How effectively do newborns fight off colds and flus?

Some good, some bad: Simple colds newborns usually have fairly good resistance to through antibodies the mother has in her system. True influenza, though, varies a lot. If the mother received an influenza vaccine during the pregnancy, there are protective antibodies the baby has received that help a lot. But if mom is not vaccinated for that year, newborns are at great risk for influenza and can become very ill.