As the task force devised the most efficient system to safely stream the most people through inoculation centers, they used troops to build confidence in the system. People could see the vaccines were safe as soldier after soldier got shots.

At the same time, the task force made a point of showing doctors and nurses getting their shots, as well, to drive home the message of vaccine safety.

While other countries have featured doctors, nurses, police officers and soldiers in their vaccine campaigns, Admiral Gouveia e Melo said the consistency of the messaging was critical.

Still, as the campaign moved onto younger age groups over the summer — with less than half of the public vaccinated — there were signs that resistance was building.

In a submarine, the admiral said, you are in a slow ship trying to catch faster ships.