated sparks of infection burn out instead of spreading into an outbreak.
The concept is known as herd immunity. 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 per cent 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.
