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Scientists say the world has reached a precarious point in the Covid-19 pandemic, where conditions are ripe for the emergence of newer variants of the coronavirus that can complicate efforts to control the disease.
The virus continues to spread rapidly in many parts of the world, even with segments of the population gaining some degree of immunity as a result of being infected or vaccinated.
Scientists say the combination – high rates of viral transmission and a partially immunized population – stimulates the emergence of variants that are potentially more transmissible or lethal. More transmission means more opportunities for the virus to evolve, they say.
“If everyone has immunity, you will have virtually no viruses circulating and the virus will not be able to adapt,” said Bern University molecular epidemiologist Emma Hodcroft, adding that if no one within a population has immunity, there is no pressure on the virus to evolve. “That part of the middle, where you have a partially vaccinated population, or a partially immune population with a lot of viruses circulating, that is your danger point,” she said.
ARCHIVE – In this January 15, 2021 archive photo, a CVS pharmacist prepares a COVID-19 vaccine for residents of the Harlem Center for Nursing and Rehabilitation, a nursing home in the Harlem neighborhood of New York. (AP Photo / Yuki Iwamura,
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New variants may also reduce the effectiveness of Covid-19 vaccines and treatments and lead to reinfections among people who have already recovered from Covid-19, say the scientists. The key to minimizing these problems, they say, is social distance and other measures to reduce contagion, as well as increased vaccination efforts, which have lagged behind in many places.
“The slower you are in these two things, the greater the risk that more variants will emerge,” said Richard Lessells, infectious disease specialist at KwaZulu-Natal Research Innovation and Sequencing Platform in Durban, South Africa, the group of scientists who first sequenced the South African variant, B.1.351.
When a virus infects someone, it creates many copies of itself. Each time this happens, mistakes can be introduced into your genetic code. Some of these errors, or mutations, do not affect the behavior of the virus. Others – like some of those seen in the worrying variants that have emerged in the UK, South Africa and Brazil – can increase the virus’s ability to escape our immune defenses.
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It is a matter of simple mathematics: more transmission means more mutations and a greater likelihood of dangerous variants occurring.
“Each round of virus replication is an opportunity for him to incorporate a new mutation,” said Vineet Menachery, a virologist at the University of Texas Medical Branch. “If you have fewer infected people and fewer rounds of the virus to replicate, that means fewer mutations that can be introduced.”
And if the virus is spreading uncontrollably within a population that has only partial immunity, then variants that have advantageous mutations – for example, those that help it prevent the immune response – tend to predominate, say the scientists.
This phenomenon, called selective pressure, may help explain how some of the new variants of the coronavirus came about, and why South African doctors and scientists reported seeing an unusually high number of suspected reinfections.
“This is what we have seen happening here, almost certainly,” said Lessells of South Africa.
Research by Dr. Lessells and his colleagues showed that variant B.1.351 initially spread more rapidly in the South African province of Eastern Cape, where many residents had previously contracted Covid-19 and recovered. He and his colleagues also showed in a series of laboratory experiments that antibodies from previously infected individuals were less effective against B.1.351 than previous variants of the coronavirus.
Data from another study in South Africa appeared to support these findings, suggesting that the previous infection may not fully protect against infection by the variant.
Bus driver with protective mask working during COVID-19 (iStock)
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Some researchers say that the high number of mutations seen in variant B.1.351 – more than 20 – suggests that the mutations appeared in a single patient before spreading to others.
Some scientists believe that this is what happened in the United Kingdom, where a variant with about two dozen mutations appeared in December. An article published in the journal Nature documented the case of an immunocompromised patient whose Covid-19 infection persisted despite several months of treatment with convalescent plasma. Laboratory tests with virus particles taken from the patient showed that they had developed mutations that made them less vulnerable to antibodies.
That patient’s case shows how selective pressure can work both within individuals and between populations, said Ravindra Gupta, professor of microbiology at the University of Cambridge and co-author of the article. In this patient, the virus learned to live with the patient’s antibodies through favorable mutations that arose spontaneously, he said. What started out as a small mutation in a virus, quickly turned into many more viruses, because there was a lot of replication going on, he added. “It is the same with populations,” he said.
The rate of new Covid-19 infections in the U.S. has declined in the last few days from a peak last month. The pace of vaccinations has recently increased after a slow implementation marked by fragmented communication between federal and local vaccination authorities, distribution bottlenecks and other problems.
Worldwide, Covid-19 infected more than 110 million people and killed more than 2.4 million.