Those methods of tracking vaccine effectiveness aren’t new, even if the virus is. Scientists study post-introduction vaccine effectiveness for every new vaccine that comes out, said Dr. Katherine Fleming-Dutra, a member of the Vaccine Effectiveness & Evaluation Team in the CDC’s COVID-19 Response. And that research has proven crucial to disease prevention.

For example, as part of an effort to eradicate measles in the U.S., scientists began tracking the decades-old measles vaccine in the 1980s. The studies taught them that one dose of this vaccine wasn’t cutting it, according to Dr. Walter Orenstein, professor and associate director of the Emory Vaccine Center at Emory University. In 1989 the CDC and the American Academy of Pediatrics began recommending that everyone get two doses. If you weren’t looking closely, it would have been easy to miss that a second dose was necessary. The first dose of measles vaccine is 93 percent effective. But the disease spreads so easily and rapidly that 93 percent wasn’t quite good enough, Orenstein said. With the second dose, the vaccine becomes 97 percent effective at preventing measles.

The flu vaccine, meanwhile, goes through this process every year. That’s why there’s that network of research centers for the CDC to use to study COVID-19. That system turns out results on flu vaccine effectiveness twice a year, and preliminary results are able to be put together with as little as a month or two of data. But that doesn’t mean we’ll have results as quickly on the COVID-19 vaccines. As the entire public health system has taken great pains to explain this past year, the flu and COVID-19 are not the same beast — and no one I spoke to was willing to estimate how long the results for COVID-19 will take.