<a href="https://www.nejm.org/doi/full/10.1056/NEJMc2101667" target="_blank" rel="noopener nofollow">https://www.nejm.org/doi/full/10.1056/NEJMc2101667</a><br><a href="https://www.mhlw.go.jp/content/10900000/001132657.pdf" target="_blank" rel="noopener nofollow">https://www.mhlw.go.jp/content/10900000/001132657.pdf</a><br><a href="https://www.bundesgesundheitsministerium.de/en/coronavirus/faq-covid-19-vaccination.html" target="_blank" rel="noopener nofollow">https://www.bundesgesundheitsministerium.de/en/coronavirus/faq-covid-19-vaccination.html</a><br><a href="https://www.cdc.gov/coronavirus/2019-ncov/vaccines/stay-up-to-date.html" target="_blank" rel="noopener nofollow">https://www.cdc.gov/coronavirus/2019-ncov/vaccines/stay-up-to-date.html</a><br>