There are two people on an island: Ross and Tony. Ross gets utility from vaccination from disease X, vR, and from consumption, cR, as follows: uR(cR, vR) = Rln(vR) ln(cR). For some rare reason, the vaccine does not work for Tony. His utility, however, does depend on vR, because he positively evaluates the fact that Ross is less likely to infect him with disease X. That is, uT (cT , vR) = T ln(vR) ln(cT ), where T < R. The (exogenous) price of the consumption good is pc = 1 and the (exogenous) price of the vaccine is pv = 1. The incomes of Ross and Tony are IR and IT , respectively