FluMist (Influenza Virus Vaccine, Live, Intranasal), the first nasally administered influenza vaccine, is now approved for use in children two to five years old. Formerly, the vaccine was approved for use in children at least five years old, adolescents, and adults as old as 49 years. FluMist now augments Fluzone and Fluvirin as influenza virus vaccines approved for use in young children (Fluzone can be administered to children six months of age or older, and Fluvirin to children four years of age or older). In studies in children six to 59 months old, the most common adverse effects of FluMist were runny nose, nasal congestion, and slight fever. They were generally mild. Wheezing also was noted. The use of FluMist in children under two years isn't indicated because in clinical trials it was shown that they're more likely to develop wheezing necessitating hospitalization. Additionally, because FluMist can also exacerbate wheezing, it shouldn't be taken by anyone with asthma or administered to children younger than five years old who have recurrent wheezing (attributable to reactive airway disease, for example). As many other vaccines are, FluMist is developed in fertilized chicken eggs, and allergy to such eggs or to products containing them is a contraindication to its administration.