Sars-Cov-2 evolutions and scenarios according to the experts heard by El Pais
Viral evolution experts argue that SARS-Cov-2 is very likely to stop killing and produce only mild symptoms in children – we read in El Pais.
The world has just entered a new phase of the pandemic with the start of mass vaccinations, on which much depends on what will happen in the coming years with the new coronavirus. Most experts believe SARS-CoV-2 will never go away, but it doesn't have to be a bad thing. When the majority of the population is vaccinated, the pathogen will begin to wear off, producing an asymptomatic infection in adults and only a mild cold in children, according to a study recently published in Science.
The authors base this claim on a mathematical model that reproduces the spread of the virus. Other independent experts in viral evolution and immunology support their conclusions.
"Our model suggests that this transformation will take one to ten years," Jennie Lavine, a researcher at Emory University (US) and first author of the study, told this journal.
The exact time frame will depend on how quickly the virus spreads and the speed of vaccination, he explains. A more complex factor also plays a role: how long a person is immune to severe Covid after being infected or receiving the vaccine. “Ideally, the ability to block the disease should be lasting, but the ability to transmit it should be shorter,” Lavine says. There is a final factor: how many infections or vaccine doses will be needed to build strong immunity?
This transition will mark the transition from a pandemic to an endemic virus, which means it will always be present and can cause occasional outbreaks without much virulence.
Scientists believe SARS-CoV-2 is more similar to the four known cold coronaviruses than the two most virulent, SARS 2001 and MERS 2012. In this case, when most of the population is vaccinated, the virus is not it will be more capable of causing serious illness, as vaccines prevent it. It remains to be seen whether the injections also prevent transmission of the virus, which is less likely. In this way, the only ones who will remain virgins of the virus will be the babies who will be born, but they will have only mild symptoms and colds. This is already the case with the four known seasonal coronaviruses.
Based on what is known about the rest of the cold coronaviruses, researchers estimate that the first infection in children will occur between three and five years of age. Children can be reinfected in later years, but symptoms would be milder or more absent. “These findings reinforce the importance of continuing isolation measures until vaccination campaigns are completed during this pandemic phase. It may be necessary to continue vaccination in the endemic phase ”, explain the authors.
One of the keys to this possible future is the duration of immunity after infection or vaccination. The authors believe that both protect against serious disease, but perhaps not mild reinfection – the presence of the virus in the body and its possible transmission. The presence of the virus would strengthen the body's defenses, making it more immune to subsequent infestations of the pathogen.
The emergence of more contagious variants, like that of the UK , could make things better, Lavine said. A variant that spreads faster but is no longer lethal will lower mortality. In addition, it would increase people's immunity, as an asymptomatic infection would strengthen the defenses. And ultimately it would keep our immune systems "up to date" with the latest variants of the virus. All of this could collapse if a variant emerges that causes more serious disease, putting all unvaccinated people at greater risk. Lavine explains that, based on the four cold coronaviruses, there is no evidence that this could happen. "It's not impossible, but we don't have any evidence to believe it's likely," he says.
"The most reasonable thing is that in this decade this virus will become endemic and will only produce seasonal peaks in the winter," Mark Lipsitch, a Harvard University epidemiologist, told this paper. In May 2020, his team calculated that there will continue to be peaks of infection with this coronavirus until at least 2024. The researcher justifies his opinion. “The impact of this virus on public health will dramatically decrease when one of the two conditions is met. The first is that, as this study says, immunity to severe brood will be long lasting and will also be strengthened through mild reinfections, because there is no total immunity. The second is that there is vaccine coverage in the people most at risk, in order to significantly reduce mortality. I believe the first thing that will happen in the whole world. The developed countries will have covered vaccination in six months or a year and the other countries some time later, ”he explains.
In any case, the work is based on another reasonable but unproven hypothesis. SARS-CoV-2 is not the same as its four cold relatives and it is unknown how long immunity to the serious illness it produces lasts. “Even if it's pure speculation, it's possible that older people don't maintain immunity to SARS-CoV-2 as effectively as they do to cold viruses,” Lipsitch said.
The team of Cristina Calvo, head of pediatrics at the La Paz hospital in Madrid, has been studying phlegm coronavirus infections in children for 14 years. "Viruses adapt and become mild or disappear because they no longer have hosts," he explains. "The logical thing is that they lose their pathogenicity and their lethality," he adds.
