One thing making the development of an effective vaccine or drug against the novel coronavirus so difficult is the fact that a virus constantly changes over time. Some six months into the pandemic, researchers worldwide have already registered 100 different variants of SARS-CoV-2.

This is a normal development because the genetic material of viruses gradually mutates, creating new subtypes. These mutations can also change the characteristics of a virus, causing the original virus to either weaken or become more aggressive.

These different variants also explain why a virus can trigger infection waves of varying severity in different regions of the world, and why infections can also progress very differently in different people.

Fear of second wave in China

China, the country where the pandemic originated,  had largely brought the spread of SARS-CoV-2 under control by imposing strict restrictions on movement. In recent weeks, infections had been found almost exclusively in people returning from abroad. 

Now, however, new infections have again been reported in some Chinese provinces, and this time the infections have obviously taken place in China.

Initial tests have also shown that a new variant of the virus is now apparently circulating in China. The SARS-CoV-2 currently being found in Beijing differs slightly from the strain that previously afflicted China, Zeng Guang, an epidemiologist at the Chinese Health Bureau, told the Global Times  newspaper. The results are now to be compared with analyses from other countries to trace the lineage of the virus.

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A new source of transmission?

The current trail of virus infection has led Chinese health authorities to cutting boards in Beijing's Xinfadi wholesale market on which imported salmon had been processed. It is still unclear where the salmon came from, as China imports the fish from several countries, including Norway, Chile, Australia, Canada and the Faroe Islands.

It is very surprising that salmon is now being thought responsible for the transmission of the coronavirus to humans because the risk of infection is highest from certain mammals. These include camels, horses, sheep, rabbits, martens, ferrets and cats. In contrast, fish, reptiles, amphibians and birds have been shown by many studiesto be unlikely vectors of infection. What is decisive here is the structure of the ACE2 enzyme in the host animal, because the coronavirus has to dock into this enzyme in order to enter a body cell.

As a precautionary measure, the Xinfadi market was closed this past weekend. Around 10,000 dealers and employees at the market are now to be tested for SARS-CoV-2 as quickly as possible. 

In addition, several apartment blocks in the south of Beijing were sealed off, and nine schools and kindergartens were closed. The planned opening of primary schools in Beijing has been postponed, and sports events and group trips to other provinces have all been canceled.

How do mutations occur?

To multiply, viruses use a host cell. When viruses infect such a host cell, they insert their genetic information into it. As a result, the body cells reproduce millions of copies of the virus. However, in each of these reproductions, small copying errors occur. Each of these errors also changes the genetic code of the virus — it mutates.

It has not yet been clarified beyond doubt where and how the novel coronavirus first appeared in humans. So far, researchers have assumed that the first mutations spread in Wuhan, China. The protein with which the virus docks to the cells probably mutated in a host animal, possibly a bat, a pangolin or a tanuki. This mutation allowed the virus to be transmitted to human cells.

Normally, the human body is capable of protecting itself against such viruses. It produces antibodies that defend it against viral attacks and make it immune. 

However, if the virus has already mutated and the antibodies formed are programmed to an older version of it, then these antibodies are much less effective.

This is the reason we regularly get colds and sniffles: Although our body has already produced antibodies against the last virus, it has not yet come up with new antibodies to fight the newly mutated one.

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Are mutations dangerous?

There is much to suggest that the new wave of infections in China is being caused by a new mutation because this time the symptoms develop more slowly.

However, there is no reason to panic, because a mutation does not necessarily make a virus more dangerous. In fact, some mutations can significantly weaken it.

Christian Drosten, a leading German virologist from the Charite hospital in Berlin, also sees any mutation of the novel coronavirus in quite a positive light. He believes it could enable the virus to "replicate even better in the nose and also be transmitted more effectively," Drosten says, pointing to recent studies.

A mutation that primarily affects the nasal area could enable the virus to multiply better, something which "leads to virus epidemics actually becoming more harmless over time," said Drosten in his podcast with the German public broadcaster NDR.

Although virus could continue to infect the mucous membranes in the lungs, Drosten said, this would result in people feeling much sicker than with a cold, so they would end up staying at home and thus avoid passing it on further. This would mean that the virus could no longer spread so well, he said. 

Read more: Coronavirus: Hope in the science of 'superspreaders'

Mutated into oblivion

Mutations can even lead to a virus becoming so weak that it eventually disappears completely. This was the case, for example, with the severe acute respiratory syndrome (SARS) virus.

Starting in November 2002, the first SARS pandemic spread from southern China to almost all continents within a few weeks. As the first pandemic of the 21st century, it aroused great fears among the global population. However, SARS ended up claiming only 774 lives worldwide within six months.

By the summer of 2003, the number of newly infected persons worldwide was declining continuously, and in May 2004, the World Health Organization already declared this first SARS pandemic to be over.