Babies in Infant Care prone to falling sick

Hi mommies, I am a FTM and have placed my baby in infant care when he is about 4 to 5 months. I understand that during the initial stage of placing baby in infant care, he will be prone to falling sick. For mummies who also place their babies in infant care, may I know how frequent does your babies fall sick, and how soon will he outgrow this stage?