A new study on Chile’s national COVID-19 vaccination program, to be presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases (ECCMID 2022, Lisbon 23-26), and published in The Lancet Global Health, shows that giving a different type of vaccine (heterologous) for the third or ‘booster’ dose than was received for the first two doses, leads to better vaccine performance than using the same (homologous) inactivated SARS-CoV-2 vaccine for all three doses.