5. Pneumococcal Disease What it is: A bacterial disease that can cause many types of illness, including pneumonia, ear and blood infections, and meningitis (which affects the brain and spinal cord). How you get it: By coming into contact with an infected person’s mucus or saliva. Why it’s serious: Complications can be serious and fatal. As pneumonia, it's especially deadly in people older than 65. If it causes meningitis or infects the blood, these can be life-threatening.