With coronavirus cases and the infection rate skyrocketing, it's clear that Israel, like other countries, no longer has the ability to keep a further wave in check, and that the omicron variant will soon sweep over the country. In that situation, the question is whether this contagious variant will produce a natural herd immunity, a term that cropped up again after two years of the pandemic.
As a rule, herd immunity is achieved when a large proportion of a population is exposed to a virus or vaccine and develops immunity at a level which limits the ability of the virus to spread. Subsequently, even those who have not been exposed or vaccinated are protected from infection or illness, and it eventually peters out.
In relation to the coronavirus, two possibilities of reaching herd immunity were discussed: natural immunity following massive infections, which would create a collective envelope of protection and therefore shrink the pandemic. However, most experts rejected this possibility out of hand due to the heavy cost in serious illness and mortality, with no ability to control the rate of infections.
The second possibility, immunity after vaccination, became a real prospect with the development of vaccines against the virus. Thus, high rates of vaccination in Israel against other infectious viral diseases, such as polio and measles, prevent their outbreak and protect the public. Even though Israel was the first to vaccinate its citizens against the coronavirus, it did not reach herd immunity due to lower rates of vaccination, as well as the ability of the virus to mutate.
The fact that the omicron variant is considered less virulent than earlier variants raises the possibility that massive infections with this variant, with vulnerable populations relatively protected, may allow Israel to finally take control of the pandemic. The person in charge of battling corona, Prof. Salman Zarka, sounded skeptical about such a possibility. “We have no policy of [deliberately induced] mass infections,” he said. “Protect yourselves against getting infected. We don’t know enough about omicron. Herd immunity has no scientific basis and I don’t know if getting omicron will afford protection.”
The issue of herd immunity will be resolved soon, even if striving for it is not an official policy. It’s likely that within weeks, millions of Israelis will be infected with the virus. They will join millions of others whose immune system recognizes the virus to some extent, whether following vaccination or through infection.
According to many experts, this question is as complex as the virus itself, but the answer may be positive. Alongside the cautious estimates, there is a series of asterisks to also consider: If immunity is achieved, what is the level of immunity and for how long does it last? What are the characteristics of the immune herd? Does it include people infected with or recovering from only the omicron variant? Is it sufficient to get infected once or is a “booster” required? Regarding veteran and familiar viruses, science and the medical literature provide clear answers. When it comes to the coronavirus, the knowledge gaps are glaring.
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Experts: Vaccine preferable to natural herd immunity
“The omicron wave can produce herd immunity, but it’s hard or impossible to predict how stable it will be over time,” says Dr. Adi Stern from Tel Aviv University, who studies the coronavirus genome.
“The key question is the cost of creating this immunity, in terms of the number of people hospitalized, the number of seriously ill patients and the mortality rates, as well as the long-COVID phenomenon, which we are far from completely understanding. Thus, there is no doubt that immunity through vaccination, with its safety confirmed, is preferable to immunity based on a ‘vaccination’ that is based on a virus running wild in your body and in the population, uncontrolled.”
Dr. Oren Kobiler from the department of microbiology and clinical immunology at the faculty of medicine at Tel Aviv University adds: “Immunity is a relative concept. The omicron wave will subside due to herd immunity, since we’re taking no other actions to prevent it. The thing is, no one knows how long this protection will last, and at what level, if at all, it will provide immunity against other variants. Beyond that, we don’t know to what extent serious illness activates the immune system and what protection it leaves behind. The advantage of vaccination is the uniformity of the reaction. I’m not certain that omicron only causes a mild disease, or that there aren’t later effects following infection. In my view, vaccination and prevention of illness through restrictions is still the safest approach.”
Prof. Eran Segal from the Weizmann Institute, who advises the cabinet on COVID policy, says that “of course we don’t yet know how herd immunity works and what rates of infections and immunized people are required, but we can surmise that omicron will create some kind of herd immunity here and overseas, and that anyone who’s infected will be more protected against infection by other variants. Nevertheless, it’s important to note that it’s better to get vaccinated and not wait to get infected, since the illness is expected to pass quicker that way.”
Segal adds that “there could definitely be further variants in the future which will breach the protection against omicron, just like it breached the protection against the delta variant.”
Crossing the threshold
In the first months of the pandemic, there were estimates regarding the threshold for achieving herd immunity. Some experts talked about 70 percent, others quoting higher levels of people needing to get infected. Over time, with the appearance of the variants, it turned out that its range of mutation is broader than was expected. The more the mutations drove the virus further from the version on which the vaccine was based, the version which caused the first infections, the lower the immune protection, which was based on the original virus’s attachment to cells. This is before considering the waning of antibody numbers over time following an infection.
Thus, the basic logic of herd immunity which requires reaching a certain rate of immunity in a population, is unlikely in this case. It may still be possible to achieve immunity, but not in the way one can hope for in other cases. “People think that herd immunity means that the virus almost disappears, as is the case with polio, smallpox or other childhood diseases,” says the head of the laboratory for immunotherapy at Bar-Ilan University, Prof. Cyrille Cohen. “I don’t think herd immunity will be achieved with coronavirus. If some kind of immunity is achieved, I believe it will be like flu. The virus will continue to be here, but since most people will be among those exposed to it, the illness will be mild and the virus will find it difficult to spread and paralyze the health system.”
Cohen believes that the relative stability will be disrupted from time to time: “It should be remembered that variants will continue to appear, and some may be significant, so we are likely to see occasional waves of increased morbidity, while vaccines will continue to reduce the risk of serious illness and complications.”
Dr. Dvir Aran, head of the Biomedical Data Science Laboratory at the Technion, believes that the concept of striving for herd immunity is fundamentally wrong, and stems from a misinterpretation of the data in Israel and around the world. “It is quite clear that Israel is heading in the direction of removing all effective containment measures in favor of herd immunity,” he said.”This is taking a big risk based on the belief that there will not be many hospitalizations or long-term effects — but these two assumptions still require proof. There is no way to know the long-term effects of omicron after only five weeks. It has very strong attachment capabilities. It may bind less to lung cells, but it does bind to other cells. We just don’t know.”
Aran believes that predictions about the extent of the virus’ spread are also a kind of risk since they ignore changes in public behavior in the face of the threat: “I think there will be more infections than in previous waves, but less than one would think,” he said. “I think it was possible to lower the rate of infection with the tools we used and continue to vaccinate. By March there should already be a vaccine for the omicron variant. I think that at the end of this wave we will also find ourselves with many hospitalized people – more so than the delta wave, because we removed all defenses – and did so without herd immunity.”