Nigeria, May 20 -- The small archipelago nation of Seychelles, northeast of Madagascar in the Indian Ocean, has emerged as the world's most vaccinated country for COVID-19.

Around 71% of people have had at least one dose of a COVID vaccine, and 62% have been fully vaccinated. Of these, 57% have received the Sinopharm vaccine, and 43% AstraZeneca.

Despite this, there has been a recent surge in cases, with 37% of new active cases and 20% of hospital cases being fully vaccinated. The country has had to reimpose some restrictions.

How can this be happening? There are several possible explanations:

What does the country's experience teach us about variants, vaccine efficacy and herd immunity?

Let's break this down.

Variants can escape va...