Is it Underestimated how many people are resistant to Covid-19

During the first wave of the Cave-19 pandemic, cities were generally hit worse by smaller areas or rural areas. However, in Italy, Rome was relatively spared, while the villages of Lombardy had very high rates of disease and deaths. Then, a Lombard village - Ferrara Erbonone - stands out by not noticing a single case of covid-19 during the wave. Nobody knows why, writes the Guardian.

The puzzle is not just Italian. From the very beginning, Covid-19 struck unevenly around the world, and scientists have tried to understand the reasons. Why are some populations or sectors of the population more vulnerable than others? Or to ask the question, why are some groups relatively protected?

At the Observer last weekend, neurologist and cowboy model 19 Carl Friston of University College London said - based on his comparison of German and British data - that the relatively low mortality rates registered in Germany were due to unknown protective factors. .

"This is like dark matter in the universe: we can't see it, but we know it has to be there to take into account what we can see," he said.

While this is a new look - most experts praise Germany's conclusion and the systematic testing mode - others are working hard to identify the factors that modulate the spread of Covid-19 and thus explain other puzzles - as it seems. Japan has avoided a deadly first wave despite a relatively old population and unannounced public health response, or why Denmark, Austria and the Czech Republic have reported no cases of violence despite their early easing of quarantine measures. This can be shaped by how governments manage the risks of a second wave.

One thing is clear: there are many reasons why one population is more protected than another. Theoretical epidemiologist Sunetra Gupta of Oxford University believes that the immunity built before this pandemic is crucial.

- Poor activity that has cross-protection against serious illness and death that give them other circulatory errors. Although this cross-protection cannot protect the person from infection in the first place, it could ensure that they have only relatively mild symptoms, says Gupta.

Gupta's predictions remained just that, due to a lack of data on covid-19 immunity. Antibody testing, as we know, is very short-lived and cannot be considered reliable, and the results so far suggest that the proportions of the population carrying covid-19 virus antibodies are often in single or low double-digit numbers. New, more sensitive antibody tests, which have become available in recent weeks, could soon provide a more accurate picture if deployed wide enough, but there are already hints that the results can still be underestimated.

First, there was evidence based on diagnostic testing of postmortem samples from patients who died in December that the virus had circulated in Western countries - especially France and the United States - about a month earlier than previously thought. New research shows that another component of the human immune response, T cells that help orchestrate the response of antibodies, shows a memory for coronavirus infection when exposed to Sars-CoV-2, the virus that causes covid-19. .

In a paper published in Cell on May 14, researchers at the La Jolla Institute for Immunology in California reported that T cells in the blood extracted from humans between 2015 and 2018 recognized and responded to fragments of the Sars virus. CoV-2 “.

- These people could not see the "Sars-CoV-2". The most plausible hypothesis is that this reactivity is indeed cross-reactivity with relatives of Sars-CoV-2 - ordinary cold coronaviruses that circulate very widely and usually give a fairly mild disease - says one of the newspaper's authors, Alessandro Shet.

The discovery supported the group's predecessor at the Charité Hospital in Berlin, revealing the reactivity of T-cell proteins in the Sars-CoV-2 virus in 83% of covid-19 patients and 34% of healthy volunteers. who were tested negative for the virus itself.

David Hayman, an epidemiologist at the London School of Hygiene and Tropical Medicine, who advises the World Health Organization on covid-19, said the results were important, but warned that cross-reactivity did not have to turn into immunity. Determining whether this means that a large number of people will show such cross-reactivity to see if they are protected, if not from a Covid-19 infection, then at least from severe forms of the disease.

However, it is a reasonable hypothesis that exposure to other coronaviruses may provide protection, Seth said.

- We have seen it before, for example with the "H1N1" flu in 2009. Older people have coped well with other age groups in the pandemic, he said, probably because their immune systems had been prepared for exposure to similar types of flu for decades. That could be the reason why the pandemic in 2009 was less deadly than other flu pandemics in history, killing about 200,000 people globally.

