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Many countries are counting on vaccines to build sufficient immunity in their populations so that SARS-CoV-2, the virus that causes Covid-19, isn't able to find enough people to infect, causing transmission to eventually stop. But even in countries with a high proportion of people inoculated with highly effective vaccines, it's unclear whether it's possible to reach the so-called herd immunity threshold anytime soon. Researchers warn that the virus is apt to be circulating among us for a long time, although it's likely to become a less potent foe.

No. So far, only one human disease -- smallpox -- has been officially eradicated; that is, reduced to zero cases and kept there long-term without continual countermeasures. That was thanks to a good vaccine plus the fact that humans are the only mammals naturally susceptible to infection with the smallpox virus. By contrast, many species are susceptible to SARS-CoV-2, including bats, minks, cats and gorillas. The next best thing would be what's known as disease elimination. That's when there are zero new cases in a defined area over a sustained period, such as 28 days. Some countries, such as New Zealand, have achieved zero new cases for lengthy periods using lockdowns, diligent case detection and isolation, and border closures. But keeping this up over the long run is challenging as the emergence of more-infectious variants leads to even stricter public health and social measures, while people hunger for a return to normal life.