To overcome pre-existing immunity to the adenovirus in vaccinated individuals, a plausible approach could be using a heterologous recombinant vector as in the Gam-COVID-Vac (Sputnik V) vaccine, the only heterologous COVID-19 vaccine that uses both adenovirus 26 (Ad26) and adenovirus 5 (Ad5) as vectors to express the SARS-CoV-2 S protein [70,75]. The gene discussed is PROS1; the disease is COVID-19.