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:

1. the herd immunity threshold has not been reached — 62% vaccination is likely not adequate with the vaccines being used
2. herd immunity is unreachable due to inadequate efficacy of the two vaccines being used
3. variants that escape vaccine protection are dominant in Seychelles
4. the B1617 Indian variant is spreading, which appears to be more infectious than other variants
5. mass failures of the cold-chain logistics needed for transport and storage, which rendered the vaccines ineffective.

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

Let’s break this down.

Variants can escape vaccine protection

There are reports of the South African B.1.351 variant circulating in Seychelles. This variant shows the greatest ability to escape vaccine protection of all COVID variants so far.

In South Africa, one study showed AstraZeneca has 0-10% efficacy against this variant, prompting the South African government to stop using that vaccine in February.

The efficacy of the Sinopharm vaccine against this variant is unknown, but lab studies show some reduction in protection, based on blood tests, but probably some protection.

However, no comprehensive surveillance exists in the country to know what proportion of cases are due to the South African variant.