What are the variants of Covid-19? – Quartz

New variants of SARS-CoV-2 have now escaped New Zealand border protections twice to spread throughout the community.

In the most recent outbreak, which placed Auckland in an Alert Level 3 lockdown, there are three active community cases of the more infectious B.1.1.7 lineage.

Although we have seen the virus mutate throughout the pandemic, it was not until mid-December 2020 that variants with noticeably different behavior emerged.

There are several reasons for this, including the continued exponential increase in cases around the world. Each case of COVID-19 gives the virus a chance to mutate, and if the number of infections continues to rise, new variants are likely to emerge.

Press to mutate

The genetic code for SARS-CoV-2 is an RNA string of approximately 30,000 bases or letters. When the virus enters our cells, it hijacks them to make thousands of copies, but the copying process is not perfect.

Errors, or mutations, occur on average once every two weeks in any chain of transmission. Most are single letter changes and don’t make a noticeable difference, but some will change the physical form of the virus, with possible ripple effects on the behavior of the new variant.

We know about these variants through the sequencing efforts of different countries and their open sharing of this knowledge. The variants that have appeared recently – known as B.1.1.7 (first identified in the UK), B.1.351 (identified in South Africa) and P.1 (identified in Brazil) – have all a large number of mutations that have physically modified the virus.

A number of these changes occur outside the virus, in the advanced proteins that it uses to infect cells. Such changes can also compromise the ability of our immune system to detect these new versions of the virus when it has only seen the old version.

The most obvious reason why new variants have emerged recently is that the number of global cases increased massively in the last quarter of 2020. There have been around 35 million recorded cases globally in the first nine months of 2020 , but it only took two months to double that number. We are on track to double that number soon.

Avoid increasing levels of immunity

A second reason is that the virus responds to the immunity that has started to develop in the population. Our immune system plays an important role in determining which mutations survive and are passed on.

The immune system is constantly trying to identify and kill the virus, which can only infect new people if it escapes detection. While mutations occur at random, those that lead to a more transmissible variant or those that escape our immune system are preferentially selected and more likely to persist.

The mutations that characterize B.1.1.7, B.1.351 and P.1 have been shown to spread faster (particularly B.1.1.7) and early evidence points to a difference in immune response (but not in B.1.1. 7).

Another indication that immunity plays a big role is that the B.1.351 and P.1 variants have become prominent in areas with large early waves of COVID-19 where the population has developed higher levels of immunity.

P.1 has been identified in Brazil where up to 70% of the population was infected in the first wave. B.1.351 quickly became the dominant strain in the Eastern Cape region of South Africa, which was also severely affected.

The new variants could infect more people than the virus’s original wild type, which could only infect people who had never been infected before.

This is one of the reasons why, historically, herd immunity for a new virus has not occurred by “natural progression of the disease” but only by vaccination.

The last part of the story is the fact that two of these variants (B.1.1.7 and P.1) differ by up to 25 mutations of the closest known SARS-CoV-2 sequences. This is very unusual given that most of the viral sequences we see are just a few mutations of the others.

Such a rapid increase in diversity has been observed in chronic COVID-19 infections in immunocompromised hosts. Most people are sick for a week or two, but a few have to struggle with it for months. During this time, the virus continues to evolve, sometimes very quickly as a weakened immune system presents all kinds of challenges for the virus but fails to kill it.

This type of infection is a “training ground” for the virus because it is constantly adapting.

Will we see more new variations?

As long as the virus is there, it will continue to mutate. With vaccine protection and natural immunity in an increasing number of people, the pressure on viral variants that escape our immune system is greater.

The rate of new mutations varies greatly from virus to virus. The overall mutation rate of SARS-CoV-2 is about half that of the influenza virus and much slower than that of HIV. But the overall mutation rate doesn’t tell us everything. What really matters is the rate of mutations that physically alter the virus.

There is preliminary evidence that this rate is about the same SARS-CoV-2 as in influenza viruses. One of the reasons for this is that SARS-CoV-2 has only recently reached humans and is not yet “optimized” to spread in humans.

Essentially, the original virus was only a few mutations away from better fitness, and there could be other easy changes that could make it even better suited for humans. Once the virus goes through this initial adaptation phase, there will be fewer possibilities for easy and fitness-enhancing changes and new variants may appear less frequently.

The variants that have been characterized so far are probably only a small subset of those in circulation. It is no coincidence that they are known from countries with comprehensive sequencing programs (notably the United Kingdom).

But the new variants are not the main driver of the transmission on a global scale. Most countries around the world are still susceptible to any variant of SARS-CoV-2, including the original version. The protective measures we have successfully used at Aotearoa to control the virus continue to work for all variants.

The best way to protect against all current variants and to prevent the appearance of other variants is to reduce the number of cases through control measures and ongoing vaccination.

This article is republished from The Conversation under a Creative Commons license. Read the original article.