Bloom wanted to find out, so he gathered some blood samples from people who may have been in contact with 229E. The blood samples were decades-old, and they got tested for antibodies, against different versions of the coronavirus. The study goes back up to the 1980s.
The results came in and Bloom found them surprising. Blood samples that were from the 1980s had high levels of antibodies that were responsible for blocking the infection against a 1985 version of 229E. However, they had less capacity to get rid of the 1990s version of the virus. Furthermore, they were even less efficient against 229E variants from the 2000s and 2010s.