And those antibodies protected the vaccinated people if they became infected with a full-blown Ebola virus. This type of vaccine, called a viral vector vaccine, came with a big risk: The recipients might develop immunity to the viral vector after just the first dose. When the second dose arrived, their immune systems could swiftly wipe out the viral vector before it delivered its payload. In 2017, for example, researchers at the Gamaleya Research Institute in Russia created an Ebola vaccine whose first dose contained a virus called an adenovirus. The first dose used the same adenovirus as in their Ebola vaccine, called Ad5.

Source: New York Times March 30, 2021 19:00 UTC