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Low vaccination rates might be one reason for variants Image caption: Low vaccination rates might be one reason for variants

The Omicron variant was first identified in South Africa, in a region with relatively low rates of vaccination. But making a link between the two is not straightforward.

The virus mutates as it jumps between people as well as within a sick person. So in a population with a low vaccination rate, there will be more infected people around, and a greater opportunity for the virus to change.

But potentially harmful mutations can take hold when the virus faces new challenges like vaccines – so a population with some immunity but with the virus widely present is a perfect environment for new mutations to emerge.

It follows that a highly vaccinated population where infection rates are low probably provides the best barrier against potentially harmful mutations. The challenge is to get from a low to a high-vaccination environment as quickly as possible.

“A mix is the worst thing, but unfortunately we all have to pass through having that mix to get to the other side,” Prof Rowland Kao, a veterinary epidemiologist says.

Another factor is how many people in a population have suppressed immune systems and could be ill with the virus for a long time, giving it more chance to mutate.

One theory is that Omicron emerged in an immunosuppressed person or population – possibly with untreated HIV which is a big problem in the southern African region. But this is very difficult to prove without knowing exactly where it first emerged.