This is a double -blind, placebo controlled study in which the investigational drug and the reference placebo group are gargled and swallowed. 70 ml IgY/ placebo solution is gargled every night for two minutes (for maximal 24 months) The design will include the recruitment of 144 patients randomized in two groups (72 per treatment group) In order to compensate for dropouts (i.e. patients dropping out prior to 24 months without having an event) the total sample size was planned to be approximately 180 (i.e. ~20 % dropout rate). After the actual drop-out rate has been low throughout the study, only 144 plus approx. 10% potential drop-outs were included into the study.