B. Jacobson, “Heterologous vaccination of BNT162b2 in Ad26. COV2.S-vaccinated healthcare workers elicits long-term humoral immune response”, S Afr Med J, vol. 112, no. 10, pp. 828–837, Sep. 2022, doi: 10.7196/SAMJ.2022.v112.i11.16614.