Only a handful of vaccines generate lifetime immunity for most people, such as the ones for measles, a viral infection that naturally produces lifelong immunity. Experts caution against expectations of such longevity for Covid-19, citing experience with other respiratory viruses plus emerging data on the longevity of the antibodies that can prevent the virus from entering human cells and replicating.
To fill in knowledge gaps on vaccine duration, researchers and vaccine developers are looking closely at emerging science of immune responses in recovered patients, and how that science can be applied to vaccine development.
The first Covid-19 vaccine study is expected to be completed in the fall, but scientists don’t have the luxury to wait until the science is settled, or at least better understood. An emergency authorization by regulators could come before duration is known. Trials are progressing as natural-immunity studies are rapidly pouring in from labs onto online servers and the pages of scientific journals.
Francis Collins, director of the National Institutes of Health, said it would be hard to know whether a Covid-19 vaccine protects for a year after testing it for only a few months, but he said recovered patients who don’t become reinfected after a year “would be a good sign that the vaccine ought to work” for at least that long.
