Herd immunity as protection against corona – does that work?
Being healthy and staying healthy – that’s what everyone wants, not just in times of the SARS-CoV-2 coronavirus , which is currently going around the world. Every single person can do a lot for their own health. In addition, everyone can also make a contribution to the health of society, for example when it comes to protection against infectious diseases. We are talking about so-called herd immunity. Vaccination plays an important role in this context. The more people protect themselves from a disease by vaccination, the lower the risk of other unvaccinated people becoming infected. But what exactly does herd immunity mean? And what role does it play in connection with the coronavirus and the resulting disease COVID-19? You can find out more about this here.
Definition of herd immunity – what is it?
According to the current definition, herd immunity means that an entire population group, figuratively speaking the herd, is protected from a contagious disease because a large proportion of this group is immune to it – either through a previous infection or a vaccination. The pathogen can no longer find anyone to infect and the disease cannot spread further. This creates protection even for those members of the group who are not immune themselves.
Herd protection or the herd effect is also often mentioned.
How does herd immunity work?
Highly contagious infectious diseases can spread quickly, so that a large number of people become ill within a short period of time. A good example of this is measles, which is still common today, especially in developing countries, and can sometimes be fatal. The number of infections in Germany has been greatly reduced through the consistent implementation of measles vaccinations over the past forty years.
If a population reaches a vaccination rate of more than 95 percent, then not only the vaccinated people are protected from infection with measles , but also the people who are not vaccinated. This can include:
- unvaccinated babies up to one year old
- People with an immune disease who cannot be vaccinated
- People who have not previously been vaccinated for other reasons
When the threshold is reached, so-called herd immunity occurs. The explanation for this is that vaccinated people do not transmit the disease, infection occurs less frequently and the disease spreads much more slowly or not at all. At best, this can lead to the eradication of an infectious disease, such as polio in Europe. In order to achieve this goal in the case of measles, compulsory vaccination against measles was introduced in Germany in March 2020.
Why is herd immunity important?
In every population group there are people who are too old, too young, too ill or immunocompromised to vaccinate themselves. However, it is precisely for these groups that infection with an infectious disease is usually particularly dangerous. Here, the willingness to vaccinate every single healthy person and the resulting community benefit, herd immunity, is particularly important and of great importance.
Incidentally, the principle of herd immunity does not work if a disease is not only transmitted from person to person, but (also) by animals, for example in the case of rabies or TBE . In this case, only the vaccination of individuals can offer adequate protection.
Is herd immunity possible without vaccination?
Not only vaccinations, but also infections can in certain cases lead to herd immunity and protect against infection. The prerequisites for this are the following:
- The immune system learns from the infection and becomes immune to precisely that infection.
- A large part of the population has to be infected and go through the disease.
The risk is obvious: if the disease is serious, there is a risk that many people may die from it as it progresses.
Therefore, preventive vaccination is considered by experts to be the gentler way to achieve immunity. In contrast to living through the respective infectious disease, which can be associated with an incalculable course or long-term effects, the side effects of vaccinations are considered to be quite minor – serious side effects are extremely rare. Because with a vaccination, the immune system is trained, for example by administering weakened or killed pathogens (active vaccination) or by administering antibodies against the respective pathogen (passive vaccination), to recognize and fight this pathogen in the event of an infection.
Herd immunity in corona infection?
A pandemic , such as the current corona pandemic, could theoretically also lead to natural herd immunity: people infected with the virus remain contagious for some time, then recover, become healthy and are then immune to another coronavirus for an as yet unknown period of time -Infection. The more people who have contracted the disease COVID-19, the sooner herd immunity against the coronavirus will be achieved. This is the theoretical ideal case.
When herd immunity kicks in also depends on how contagious a disease is. Experts initially assumed that 60 or 70 percent of the population would have to be immune to the corona virus in order to stop the uncontrolled spread of the pandemic. After that, infections would still occur, but less frequently.
More recent calculations assume a required immunity of 80 percent . The reason for this is, among other things, the increased number of reproductions as a result of the mutations . The delta variant of the virus in particular is also considered to be particularly contagious and can reduce immune protection through vaccinations or previous infections, so that some recent studies even assume a required vaccination rate of 90 percent .
Experts strongly warn against the strategy of achieving herd immunity through natural “infection” of the population, as some countries – including Great Britain – initially tried to do: Until a disease with a high mortality rate – Corona is assumed to be 0.7 up to 7 percent – if herd immunity occurs, many deaths would have to be expected. For comparison, it is estimated that the annual flu epidemic has a mortality rate of 0.1 to 0.2 percent. Even those who survive the infection must expect long-term consequences.
In addition, due to the simultaneous occurrence of numerous cases of infection, the healthcare system is exposed to an enormous burden, which means that if the number of infections is too high, the care of the infected, but also of other people in need of treatment, could no longer be guaranteed.
COVID-19: herd immunity through vaccination?
In the case of COVID-19, vaccination is also an effective way to protect yourself from serious illnesses. But are vaccinations capable of providing herd immunity that protects the unvaccinated? There are now some arguments against it.
Because it is still unclear how long the immunity lasts after an infection with SARS-CoV-2 or a vaccination. The first cases soon became known in which people were infected with the corona virus a second time. It is now assumed that regular booster vaccinations will probably be necessary due to the decreasing immunity. That makes achieving herd immunity at least more difficult.
Also, a requirement of herd immunity is that immune people cannot infect others. Even if infection is at least less likely, it is still possible. As good as the vaccinations make severe courses less likely – they do not offer 100% protection – neither for others nor for the vaccinated themselves.
Add to this the emergence of new viral mutations that may be more contagious, which in turn increases the required immunity rate for eventual herd immunity. They can also make herd immunity more difficult if they reduce the protective effect of existing antibodies.
It should also be considered that many population groups cannot be vaccinated at the moment, especially children, but also many people with previous illnesses. Accordingly, the proportion of vaccinated people in the rest of the population would have to be all the greater. Calculation models assume more than 85 percent. This in turn requires a corresponding willingness to be vaccinated.
This shows that complete protection through herd immunity is rather unlikely in the case of SARS-CoV-2. However, this does not mean that the protective effect for individual vaccinated persons is not given. In addition, a high immunity rate always helps to slow down the spread of the virus, relieve intensive care units and reduce the risk for unvaccinated people. It is therefore best if as many people as possible are vaccinated against COVID-19 in order to prevent a serious course of the disease.
In addition, the virus can only be contained if everyone consistently follows the recommended rules. These behaviors not only protect against one’s own infection. They should also cause the corona virus to spread more slowly. This means that the healthcare system can be maintained and sick people can continue to receive appropriate medical care in the future.
