Diphtheria has an incubation period of 2 to 5 days, with a range of 1 to 10 days. Almost every mucosal membrane can be affected by disease. Organisms can be found in discharges and lesions of untreated persons for 2 to 6 weeks following infection. The throat is the most common site of involvement; however, any part of the respiratory system may be affected. The virus that causes diphtheria infects cells that line your lungs, nose, mouth, and gut. It takes about 24 hours for the virus to show up in a sample of blood taken from someone with diphtheria. After that, the virus lies dormant in some parts of the body for an average of 10 days before it wakes up again and spreads more easily. This second phase of the illness is when people start feeling sick. There are two phases to this illness: a mild fever and sore throat, followed by a severe form without either fever or soreness. The severity of symptoms will depend on how many bacteria are present at the time of infection. The best defense against diphtheria is a vaccine. A series of shots over several months protects you from the disease. People who have not been immunized may still get sick from diphtheria, but their symptoms will be much worse if they catch the disease from someone who has not been vaccinated. That's why it's important to make sure children get vaccinated.