Unlocking mission 43
Mission 43 does not become available after finishing mission 41 (Proxy War Without End). Luckily, unlocking it is fairly easy. Focus on completing side-ops - in my case, I had to complete three of them. When you finish a sufficient number of side-ops, you will be called to the Mother Base to listen about an outbreak of a new epidemic. The new mission will appear on the list after a cutscene.
Forty-third mission of Metal Gear Solid V takes place in its entirety on the quarantine platform in the Mother Base. Your task is to stop the outbreak of the new pandemic. The mission is not really original, so finishing it won't take much time or cause too much trouble.
- MAIN (1/2): Identified the person who sent the transmission - Just reach one of the scientists in the quarantine zone.
- MAIN (2/2): Eliminated the infected - Kill the enemies you encounter on your way back. When you eliminate all of the infected, you need to leave the quarantine zone.
Note: This mission will not give you any ranks, but it does count some stats (e.g. Time required for completing it).
Preparing for the mission
The game will not let you prepare. Big Boss's equipment consists only of his current rifle and handgun. You'll only need the former to complete the mission.