Vajranabha is not a bhav (birth) of Mahavira. In Jain tradition, Vajranabha is the 11th bhav of Rishabhanatha (Adinath) in the earlier half of the cosmic cycle. Mahavira, on the other hand, is the 24th Tirthankara in the current descending half-cycle (the present bhav for Jain tradition). So, Vajranabha belongs to a preceding cycle, not to Mahavira’s bhav.