1. Centers for Disease Control and Prevention (2018) Understanding How Vaccines Work. https://www.cdc.gov/vaccines/hcp/conversations/understanding-vacc-work.html
2. Centers for Disease Control and Prevention (2022) Need Travel Vaccines? Plan Ahead. https://wwwnc.cdc.gov/travel/page/travel-vaccines
3. Centers for Disease Control and Prevention (2019) What’s in Vaccines? Ingredients and Vaccine Safety. https://www.cdc.gov/vaccines/vac-gen/additives.htm
4. OpenWHO (2022) Vaccine Safety Basics.https://openwho.org/courses/vaccine-safety-basics
5. Immunisation Advisory Centre (2020) A Brief History of Vaccination. https://www.immune.org.nz/vaccines/vaccine-development/brief-history-vaccination