1. Public Health Agency of Sweden. Basis for Decision on the Recommendation of a Second Booster Dose (dose 4) of Covid-19 Vaccine, 2022. https://www.folkhalsomyndigheten.se/publicerat-material/publikationsarkiv/b/beslutsunderlag-om-rekommendation-av-en-andra-pafyllnadsdos-dos-4-av-covid-19-vaccin/. Accessed 1 April 2022.
2. European Centre for Disease Prevention and Control. COVID-19: Joint statement from ECDC and EMA on the administration of a fourth dose of mRNA vaccines, 2022. https://www.ecdc.europa.eu/en/news-events/ema-ecdc-statement-fourth-covid-vaccine-dose. Accessed 8 April 2022.
3. Protection by a Fourth Dose of BNT162b2 against Omicron in Israel;Bar-On;N Engl J Med,2022
4. Fourth dose of BNT162b2 mRNA Covid-19 vaccine in a nationwide setting;Magen;N Engl J Med,2022
5. Effectiveness of a second BNT162b2 booster vaccine against hospitalization and death from COVID-19 in adults aged over 60 years;Arbel;Nat Med,2022