Herd immunity is an important condition to stop any epidemic, including the coronavirus pandemic. Let’s check how Zaborona explains how it works and why vaccination is a key condition for collective immunity.
What is herd immunity?
This is the phenomenon when the majority of the population is not susceptible to infections and viruses and, in turn, it protects the other part that is vulnerable to them.
‘Herd immunity’, also known as ‘population immunity’, is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection. WHO supports achieving ‘herd immunity’ through vaccination, not by allowing a disease to spread through any segment of the population, as this would result in unnecessary cases and deaths.
Herd immunity against COVID-19 should be achieved by protecting people through vaccination, not by exposing them to the pathogen that causes the disease. Read the Director-General’s 12 October media briefing speech for more detail.
The formed herd immunity strongly slows down the spread of diseases. For example, if previously 100% of people were potential carriers of the virus, then when the collective immunity is developed – more than half of them will be immune and, therefore, will not be able to infect others. Actually, if the majority acquires immunity, not only these people but the rest of the population is protected.
Depending on how contagious the disease is, 50% to 90% of the population needs immunity before the incidence rate begins to decline. For example, measles is a highly contagious disease: 94% of the population must be immune to break the chain of transmission.
People who are immune to a virus or infection act as a barrier to the spread of the disease. Moreover, immunity can be acquired both naturally – if you are already sick and the body has worked off the antibodies, and artificially, i.e. due to vaccination.
Herd immunity will work perfectly if the pathogen doesn’t evolve to evade the immune response, and if there are no other vectors than humans.
Why is it needed at all?
The fact is that there are people who cannot develop immunity after vaccination, or they are simply forbidden to vaccinate on medical grounds. You can’t give many vaccines to babies. Vaccination is also contraindicated in patients with HIV / AIDS, lymphoma, leukemia, bone marrow cancer, as well as those who have recently undergone chemotherapy or radiation therapy. At the same time, the vaccine may not work for some people. For all these people, herd immunity is the only way to avoid infection or virus.
A high level of immunity in one age group can create a herd immunity for other age groups: the younger population can protect the elderly and vice versa – older people can protect infants. For example, vaccination of adults against pertussis reduces the incidence in children.
Is it possible to completely eradicate the disease in this way?
Yes! But for the virus / infection to finally disappear, collective immunity must persist in society for some time, at the same time around the world. If under these conditions the spread of the disease completely stops, the number of patients will decline – when it reaches zero, the disease is considered eradicated.
Among the benefits of disease eradication are, firstly, the absence of human casualties, and secondly, the saving of the finances of entire countries, as well as the ability to use resources allocated to counter the virus for other purposes.
Thanks to collective immunity and vaccination, humanity has already defeated the plague of cattle and smallpox. Due to the lack of trust in modern medicine, the world still cannot overcome polio, although most countries make a lot of efforts to do so.
But why do people still get measles?
Because in some regions, people are still poorly vaccinated. In 2020, measles was declared overcome. However, for example, in 2019, 1,282 cases of the disease were detected in the United States. Most often, these outbreaks occur through tourists: by visiting places where the population has not been vaccinated against measles at all, they transmit the disease to people who, for example, are contraindicated or simply refused vaccination. At the same time, there are cases when the period of immunity after the vaccine ended or people did not receive all the required doses.
How exactly can it be achieved?
Here everything is simple: get vaccinated. The more people in society who receive the vaccine and develop immunity to the virus, the less likely they are to become infected. However, immunity can be acquired after the disease – as a result of the formation of antibodies.
This happened in the Brazilian city of Manaus, which during May – October 2020 was severely affected by the coronavirus. Immunologists have predicted that by June 2020, the number of people infected with the coronavirus will exceed 60% – thus creating a herd immunity in the region. Suddenly, however, a new immune-resistant strain of the coronavirus appeared in the country and infected many people in the city.
If I don’t want to get vaccinated, will herd immunity protect me?
It will totally depend on what percentage of the population is vaccinated. Those who refuse vaccination due to ideological or religious beliefs, superstitions, informational influences, etc., contribute to the fact that there will not be enough vaccinated people to form a collective immunity. Simply put, by giving up the vaccine for no apparent reason, you are harming those who cannot get the vaccine for medical reasons.
At the same time, it’s almost impossible to convince a person who is convinced of the harm of vaccination if the percentage of vaccinated in society is too low – a vicious circle emerges. People who share the same views and do not want to be vaccinated often live in the same area, go to the same school or attend the same religious services, resulting in potentially large groups of unvaccinated people who are close to each other.
What is required for collective immunity to COVID-19?
According to various estimates, 60-70% of the population needs to be immune. To achieve this, many people around the world need to be vaccinated. However, some researchers believe that in the case of COVID-19, collective immunity will never be achieved. Analyst Yuyang Gu changed the name of his COVID-19 prediction model from “Path to Collective Immunity” to “Path to Normalization.” He said that reaching the threshold of collective immunity is unlikely, in particular, due to indecision about vaccination and the emergence of new strains. His opinion is also shared by epidemiologists and scientists.
First, it is still unknown whether available vaccines protect against the symptoms of the disease or completely block the possibility of disease or transmission of the virus. Collective immunity requires that the virus not be able to spread. Second, as new strains of the coronavirus emerge, it becomes even more difficult to control their spread because no one knows exactly how they are transmitted and whether the vaccines work on them. At the same time, antibodies formed after the disease do not protect the body from new strains.
However, even without collective immunity, vaccination of people vulnerable to the virus reduces the number of hospitalizations and deaths from COVID-19. The disease may not go away any time soon, but its prevalence is likely to decrease.
If everything is bad, then does it make sense to get vaccinated?
Yes. First, you protect yourself from the severe symptomatic course of the coronavirus. Secondly, the above-mentioned problems indicate that it will most likely not be possible to completely overcome this disease worldwide. However, if enough people living in the same area get vaccinated, it will protect vulnerable people who cannot be vaccinated.
