COVID-19 has been raging around the world for two years and still does not think to subside, while the Wuhan coronavirus has mutated several times, adapting to the human body. Although researchers and doctors have learned a lot about the virus and have developed methods of treating and preventing infection that save many lives, the race between the virus and scientists continues. Free News tells about the results of the 2021 pandemic, the main studies and changes that have happened with SARS-CoV-2.
The dominant strain
By the end of 2021, the number of COVID-19 cases has reached almost 300 million people, and 5.4 million deaths, and continues to grow. During this time, the delta variant of the SARS-CoV-2 coronavirus, which was detected in India back in December 2020, has spread across the planet. By November of this year, it was recorded in 179 countries and recognized as the dominant strain, replacing the previous variants. This became possible due to mutations that affected the genes encoding the spike protein (S-protein). The S-protein interacts with the ACE 2 receptor on the surface of human cells, which is necessary for the virus to penetrate inside. Mutations in the S-protein affect not only the transmissibility of the virus, but also its neutralization by antibodies.
It is believed that the delta variant of SARS-CoV-2 is the most contagious of the viruses affecting the respiratory system. It is 40-60 percent more contagious than the alpha variant (British strain), and 225 percent more contagious than the original strain. The coronavirus reproduction index (the average number of people who become infected from one case) increased from 2.4-2.6 to 5-9. For comparison, the following viral infections have reproduction indices: 0.2-0.8 (MERS), 1.2-1.4 (seasonal influenza), 1.4-1.8 (Ebola virus), 2-4 (colds and seasonal acute respiratory infections), 3.5-6 (smallpox) and 10-12 (chickenpox). Chinese scientists have published data that the respiratory tract of people affected by the delta variant contains a thousand times more copies of the virus than people with other strains of coronavirus.
Despite the fact that delta was found to be of concern due to greater resistance to neutralizing antibodies, immunity preserved after recovery from the alpha variant of coronavirus or developed through vaccination remains effective in preventing severe COVID-19 or hospitalization. According to some studies, vaccinated people with a confirmed diagnosis of COVID-19 have a lower viral load on average. Not all specialists have confirmed this; however, such patients remain contagious for a shorter period of time.
The delta variant, also known as the Indian strain, led to the deadly second wave of the coronavirus pandemic in India, which began in February 2021. From here, the wave spread to other countries: Fiji, Great Britain and South Africa, and then to the whole world. This has led to an increase in morbidity, mortality and breakthrough infections that occur despite the vaccine being made. Some health experts have expressed concern that the new strain has made achieving collective immunity impossible due to the fact that it can be transmitted among those who have been vaccinated. However, studies have shown that even in this case, full coverage of the population with vaccines will significantly slow down the evolution of the virus and reduce the pandemic to zero.
Early studies have shown that the delta variant of the coronavirus causes more severe COVID-19 than other strains. Patients with a positive delta test are more likely to develop pneumonia or need an oxygen mask than people infected with the classic or alpha variant. At the same time, the risk of hospitalization more than doubled the risk of getting into the intensive care unit increased by 287 percent, and the probability of death increased by 137 percent.
The new omicron variant of SARS-CoV-2, recorded in South Africa, became known on November 24, 2021, and two days later the WHO designated it as an option of concern. This strain is characterized by an unusually large number of mutations. Compared to the classic Wuhan strain, it has an additional 60 mutations, with 32 of them affecting the S-protein. Many genetic changes are not observed in other variants.
Despite the statements that have appeared that omicron may have an artificial origin, the abundance of mutations can be explained by the fact that the virus has evolved for a long time in the body of a patient whose immune system is significantly weakened. In this regard, scientists suggest that its appearance is associated with HIV infection in a patient infected with SARS-CoV-2. In addition, viruses tend to exchange genetic material, so one of the mutations could have been obtained from the HCoV-229E coronavirus, which causes the common cold.
It is reported that the probability of getting to the hospital in patients with the omicron strain is 50-70 percent lower than in patients with delta. Omicron variant viruses spread in bronchial tissues 70 times faster than previous strains, however, it is assumed that they do not penetrate deeper into the lungs and are less likely to cause pneumonia and acute respiratory distress syndrome.
