1. https://www.who.int/news-room/fact-sheets/detail/pneumonia
2. https://www.unicef.org/press-releases/one-child-dies-pneumonia-every-39-seconds-agencies-warn
3. https://www.mayoclinic.org/diseases-conditions/pneumonia/symptoms-causes/syc-20354204
4. https://www.health.com/condition/pneumonia/types-of-pneumonia
5. https://www.medicalnewstoday.com/articles/pneumonia-and-covid-19#relationship