For influenza, close contacts of contagious index cases are entitled to receive antiviral PEP within 48 h after exposure to prevent them from becoming ill and further spreading of the disease. Starting oseltamivir within 48 h does not prevent disease but shortens the disease period, mitigates symptoms and might decrease further transmission. Awareness among contacts to seek medical evaluation when influenza-like (ILI) symptoms occur, for both proper antiviral treatment and (home-) isolation advice, reduces further spreading. As influenza has a relative short latent period, for influenza A(H1N1)/2009 varying between 0,7-3,1 days [16, 17] , contacts ideally should be informed within 1 day. Oseltamivir postexposure prophylaxis for this pandemic strain is reported to be effective even when administrated more than 48 h after exposure in household settings [18] , however, delays in administration are not specified. We cannot exclude the possibility that in our study, even delayed administration of oseltamivir prophylaxis may have prevented some people from becoming ill, although we anticipate the effectiveness of the intervention overall to be less in this setting than in households.