The Dutch study
“In the current Sars-CoV-2 pandemic, a key unresolved question is quality and quality duration immunity acquired in healed individuals“reads the preface to the study, a fundamental question to understand if the virus will be less fearful or not.”They all seem to induce short-term immunity with rapid antibody loss. “ , the researchers said, based on the study of 10 people over a period of 35 years, from 1985 to 2020 with a total of 2473 between observations and monitoring per person in each month of the year, to determine the level of antibodies following infection by one of the four seasonal coronaviruses, the Alphacoronavirus and of betacoronavirus, and the length of time that elapsed between an infection and another of the same virus. Both analyzes found a definite duration “alarming“for protective immunity against coronaviruses, finding new and Frequently infections 12 months after the first and a substantial reduction in antibody levels just six months after contracting the viruses.
Many uncertainties. The researchers point out that it is not yet clear how long the protective immunity derived from Covid-19 can last. According to the study, reinfections will likely be dictated by two variables: “virus exposure and sustained quality of immunity“the researchers write. Put simply, it assesses how long a patient has been under attack by Covid (if the infection has passed in a short time or if it has healed after many weeks) and How many antibodies produced the organism. The antibody response is not the same for everyone: there are those who produce more and less. Clearly, those with multiple antibodies could have a longer, but not infinite, “hold” over time.
Seasonal coronaviruses. Exist four seasonal coronavirus species, all associated with infections along the respiratory tract but mainly minor. In addition to causing common colds, the four viruses are biologically different: two of them belong to the genus Alphacoronavirus, the other two ai betacoronavirus. These viruses use characteristic receptor molecules to enter a “target” cell, but not all of them enter the same type of epithelial cell in the lungs. Due to their variability, seasonal coronaviruses are the most representative viral group from which to derive the general characteristics, the key points are protective immunity and susceptibility to reinfection. Since most people, the researchers explain, experience the first seasonal coronavirus infection in early childhood (4-6 years), from that time on reinfection that happen in the following years. The aim of the study is to shed light on the period of time that passes between coronavirus reinfections and antibody dynamics, as these decrease after infection. These parameters were assessed by measuring the immune response to each individual seasonal coronavirus for an extended period.
Frequency of infections and reinfections. The study was conducted on 10 adult males, started in 1985 and continued until 2020 at regular intervals (every 3 months before 1989 and every 6 months thereafter). At the start of the study, the age of the subjects varied from 27 to 40 years; before the end of follow-up (monitoring), subjects were 49 to 66 years old. This research was approved by the Medical Ethics Committee of the University of Amsterdam Medical Center.
Antibody dynamics after infection. In some cases, reinfections have already occurred six months after the first (out of two patients) and 9 months after (in another patient) but most of the time the new ones contagions they took place from the twelfth month onwards, a bit like many people with seasonal influences. The only “certainty”, therefore, that does not reinfect us before six months. The most important dynamic is represented by the table attached below with the letter C which shows how, within 6 months of infection, the majority of people have lost the 50% of their antibodies, reaching 75% after one year. A complete return to baseline levels occurred within 4 years for half of seasonal coronavirus infections. Therefore, protective immunity can be included in an interval of time ranging, on average, from 6 to 12 months. At the end of the year, he would be exposed again as the first time.
Coronavirus infections in varying seasons. The researchers point out that, to date, it is not clear whether Sars-Cov-2 will also become seasonal and will have a peak in winter prevalence as observed for seasonal coronaviruses in non-equatorial countries. The 4 types of coronavirus object of their study, the Alphacoronavirus and of betacoronavirus, also called “common human coronaviruses”, show a typical seasonal pattern and, from May to September, show the lowest probability of annual infection. The researchers, therefore, in their study specify how, in nature, reinfections occur with all seasonal coronaviruses, most of which within 3 years. If Sars-Cov-2 also behaves like a seasonal coronavirus, a similar trend can be expected.
Serological tests, vaccine and flock immunity: all doubts
Dutch researchers focus on a risk that could arise in the near future: tests based on serology to measure the level of antibodies for Covid-19 infections, they could be practically useless if the infection occurred more than a year before the infection. In addition, studies on vaccines they should anticipate that prolonged protective immunity may be uncertain for coronaviruses and that annual or semi-annual vaccinations may be required to circumvent ongoing transmission. The same uncertainty speech is related to herd immunity, which occur when a high percentage of the population becomes immune to a certain pathogen, also protecting non-immune individuals against infection and limiting their overall spread. This effect has been observed for a variety of viruses such as hepatitis A, influenza A virus and human papilloma virus. However, in the case of Covid-19, achieving herd immunity may be very unlikely due to the rapid loss of protective immunity. The researchers, for their part, emphasize how, to confirm this, they will be “needed more screening, our study was restricted “, including the inability to sequence the Covid genome during infection. “In conclusion, seasonal human coronaviruses have little in common, besides causing a cold – say the scholars – However, they all seem to induce immunity short durability with rapid loss of antibodies. This could also be a common denominator for human coronaviruses“.