This study is similar to many others that have showed that people with prior infection have a much better antibody response to vaccination than do those with no prior exposure to the virus.
The thing that this study adds is that they checked antibodies again two months after the second dose. They found that those with prior infection had less of a decline in that time than those with no prior exposure. Four of the people with prior covid decided to take only one vaccine dose, and their antibody levels over this time were no different from those who took both shots.
This provides further evidence that people with prior covid need only one dose of vaccine. It also suggests that people with prior covid plus vaccination will have protective levels for some time to come.
63 healthcare workers with and without prior Covid infection had their antibody levels compared before and after vaccination with Pfizer's vaccine.
The 33 healthcare workers with prior Covid infection were on average 303 days post Covid diagnosis. They had a mixture of disease severity. 5 were asymptomatic, 22 with mild symptoms, 6 with pneumonia, and 1 that was hospitalized and needed oxygen.
At baseline before vaccination, 4 of the 33 with prior Covid infection were seronegative. However all those with prior Covid had a strong antibody response from the vaccine after one dose. There were no significant differences in antibody response after vaccination between those with prior Covid infection.
Interestingly this study tested antibody levels two months after the second dose of the vaccine in both groups. Antibody levels declined less for those with prior Covid infection.