In the last few [winter] months, schools all over the country have closed because of outbreaks of norovirus. Also known as stomach flu, norovirus infections cause watery diarrhea, low-grade fever and, most alarming of all, projectile vomiting, which is an extremely effective way of spreading the virus.
Norovirus is very infectious and spreads rapidly through a confined population, such as at a school or on a cruise ship. Although most sufferers recover in 24 to 48 hours, norovirus is a leading cause of childhood illness and, in developing countries, results in about 50,000 child deaths each year.
Interestingly, not everyone is equally vulnerable to the virus, and whether you get sick or not may depend on your blood type.