How many antibodies do you need to be reliably protected from coronavirus

Is it possible not to be afraid of contracting coronavirus after vaccination? An antibody test helps to understand this, reports DW... But there are two problems. The first - with antibodies, a lot is still unclear. The second is the delta strain.

A person who has been ill or vaccinated against cove human antibodies are formed against the spike protein. SARS-CoV-2 uses this protein to bind and enter cells. The spike protein helps antibodies recognize the coronavirus. Covid becomes visible to the immune system. The spike protein sends an impulse to her, prompting an immune response.

The danger of the delta strain

When talking about the effectiveness of mRNA-based vaccines such as BioNTech / Pfizer and Moderna, the scientists assumed that these drugs provide more than 90 percent protection against coronavirus. However, the situation with the delta strain is quite different. Compared to the original SARS-CoV-2, the latter is far more contagious.

The danger of the delta variant is that it infects those who have received the first dose of the vaccine. Immunologist Carsten Watzl of the Leibniz Institute at the University of Dortmund believes that the effectiveness of the BioNTech / Pfizer vaccine has thus decreased. This vaccine protected from the original strain by 90 percent. Now its efficiency has dropped to 88 percent. At the same time, the effectiveness of the AstraZeneca vector vaccine dropped from 66 percent to 60 percent.

According to data from Israel, protection against infection with a dangerous variant of the coronavirus, even with the BioNTech / Pfizer vaccination, does not exceed 64 percent. However, the vaccine still protects 93 percent against severe disease. The Israeli Ministry of Health is currently considering a third dose of BioNTech / Pfizer.

There are more questions than answers

The delta option once again presents scientists with a serious challenge. Many of us are immune to the currently known covid strains even after the first dose of the vaccine.

But this is not the case for all vaccinated people, says Karsten Watzl. The vaccine alone does not guarantee immunity, he said. The decisive factor is the development of sufficient immunity by our body. “But it’s impossible to measure at the moment,” added Watzl.

For example, with inoculation from tetanus, the situation is different: vaccination titers can be determined in the laboratory by passing a blood test. If the number of antibodies exceeds a certain threshold, it means that the person is immune to the tetanus virus. If the titer is too low, re-vaccination is necessary.

“In the case of the coronavirus, we have not yet reached this stage,” says Watzl. According to him, it is not yet known what exactly needs to be measured in order to determine whether a person really has immunity. He believes that neutralizing antibodies play a decisive role. They bind the virus, making it impossible for it to infect cells. “But how high the number should be is still unclear,” says Watzl.

Role of T cells in protecting the body from covid

Antibodies are not the only thing that matters in fighting infection. The virus can multiply as soon as it enters the cells, but antibodies cannot get there. That's what we need T cells for, Watzl said. They are capable of killing cells infected with the virus. The body will destroy several cells infected with the virus and thus allow the virus to spread further.

Today doctors can measure both neutralizing antibody titer and T-cell count. The last test is relatively difficult but rewarding. “By itself, the number of antibodies does not always indicate how well a person is protected. It may well be that he has almost no antibodies, in other words, he may be infected with a virus. But his T-cell response is so strong that he doesn't get seriously ill, ”says the immunologist.

“So people with high antibody levels are most likely well protected from the coronavirus,” Watzl says. However, the inverse conclusion that a small number of antibodies means lack of protection is most likely not true.

Threshold question

Anti-covid antibodies are measured using a variety of methods. Laboratory tests have clear standards that range from a minimum value to a maximum value. The results allow you to see if the indicators are within the normal range. But in the case of the coronavirus, these standards have yet to be defined.

“The number of antibodies ranges from less than a hundred to several thousand units. If the number is in the upper third or even the upper half of the spectrum, the person probably has a good immune defense... But doctors cannot yet name the exact threshold value, ”explains Watzl. It is also still not known exactly how quickly the antibody level decreases. It is only known that their number decreases over time.

The immunologist says that the decrease in the number of antibodies occurs in two stages. The highest antibody level is immediately after vaccination. A relatively rapid decline is observed in the first few months after vaccination. However, at some point, the level of antibodies reaches a certain value, and from that moment on, it decreases very slowly. “We know this from other vaccinations, and it seems to be the same with the coronavirus,” Watzl says. However, this has not yet been scientifically proven.

Nothing is known

In some people, antibodies do not form even after being vaccinated twice - or they do not form very much. These people seem to be not protected properly, says Watzl.

There are many factors due to which antibodies are produced at low levels. Age is one factor. Another factor is a suppressed immune system, which doesn't work the way it does in healthy people. Such an immune system cannot adequately resist the virus in the body. Often a third vaccination is needed for a person to form antibodies.

In other words, there are still more questions than answers, and it is still not possible to figure out how antibodies really work. Options range from “many antibodies and good protection” to “too few antibodies and poor protection” and “few antibodies and still sufficient protection”.

At the moment we have the following conclusion: nothing is known for sure. But immunologist Watzl is optimistic: “So far, it is really unclear where the threshold value is and at what level a person is really protected. But we will definitely find out. ”