“This virus is practically impossible to eradicate”, explains Toni Trilla, epidemiologist at the Clinical Hospital in Barcelona. "I agree that in the future this virus will look more like the cold coronavirus than SARS and MERS," he adds.
The virus will not go away because it can always find refuge in some people or animals. This is similar to what's already happening with the flu, whose reservoir is made up of wild waterfowl and which returns every winter changed enough to require a new vaccine. Sometimes the flu is seasonal and not very serious, and sometimes it can be a pandemic variant, such as the one that killed 50 million people in 1918 and 1919.
This coronavirus has already been shown to pass from humans to pets and farm animals, such as mink, and two gorillas from the San Diego Zoo were recently spotted infected by a visitor, recalls María Montoya, head of viral immunology of the Margarita Salas Biological Research Center. Also, the vaccine does not protect 100%, so the coronavirus will always be able to find cracks to get through. "If the vaccination fails or if the second dose is delayed too long, or if the second dose is not given, the protection is not optimal, so the infected person cannot suffer from the disease, but they can harbor the virus," he explains.
Another possible reservoir is constituted by immunosuppressed people, with weakened defenses, where, as recent studies suggest, the virus can mutate and acquire some resistance to certain antibodies, the proteins of the immune system that theoretically prevent it from entering cells to infect. “It's like when people don't take antibiotics for the prescribed days and stop halfway; they are selecting pathogens that survive and may become more resistant to treatments or vaccines, ”Montoya said.
Another very difficult aspect to predict is the evolution of this virus. Sars-CoV-2 sheds less than influenza. This means that it accumulates fewer changes in its genome each time it copies into a cell. But keep in mind that a single virus can make tens of thousands of copies of itself using a single human cell. And humans have billions of cells.
Add to that the number of infected people worldwide, over 90 million confirmed people, but probably more. So even if it sheds little, it has millions of opportunities to do so in every infected person.
So far the virus has evolved naturally: there have been few effective treatments or vaccines against it. A second phase of its evolution is now beginning characterized by the pressure that vaccines will exert on it. “Variants with potentially dangerous mutations such as those found in the UK or South Africa will become much more numerous as vaccination takes hold and reaches more and more people. The virus will mutate in an attempt to escape the immune systems of those who have been vaccinated, and many more complex variants will appear. If the virus changes too much, then current vaccines may need to be changed, ”Montoya warns.
What we have observed so far allows us to be moderately optimistic. A recent study showed that the BioNTech vaccine can neutralize the British variant. The key is that the vaccine generates antibodies and memory cells for many different parts of the spicule protein, which protrude onto the surface of the coronavirus that serves to bind to human cells, enter them and hijack their biological machinery to reproduce. Even if they change – mutate – one or more pieces of that protein, the immune system will still recognize the rest and be able to neutralize the virus.
Another point of uncertainty is that this coronavirus is genetically more similar to the virulent viruses of SARS and MERS than to those of the cold. “Highly pathogenic coronaviruses differ from mild ones by the greater number of accessory genes,” explains Isabel Sola, a virologist at the National Center for Biotechnology (CSIC). "These genes often contribute to increased virulence, because they inhibit the innate immune response, the first line of defense that prepares and promotes the adaptive immune response, with antibodies, and T lymphocytes. It is possible that while these genes remain in the virus, it is more complicated that it becomes a virus that causes mild infections ”, he warns.
Chances are we are already seeing the birth of a new virus that will never go away, but that will be infinitely more manageable. "It is still impossible to know the final fate of this coronavirus, but it is reasonable to suggest that it will join the four endemic coronaviruses that cause us colds every year," said Miguel Hernán, an epidemiologist at Harvard (USA) and scientific advisor to the government. “It is possible, in fact, that these endemic coronaviruses were also responsible for plagues or parasites of antiquity. Deadly epidemics then and uncomfortable colds now. If endemicity is the end result for subsequent generations, the sooner we vaccinate all adults, the more lives we will save in this generation, ”he adds.
Article taken from the foreign press review of Eprcomunicazione
This is a machine translation from Italian language of a post published on Start Magazine at the URL https://www.startmag.it/sanita/sars-cov-2-fra-10-anni-provochera-solo-un-raffreddore/ on Sat, 16 Jan 2021 06:09:24 +0000.