Some viral infections increase the risk of developing cancer. Bacteria-infections may also raise the risk of certain cancers. The most widely studied family of cancer-causing viruses are papillomaviruses (HPV, human papilloma virus), some of which contribute to chronic inflammation and eventually Cervical Cancer. [25] In addition, papillomaviruses can cause other cancers, such as pharyngeal cancer. [26] Long-term follow-up studies are underway to determine to what degree HPV vaccines often prevent cancer. [27]

The Helicobacter pylori bacterium raises the risk of gastric cancer. [28] Chronic inflammation of the liver (infections with hepatitis B and C viruses) is associated with increased risk of Liver Cancer. A vaccination program for hepatitis B virus ( HBV), initiated in Taiwan in 1984, led first to a decrease in HBV prevalence, and subsequently to a substantial reduction in the incidence of Liver Cancer in vaccinated age groups. [29]