Is it obligatory to say "Yarhamuk Allah" to the sneezer after each consecutive sneeze, or after he has finished all repeated sneezes?

Saying "Yarhamuk Allah" (may Allah have mercy on you) to one who sneezes is a communal obligation (fard kifaya) if they praise Allah. The obligation is fulfilled if one person says it to them; otherwise, all are sinful. If sneezing repeats more than three times, one should not say "Yarhamuk Allah" but rather supplicate for their well-being, based on the Prophet's (peace be upon him) saying: "The sneezer is responded to with 'Yarhamuk Allah' for three times; anything more than that, then he is suffering from a cold." When sneezing repeats after the third time, one should say, "May Allah grant you well-being (Afaak Allah)," while explaining the reason: "You are suffering from a cold," so that it is not misunderstood that the supplication for well-being is for something other than a cold.