An infant's immune system does not mature until 2 to 3 months. In those first few months, the immune system is underdeveloped and not equipped to fight off viruses. Take the below steps to reduce your baby's risk of sickness: Limit outside exposures - The first two months are regarded as sacred and you must try to limit outdoor exposures as much as possible. Follow strict rules - Always insist on visitors to wash their hands or use a sanitizer before touching your baby. Watch for fever - Any fever – 100.4 F or higher needs to be discussed with your paediatrician. Keep up with vaccines - Keep your infant up to date with all vaccines.