There are almost 150 coronavirus vaccine candidates under development. Only 19 of these are now being tested in humans. Many types of vaccines are rapidly progressing through clinical trials. Only two vaccine candidates have announced large scale Phase 3 trials, involving several thousands of people. Only one candidate has been approved for restricted human use. Measuring a reduction in COVID-19 levels is an obstacle for Phase 3 clinical trials, as they require a high infection rate among the tested population to prove vaccine efficacy. International agreements with countries where SARS-CoV-2 infection rates are still high are facilitating those trials. Future challenges in vaccine development include a better understanding of COVID-19 immunity and development of vaccination strategies.