Twist: use the previous victim as a recipient for the payment.

This would create an interesting spread incentive for the attack: once you are infected and you pay, you can still be reimbursed if you manage to infect someone else. You could even make this into a pyramid where several person's payment go to a parent carrier, and people will even want to be infected quickly to be closer to the top of the pyramid.

Or just use a random previous victim id. Now it becomes a viral non-consensual lottery and you benefit from spreading it.