There are 2 reasons for JNJ’s lower top line numbers.

1) There were more of the variants going around, not more of the original strain going around when JNJ was tested and all the vaccines are less effective against the variants. PFE and MRNA were tested when only the original strain was going around. All the vaccines were designed to combat the original strain.

2) JNJ doesn’t protect as well against mild Covid. But the symptoms from this mild Covid are comparable to the side effects from the second dose of PFE/MRNA which affect 30-40% of people and based on anecdata from people I know nearly everyone.