However, despite the information that omicron causes a disease of lesser severity; it is characterized by greater transmissivity, evasion of the immune system and resistance to vaccines. Even if this strain is indeed milder than the delta variant, it can put a heavy strain on the healthcare system due to an increase in the number of hospitalizations due to a larger number of infected. By the end of 2021, the omicron variant had been discovered in more than 80 countries on all continents except Antarctica. It actively replaces the delta strain and in 2022 is likely to become the dominant form of SARS-CoV-2.
According to experts and health officials, omicron is the most significant threat since the beginning of the pandemic. However, according to the latest data, booster doses of the vaccine are able to restore the body’s defense to the level characteristic of alpha and other coronavirus strains (about 80 percent).
The difficulty with vaccines
In March 2021, scientists faced unforeseen and rare complications after some vaccines, expressed in a violation of blood clotting. These vaccines – from Oxford-AstraZeneca and Johnson & Johnson – are based on adenoviruses, and doctors have reported their suspected connection with thrombosis. Although it was initially believed that vaccines do not affect the development of thrombosis, studies have shown that there is a causal relationship between them. In some countries, the use of vaccines has been suspended pending clarification of details about possible complications.
The ChAdOx1 viral vector became the basis for the Oxford-AstraZeneca Vaxzevria vaccine, and the HAdV-D26 adenovirus-based vector became the basis for the Johnson & Johnson vaccine. A very small number of recipients who received one of these vaccines developed a dangerous blood clotting disorder, also called thrombosis with thrombocytopenia syndrome (TTS).
In December 2021, scientists revealed the probable mechanism of complications. It consists in binding the adenovirus to platelet factor 4 (or antiheparin factor, SPF 4), which causes a chain reaction leading to the formation of blood clots. After injection, the adenovirus binds to PF4, but in very rare cases it enters the bloodstream, where, in combination with PF4, it causes a reaction of the immune system, which considers both molecules as foreign.
An inappropriate immune response releases antibodies against the antiheparin factor. In turn, these antibodies bind to platelets, causing them to stick together and form blood clots. However, this happens in extremely rare cases, and experts emphasize that the benefits and safety of adenovirus vaccines outweigh the possible risks.
A blow to the body
The SARS-CoV-2 coronavirus differs from other respiratory viruses in that it is able to infect the body systemically, causing a malfunction in the immune system and affecting the functions of various tissues and organs. Identification of mechanisms is necessary to prevent the severe course of COVID-19; however, experts still do not understand all the details of such an impact. For example, an immune failure is expressed not only in a cytokine storm, but also in lymphopenia — a decrease in the number of lymphocytes fighting the pathogen.
Infection often leads to neurological problems – they are detected in almost 84 percent of patients. Patients often report loss of taste and sense of smell; some of them have clouded consciousness. There have also been cases of strokes, seizures and even mental disorders. At first, this was explained by the fact that SARS-CoV-2 attacks nerve cells, but later researchers refuted the alleged neurotropy of the virus. It turned out that it does not affect nerve cells directly, as it was shown, for example, on lymphocytes. That is, the loss of sense of smell is not caused by the penetration of the virus into the cells of the olfactory bulb.
Scientists have shown that the coronavirus affects endotheliocytes – cells lining the vessels of the blood-brain barrier. This leads to cell death and vascular destruction. As a result, the blood supply to the brain decreases, oxygen and glucose starvation develops.
According to WHO representatives, based on the current situation with the spread of coronavirus, the future of the COVID-19 pandemic remains uncertain. Scientists are considering several scenarios, according to one of which the omicron variant of SARS-CoV-2 with its reduced pathogenicity is a harbinger of the fact that COVID-19 will gradually turn into a seasonal cold virus. However, the pandemic itself is in full swing and will not decline in the near future until vaccine coverage reaches at least 70 percent of the world’s population. Even in this case, the Wuhan coronavirus will not disappear completely, but will turn into an endemic infection, that is, local outbreaks will occur, as it happens with ordinary SARS.
Currently, scientists are studying the omicron variant to determine how seriously it can affect acquired immunity from COVID-19 and the epidemiological situation in general. Despite the fact that many doctors report that the omicron variant causes a lighter COVID-19, any predictions should be made very carefully, and all efforts and measures should be directed to the prevention of SARS-CoV-2 and the development of new treatment methods.