Ann: Leiden Testing Indicates MPL SARS-CoV-2 Antiviral Activity, page-30

AAlso the consensus at the moment is that antibodies post vaccination only last for up to 6 months , not to mention the cost of vaccines and difficulty in obtaining , storing and distributing them in 3rd world countries - refridgeration/freezing/ defrosting etc. Hopefully a tablet would be a cheaper option for those , there are also people that can't be vaccinated due to severe allergies or other reason where MPL may be the better option. I would not worry too much about vaccine roll outs , I believe MPL will have it's place. And let's not forget new mutations popping up everywhere as well.