evidence: Many COVID-19 vaccine clinical trials are in process. Researchers take what was previously learned from vaccine studies of SARS-CoV, MERS-CoV and other viruses to develop vaccines that prevent COVID-19. Researchers also study COVID-19 symptoms, long-term effects, diagnostic tests, antibody tests, treatments and drugs. [...] The FDA gives emergency use authorization to two mRNA COVID-19 vaccines, the Pfizer-BioNTech and the Moderna COVID-19 vaccines. Because there is an urgent need for COVID-19 vaccines and the FDA’s vaccine approval process can take months to years, the FDA first gave emergency use authorization to COVID-19 vaccines based on less data than is normally required. The data must show that the vaccines are safe and effective before the FDA can give emergency use authorization or approval. Vaccines have gone through — and continue to go through — extensive safety monitoring. Millions of COVID-19 vaccines have been given since December 2020. Researchers at Mayo Clinic and other medical centers continue to study more vaccines that prevent COVID-19.