In this study a quanta independent relative risk reduction calculation method was developed and tested in typical model rooms against the quanta method that calculates absolute risk with fixed virus emission. With a lowest possible Category IV ventilation rate used as reference, the results show that relative risk of 0.5 is achieved with reasonable ventilation rates in the classroom and office, but in rooms with higher viral load even higher risk reduction of about 85%, i.e. relative risk of 0.15, might be reasonable level for the target ventilation rate. When applied for design with fixed relative risk value the method provided the lowest ventilation rate per person at highest occupant density that is not logical. This may underestimate the required ventilation rate in rooms with high occupant density. It is concluded that the method should not preferred for ventilation design because the quanta method proposed to EN 16798-1 revision is capable to handle occupant density variations in correct fashion. Relative risk reduction method may be useful for existing buildings because it is possible to calculate the risk reduction from the initial case conditions without any uncertainty related to the viral load. For instance, if sick leave or disease cases data is available for a specific building, it can be calculated how much the ventilation would have been needed to be increased to reduce the number of disease cases to a specified level. It can be also used to refine critical parameters in the quanta method.