Status: 03/26/2022 3:12 p.m
For a long time, herd immunity was considered the way out of the pandemic. In the meantime, this hope has evaporated among many experts. Who is it?
The head of the Robert Koch Institute Lothar Wieler removed the word herd immunity from his vocabulary in relation to Covid-19 back in November. The virus will not disappear completely, he said at a federal press conference.
Herd immunity means that a large part of the population is immune to a pathogen, so that the chains of infection break off early. This protects non-immune people from infection. Andreas Scheuch, aerosol researcher and physicist, shares Wieler’s assessment: Herd immunity cannot be achieved with the currently approved vaccines.
In the case of Covid-19, the individual protection against a serious illness through vaccination is very high – around 93 percent. However, the protection against infection with Omikron is significantly lower – the vaccines do not produce sterile immunity. This means that they create an immune system that prevents the disease, but this is often not enough to completely eliminate the virus. Even if a vaccinated person shows no symptoms, they can pass the virus on to others.
Virus can jump from animals to humans
According to aerosol researcher Scheuch, the virus can also survive in other species and then jump back to humans. Studies also confirm these assessments Denmark and the Netherlandswho studied the transmission of the virus from mink to humans on farms. The researchers came to the conclusion that there was a high probability that employees would have contracted the animals. This property of the virus makes it virtually impossible to achieve herd protection.
Reinhold Förster, Vice President of the German Society for Immunology, does not currently believe in community protection either: “A person who is not vaccinated and is only surrounded by vaccinated people is not protected at all because the vaccinated people can still be carriers of the virus .”
This is one of the reasons why, for immunologist Förster, the way out of the pandemic does not currently mean herd immunity. He is counting on the population gradually building up several layers of immunity through repeated contact with the virus: It is quite possible that people who were already ill with the omicron variant in December will become infected again in April. But that is not so bad, since a certain basic protection already exists. This mechanism is gradually helping to normalize the situation, explains Förster.
Herd protection or herd immunity?
Martina Prelog, immunologist and specialist in pediatric and adolescent medicine from the University Hospital Würzburg, has a different view of the issue of herd immunity. She points out that the term herd immunity can have different meanings. Many understand the term today from the perspective of epidemiology. There, the understanding relates more to the term herd protection, so the effectthat a sufficient number of individuals in a group are immune and thus also protect non-immune individuals from infection.
In contrast, Prelog explains, for immunologists, herd immunity means how many individuals in a group are immune. In this sense, a sufficiently high herd immunity, i.e. a sufficiently high proportion of immune people, so as not to overload the health system, for example, is quite achievable. However, this still means that non-immune people can become infected with the virus.
The decisive factors for this type of herd immunity are how many people have been vaccinated or recovered and how long the protection lasts after vaccination or infection.
In a study, Prelog is with other researchers concluded that a person would need to come into contact with the virus three times in order to have enough neutralizing antibodies to be adequately protected against omicron as well. How long the protection will last after three contacts – either through vaccination or illness – is still difficult to estimate, “but probably at least six to twelve months based on current studies, if not longer,” says Prelog.
Therefore, a high vaccination rate is still important
Regardless of the exact definition of herd immunity, Prelog and Förster agree: on the way out of the pandemic, a high vaccination rate is still very important. A comparison of the current corona situation in China’s Hong Kong Special Administrative Region and in New Zealand shows how important it is.
The no-Covid strategy has long applied in both New Zealand and Hong Kong. There have been very few corona cases there in the last two years. From mid-February onwards, the incidences in both regions rose at a similar rate, but the death rate differed significantly.
While this is around two people per million inhabitants in New Zealand (as of March 22, 2022), Hong Kong recorded the highest death rate in mid-March that has been measured worldwide since the beginning of the pandemic: almost 38 deaths per million inhabitants were registered. The difference between the two regions: the vaccination rate. In Hong Kong, 88 percent of the deceased were not fully vaccinated (as of March 18). Skepticism about vaccination is particularly high in the older population groups – not even 40 percent of people over 80 have been vaccinated at least twice (as of March 22, 2022). For comparison: in New Zealand it is a good 98 percent.
These figures support the assessment of Prelog and Förster: the individual protection against severe courses is still very high after triple vaccination, even with the omicron variant. However, people who have not yet been vaccinated or have recovered cannot currently be indirectly protected – even with a high vaccination rate.