How protected is it from Covid-19?Scientists look for tests to measure immunity

Sobiec checked antibody levels after the second, third and fourth doses of the Moderna Covid-19 vaccine. Each result shows that he exceeds the maximum number of antibodies he can detect in the test, showing a strong immune response.

There is no specific guidance on how to interpret these results to understand the level of protection against infections and illnesses, but Sovieck was reassured that his immune system was playing a role.

“More than 50% of transplant patients do not have a sufficient immune response to protect themselves from the vaccines used by the general public three times instead of two,” said Dr. Dolly Segev, a professor of surgery. I am. New York University Langone Health. “For them [an antibody titer] It’s a particularly compelling indicator of whether you’re protected. ”

Transplant surgeon Segev advocates the use of tests that measure antibodies as a way to check the immune defenses of people with immunodeficiency.

Sobieck says the test results allowed him to make decisions for himself and his family.

“I knew I had an antibody response, so my son was able to go to school directly, which is amazing,” he said. Said.

Correlation of protection

However, measuring antibody levels is one thing. Measuring how much they protect you from Covid-19 is another.

“There is no good correlation for protection, which is a necessary measure to know how well protection is being done,” said Mehul Suthar, a virologist at Emory University.

However, not all antibodies are made the same. Of all the antibodies that the body can make after an infection or vaccination, only a few are considered “neutralizing antibodies”, which means that the infection can be actively prevented.

Tests to measure antibodies are either quantitative or qualitative. Quantitative testing provides up to a certain number of antibodies in the blood, up to a certain point. Qualitative tests only show if a particular antibody is detected. The results of qualitative tests are either positive, negative, or uncertain for neutralizing antibodies.

Peter Gilbert, a professor of vaccines and infectious diseases at the Fred Hutchinson Cancer Research Center and lead author of the Moderna study, states that these correlations can be useful for large groups. For example, scientists can use data from large studies on the correlation between antibody levels in adults and vaccine efficacy to predict vaccine efficacy in children.

However, reaching conclusions based on the antibody level of a single person is far more limited. Gilbert compares individual antibody titers with oil dipsticks in the car.

“Is there less oil in a particular car? So you have to go out and get new oil,” or in this case “get another shot of the vaccine,” he said. “Markers aren’t that good for that purpose.”

This is mainly due to how antibody levels vary from person to person. The correlation of protection also changes over time and is altered by various coronavirus variants. Beyond this, it becomes difficult for scientists to define antibody-level cutoffs that someone can confidently say is protected from Covid-19.

Innate immunity and vaccine-acquired immunity

There are important differences in comparing antibody levels between those vaccinated with Covid-19 and those infected with the coronavirus.

“The response of the vaccine is that everyone who has been vaccinated has high antibodies and can diminish over time …. When infected, it becomes significantly non-uniform. With very low people. Many people have it. Very high antibody response. ”

According to Marion Pepper, an associate professor of immunology at the University of Washington, location is especially important for the immune system.

“There are different immunological environments that make up your body …. If you see an immune response in your arms, you’re a different cast character than if you have an immune response in your lungs,” Pepper said. I am saying.

The immune system is “like many different regions, depending on how an individual is exposed to the coronavirus, whether due to a vaccine injected into the upper arm or an infection of the respiratory system. Each has a different taste. “

Antibodies may help you understand how to compare people with innate immunity to those with adaptive immunity, although they may not provide the best way to know how well someone is protected.

“We know that people with this hybrid immunity are better protected …. So it also says,” Which of these parameters is related to that protection? “Pepper, who leads a laboratory studying hybrid immunity, said.

Observing levels of immune cells and antibodies that change over time in different groups of people will help scientists create vaccines and time vaccines to reproduce the strength of hybrid immunity without actual infection. Helps you learn.

Just a part of the immune puzzle

Antibody levels are just one part of the immune story. There are also T cells, a type of white blood cell that helps fight infection by killing cells infected with the virus or helping B cells, another type of white blood cell, to produce antibodies.

So why do we focus so much on antibodies? “One aspect is that antibodies are probably one of the easiest to measure in the laboratory,” Suthar said.

“I find it much more difficult to go to a T cell-based assay,” he explained. “It’s a little harder to understand how good the T cell response is to this virus, because each individual has a different so-called HLA type.”

Unlike antibodies that are responsible for preventing infection, T cells are responsible for destroying cells that are already infected. T cells can play a major role in vaccine efficacy against more serious diseases caused by more infectious coronavirus variants such as Omicron.

“Memory B cells are B cells that can be reactivated to make antibodies. It generally does not, unless T cells are instructed to go. Therefore, studying T cells understands this immune protection. It will be really important to do, “Pepper said.

However, she said that the complexity of measuring T cells means that no rapid testing is done to measure T cells immediately.

The surge in Omicron indicates that the infection rate may still be high after the vaccine or previous infection. Due to the potential for more variants to form, Covid-19 has become a moving target that requires a constantly evolving understanding of these protection correlations.

“I think the biggest question I have is that everyone else has. What level of antibody is equal to protection from the serious complications of Covid?” Sobieck said.