If exposure to other coronaviruses protects against covid-19, Gupta said, then the variability in that exposure could explain much of the difference in mortality rates between states or regions. Exposure to a related virus that caused an epidemic of severe acute respiratory syndrome (SARS) in 2002 and 2004 could provide some protection for East Asians against Covid-19, for example.

In late March, the Gupta Group published a paper that drew attention because it generated very different forecasts from those of epidemiologist Neil Ferguson of Imperial College London and his colleagues - whom the British government listened to the most. The Oxford Group has suggested that up to half of the UK population may already be infected with Sars-CoV-2, which means that the mortality rate of infection (IFR) - the percentage of infected people who have died - is much lower than the group's indications. of Ferguson, and therefore the disease was less dangerous. No group had much data at the time, and Gupta said her intention was to emphasize that, in the absence of data, a wide range of scenarios should be considered.

Two months ago, she stood by her model, but wanted to make the consequences clearer.

"The truth is that IFR is not a hard wire to the virus or our interaction with the virus," she said. "It's the vulnerable faction (of the population) that determines the average overall risk of dying." As soon as the virus is infiltrated in a nursing home, for example, the virus spreads rapidly through it and is often fatal, increasing IFR. This means that it is crucial to understand why some people are resilient and others are not, so that those who are vulnerable can be protected.

We know some of those vulnerabilities. Age is most obvious. Unlike influenza in 2009, older people are particularly vulnerable to covid-19 - a fact that could reflect the history of coronavirus exposure from different age groups. Comorbidity is different, and a third is male. According to Garima Sharma of the Johns Hopkins University School of Medicine in Baltimore, who recently published a paper with colleagues on sexual differences in cow-19 mortality, women are protected by having a "spare" chromosome on H. "X chromosomes contain a high density of immune-related genes, so women generally have stronger immune responses," she said.

Socioeconomic status, climate, culture, and genetic makeup could also create vulnerabilities so that certain vaccines can be given in childhood and vitamin D levels. And all of these factors can vary between countries. The Japanese may have been given some protection, such as the custom of bowing instead of shaking hands. Despite the fact that most of the gender differences lie in biology, Sharma says some of it is due to social factors and behavior, with women more likely to wash their hands and seek preventive care.

It also becomes clear that the protection of the vulnerable has made a big difference in the outcome so far. For example, Italy and Germany have similar proportions to those over 65 - just over 20% of the population in both cases - and yet the two countries have reported incredibly different mortality rates. The death rate in the case (IFR) - the percentage of patients dying - is less informative, but is easier to measure than IFR, because the sick are more visible than the infected, and on May 26 the IFR in Italy was around 14%, compared to 5% in Germany.

Italy is more densely populated than Germany, and Italian homes tend to be smaller than German ones. Many Italians in their 20s and 30s live at home with their extended families, which means that the transmission of the elderly is great, and when critical care units were oversaturated, so were the deaths. This is less common in Germany, where many nursing homes have also adopted a strict isolation regime. In Germany, Heman says, "they did a better job of protecting the elderly." Some estimates suggest that only 20% of cases of covid 19 in Germans were over 60 years of age, compared with more than 90% in Italy.

The UK, which has seen the second highest mortality rate of covid-19 after Spain, does not care about its elderly - deciding at some point to release hospital patients to return to nursing homes without testing them for this disease. The advice of the government of 1.5 million citizens in the UK with basic health conditions to isolate themselves three months from the end of March may have helped protect those people, but for Gupta the high mortality rate in the UK reflects a deeper problem - years of erosion of community support services that provide pastoral care. "There's just not enough investment in hospitals and that general practitioner or other first-rate person advising a vulnerable person," she said.

Holding on to her prediction, she believes quarantine is oversaturation and that the care and protection of the front line of the vulnerable - which should have been a priority from the beginning - should now be given priority. She also believes that the worst is behind them and that although the next waves cannot be ruled out, they will probably be less bad than what they have experienced so far. The disease will turn into an endemic imbalance, in her view, perhaps every winter returning like a seasonal flu.