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Antibodies are crucial for vaccination to work, but scientists do not yet know what level they need to reach. The new delta variant poses another problem.
After a coronavirus infection or vaccination, the body produces antibodies against the virus spike protein, which SARS-CoV-2 uses to attach to and enter cells. This spike protein allows antibodies to recognize and bind to the virus, making it visible to immune cells.
Scientists previously assumed that people vaccinated with mRNA vaccines such as the one produced by BioNTech-Pfizer had over 90% protection against the virus – but this does not apply to the new delta variant. This variant is much more contagious than the ancestral virus and is spreading all over the world.
ALSO READ: Pfizer, AstraZeneca Vaccine Antibody Levels May Decrease After 2-3 Months: Study
Carsten Watzl, an immunologist at the Leibniz Institute at the Technical University of Dortmund, estimates that the efficacy of BioNTech-Pfizer mRNA vaccines has increased from 90%, in the case of the original virus, to 88% with delta. The efficacy of the AstraZeneca vector vaccine increased from 66% to 60%.
Data from Israel indicate that protection against infection with the dangerous variant is only about 64% when the BioNTech-Pfizer vaccine is used. But the vaccine still offers 93% protection against a severe case of Covid-19. Israel’s health ministry is now considering offering people a third dose of the vaccine.
Measurement difficulties
After two injections, the majority of people are immune to the viral variants known so far – but Carsten Watzl warns that this does not necessarily apply to everyone who is doubly vaccinated.
“Vaccination alone is no guarantee of being immune,” he says, adding that what matters is whether the body has built up sufficient immune protection. “But we can’t measure that right now,” he says.
This is different from a tetanus vaccination, where tests can determine whether a body is sufficiently protected or not. A lab checks the blood for the level of antibody titers. If the number of antibodies exceeds a certain threshold, the person is immune to the tetanus virus. If the titer is too low, the patient needs a reminder.
With the coronavirus, researchers have not yet reached this stage, says Watzl. “We don’t yet know exactly what we need to measure to really determine whether someone is immune or not. Presumably, neutralizing antibodies play a key role – they bind to the virus in such a way that it cannot infect any more. cells. “
But it is not known how high the number of these antibodies must be, he adds.
What do T cells do?
Only antibodies are not essential in the fight against infection. Once the virus enters the cell, the antibodies cannot reach it anymore because they cannot enter the cell. Thus, the virus will replicate itself.
“To combat this, our immune system has T cells; they are able to kill these cells infected with the virus – in other words, we would rather sacrifice a few cells in our body, namely the infected cells, rather than give the virus the chance to multiply, ”says Watzl.
Both of these processes can be measured. In practice, however, it is more difficult to determine the number of T cells than that of antibodies. The T cell test is relatively long but very useful.
“Antibodies alone don’t necessarily tell you how protected you are,” says Watzl: he says that a person may have virtually no antibodies and therefore can still be infected with the virus. “But the T cell response is so strong that the person doesn’t get seriously ill,” he says.
People with a high level of antibodies are probably well protected against the coronavirus, the immunologist added. But the opposite conclusion – that few antibodies mean no protection – is probably not true, he says.
A question of levels
Coronavirus antibody tests use a variety of measurement methods. Normally, laboratory tests use a clear standard stipulating a minimum value to a maximum value. This allows a doctor to see if the levels are within the normal range. The levels have not yet been defined for the coronavirus, however.
So, doctors are getting closer, with measured levels ranging from less than a hundred to several thousand antibodies. “If I’m in the top third or top half, I probably have good immune protection. But I can’t give you the exact cut-offs yet,” says Watzl.
It’s not clear how quickly antibody levels drop, only that they drop over time.
“It moves in two waves – if you look at the levels right after vaccination, you have the highest level of antibodies. In the first few months after vaccination, that level declines relatively quickly. everything settles to a certain value, and only declines very slowly from there, “says Watzl, adding that scientists know about this phenomenon from other vaccinations.” This also appears to be true for the coronavirus vaccine. science just hasn’t proven it yet, ”he says.
More is better
Some people who have been vaccinated twice have virtually no antibodies to the virus, so they are probably not adequately protected, warns Watzl. Low levels of antibodies can be due to age or a weakened immune system. Often, patients need a third vaccination for the body to form antibodies.
Observations range from people who have a lot of antibodies and are well protected, to people who have too few antibodies and are poorly protected, to people with few antibodies who are still protected.
The conclusion so far is that no one knows for sure. But Watzl is optimistic, stressing that “more is better”.
“We don’t yet know what the threshold levels are, and what level it takes to be protected,” he says. “But we’ll get there one day.”
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