These two important factors will affect how easily the omicron spreads – VG

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The omicron variant has spread rapidly in South Africa, and probably led to several outbreaks in Norway.

The health authorities believe that it is very likely that omicron will spread more easily than previous variants, but it is currently difficult to say why.

We know the reproductive number, ie the R-number, which says something about how many one infected person on average infects further.

If the R number is 3, one infected person will infect three others on average. This number is affected by various factors, such as how much contact we have and how many have been vaccinated. This number is also called Rt or effective R.

The various virus variants also have a basic R-number, R0, which says something about the virus’ ability to spread before someone is vaccinated or infected – that is, in a completely unprotected population.

This makes some varieties spread more easily

The omicron variant can in practice spread more easily than other variants for two reasons:

• Increased infectivity
• Evades immunity

There are several factors that can cause increased infectivity, such as how long you are contagious, or how much virus you have in your body.

However, if the virus escapes immunity, it will more easily turn away from the protection that was built up after undergoing an infection or vaccine. It thus has the potential to infect more people.

Omicron protection

There is not yet good data available about the omicron variant, but one may get an indication of the dispersibility through what is currently known.

Assistant health director Espen Rostrup Nakstad said the following about the outbreak after the Christmas table in Oslo:

– It says that it is at least as contagious as the delta variant, but it also says that the vaccines protect less against the spread of infection, he says.

Recent data from South Africa also indicate that people who have already undergone covid-19 have a three times higher risk of being infected with omicron than with delta. In other words, there are signs that the variant evades immunity from a past infection.

The delta variant can thus in principle have a higher R0 number than omicron, but omicron can still become dominant because it can infect people who are protected through vaccines or have undergone infection to a greater degree than other variants.

A lot can affect the R-number

– Does it look like it is higher R0 or higher effective R?

– I can not say with certainty what is the correct answer to this, but it looks to the highest degree that this virus has properties that at least in South Africa gives significantly higher infectivity, says health director Bjørn Guldvog.

He points out that we rather know for sure how different measures will affect the omicron variant, or how the variant is affected by the vaccines.

– We have to get back to that, this is what we are now looking for. Then we also look at how this variant is affected by our climate and our way of life, which may be different from South Africa, says Guldvog.

It is colder in Norway and we are more in, he points out.

– In principle, it can lead to higher infectivity. But there may also be characteristics of the variant that make cold not an advantage. For the time being, we are hesitant and need more knowledge, he says.

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