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  • Writer's pictureWilliam Miller, MD

The Omicron Variant

The news media has been buzzing with articles about a new COVD variant, B.1.1.529, which was first identified about two weeks ago in South Africa. On November 26th, the World Health Organization (WHO) added it to the list of “variants of concern” giving it the Greek letter name Omicron. Personally, I didn’t even know that there was a Greek letter called omicron.

Recall that mutations of viruses occur commonly since the host cells that are taken over by the virus are not designed to reproduce viruses. In the process of commandeering the cell’s machinery to make copies of itself, mistakes will invariably occur when copying the genetic code of the virus. These mistakes are what we mean by the term “mutations”. The vast majority of mutations have no effect one way or the other. Further, a large number of the mutations will actually be detrimental to the virus. On very rare occasions (perhaps one in several million), a mutation will convey some benefit to the virus. However, when you have a worldwide pandemic with very large numbers of people getting infected, each of whom will make millions of new copies of the virus, then something that is very rare still happens frequently enough to be significant.

There are three ways that a mutation of SARS-2, the coronavirus that causes the disease COVID, can be beneficial for the virus. The first and most common is a change in the way the spike protein on the surface of the virus sticks onto the host cell and thus gains entry. Think of it as a key working in a lock. The better the key fits, the more likely the lock will open and let the virus in. This is how the Delta variant was able to become more contagious.

The second most common way is to develop a means of evading the immune system, usually by altering the site on the virus where antibodies attach. This type of mutation is concerning because it might lead to COVID vaccines becoming less effective. For example, this is very common with influenza viruses and is one of the reasons we need to get a new flu shot every year.

The last way, which is the least likely, is that the virus might change its way of replicating so that it is more efficient at reproducing. This could develop over a long period of time, but would require a whole string of mutations and possibly lead to a change in the overall nature of the particular virus. Thus, it is not likely to play a role in changes we see from month to month. This sort of successive mutations adding together over time could lead to an entirely new virus developing, not just a new variant. Of course, that is how we get new viruses like COVID in the first place.

When a new variant develops that has advantages over other variants circulating around in the population, then that new variant will begin to out compete the others and eventually will become the predominant variant. That is what we saw with Delta. Over a few months it rose above the other previous variants, becoming the predominant one worldwide.

This is how all living organisms evolve, including humans. The process is called natural selection. Small mutational changes that give some slight benefit over the competition may lead to the new version eventually predominating, thus replacing other competing versions. Think of modern humans out competing Neanderthals to their eventual extinction.

In South Africa, Omicron appears to be rapidly replacing Delta as the predominant variant. This implies that it has mutations which make it more contagious than Delta. An early analysis suggests that it has at least 32 and possibly as many as 43 mutations involving the spike protein when compared with Alpha (the original variant) and with Delta which has only a dozen on average. Those changes made Delta 40% more efficient at being spread than Alpha. The worry is that mutations to the spike protein may reduce the effectiveness of our current vaccines since that is the attachment site for most antibodies produced by the vaccines.

On the flip side, remember that more mutations do not necessarily mean a more powerful virus. Keep in mind that the vast majority of mutations have no effect on way or the other. The important thing is whether any of those mutations will alter treatment options or assist the virus in evading the immune system.

At this time, it is too early to draw any major conclusions about Omicron, other than it is probably more contagious than Delta based on the way it is rapidly becoming the predominant variant in South Africa. We also know that it has now been identified in Brazil, Holland, Hong Kong and Canada suggesting that it has already spread globally. It is likely to be in the US, just not yet detected.

There are some very preliminary observations that the scientists in South Africa have shared. We should consider these with caution since they may turn out not to be true. One is that Omicron seems to cause a milder case of COVID than Delta. If this is true, then that could be a good situation by having a milder disease variant replace a more serious one as the predominant. However, this may simply be the result of South African cases being skewed for some reason towards a younger population of 20 and 30 year olds as appears to be the case.

The WHO and CDC along with many international scientific organizations are directing resources to learn more about Omicron and to answer these questions as soon as possible. The WHO update this week predicts more solid answers in the next 2-3 weeks. In the meantime, I think it is important not to let our speculations fuel our fears. We should be patient and take reassurance in the fact that masks, handwashing and avoiding crowds, especially indoors, will always be our best defense and cannot not be easily undermined by any mutations of the virus.

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