2020-06-04T08: 00
2020-06-04T14: 42
https://ria.ru/20200604/1572424750.html
Scientists find out when the most effective infection protection crashes
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RIA News
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In theory, just
In those years, it was important for the world to defend itself against ailments that killed a large number of children – diphtheria (caused by a bacterium), smallpox, and polio. The idea of herd immunity proved the need for mass vaccination. Vaccinations cause a lifelong immune response in the body, a person will not be able to get sick and transmit the infection. If you vaccinate everyone without exception, the disease will disappear.
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Herd immunity is the only way to restrain the spread of such misfortunes as measles, rubella, and mumps. Observations showed: outbreaks are recorded in populations with a critical number of people immune to these infections – unvaccinated or not ill, for example, in the case of chickenpox.
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In the 1970s, mathematicians proposed a simple model for calculating population immunity. The main parameter is the reproduction index R0showing how many on average one infected person can infect. Suppose the indicator is two, then one infects two, each of them, in turn, two more and so on. But if one in a pair has immunity to infection, on it the chain breaks. How many of these should be in the population in order to avoid an outbreak, calculated by the formula (R0 – 1) / R0. In our example, half.
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The model is getting complicated
Not every vaccine provokes an equally strong immune response; there will certainly be those who have poorly formed defenses or none at all. In such cases, in order for herd immunity to work, it is necessary to immunize more than the calculations show.
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Another problem is the different behavior of people within and between groups, for example, age groups, which affects the rate of infection. Then R0 becomes a complex function, taking approximate values.
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In addition, the default models assume that people are vaccinated at random. If vaccination is targeted, only among risk groups, theoretically, population immunity can be obtained with less effort, as, for example, with seasonal flu. However, this may not work if a large number of infected individuals are concentrated in one place. And then flashes can not be avoided. This happens in the case of measles and poliomyelitis, which have spread in recent years in religious and anti-vaccination communities.
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It is difficult to take into account the “freeloaders” – those who are not vaccinated for various reasons. Many factors influence their decision: there is no money, time, they are afraid of negative consequences. Knowing that collective immunity exists in society, which means that the probability of infection is close to zero, such people expect to ensure their own health at someone else’s expense.
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Coronavirus for a long time
When the epidemic of the new coronavirus began, quarantine was introduced in most countries to contain the infection, smooth out the growth curve of the number of infected people and prevent the healthcare system from drowning from the influx of severe patients.
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In Moscow, the figure is higher – 14 percent, but it can change when the results of testing for antibodies across the country appear.
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