The team behind the ChAdOx-1 vaccine have said that similar vaccines they worked on in the past (SARS1, MERS) triggered the immune system in a different way tha

The team behind the ChAdOx-1 vaccine have said that similar vaccines they worked on in the past (SARS1, MERS) triggered the immune system in a different way than getting the virus itself and it's expected that the vaccine-derived immune response would last longer than natural immunity. They have re-tested people they immunized for SARS1 and they still showed immune responses over a decade later. So the idea is that the vaccine would still be potentially useful to those who have already had the disease.