Six months after the coronavirus began to spread across the world, there is still little understanding of how the human body responds to the infection. Knowing whether or not a person is immune to Covid-19 after recovering from the disease, and for how long, and why there are some people who do not contract the virus even though they are exposed to it and have no immunity, are some of the main questions immunologists are trying to answer.
Resolving these questions would reveal whether or not it would make sense to create immunity passports for the coronavirus, and shed light on what part of the population is at greatest risk to the SARS-CoV-2 virus.
Manel Juan, the head of the immunology department of the CBD-Clínic Hospital in Barcelona, is one of the researchers trying to solve these issues. This expert is currently coordinating a project between several medical centers in Europe to find out what happens in the immunological system of coronavirus patients when they have an excessive response to the virus (which is one of the ways that Covid-19 kills), and to create more accurate diagnostic tests. In some cases, current tests for Covid-19 fail to detect antibodies even though a person has recovered from the disease, or may even have developed immunity through exposure to other kinds of coronavirus that produce nothing more than cold-like symptoms.
Question. Do the current antibody tests allow us to know if we are immune to a new contagion?
Answer. The determining factor to know whether or not there is immunity are T-cells, which are the ones that offer protection. But the type of test needed to detect them is very complex, takes too long and is not practical. That’s why a test is done with a subrogated marker, which are the antibodies. If you are positive for IgG antibodies [the most common antibody in fighting bacterial and viral infections], we know that there has been a response by T-cells. It’s all connected.
Q. If a person tests positive for Covid-19 antibodies, can they be considered protected? Or does it depend on their antibody levels?
A. Antibody levels are an approximation. It is a mistake to think of them as an absolute figure in a diagnosis. You can have low levels and this may be enough to know that the immune system is working. Saying that if you have more antibodies you will have more immunity, or longer-lasting immunity, is incorrect. Antibodies are not the only element that is immunizing and protecting us in the future. You can have a lot of antibodies yet immunity can last for a shorter period of time, and you can have practically none and it can last a long time. [...] Antibodies are not a real marker of immunity.
We know that patients who have had SARS, which is the most similar to Covid-19, have maintained antibodies for at least one or two years
Q. Does it make sense to create an immunity passport that offers a guarantee that a person is immune?
A. The passport makes sense from the point of view of knowing whether or not a person is immune, but the consequences of using this passport are complex. In the workplace, the existence of this passport could involve discrimination based on the presence or not of antibodies. What’s more, a person with a negative antibody test could also be protected. This is more of a political and social debate, even one for the unions.
Q. Is it possible for a person who tests positive for antibodies to contract the virus again or transmit it?
A. There have been millions of cases in the world and a clear reinfection due to a new entry of the virus once there were antibodies has not been detected. In cases where there was doubt as to whether this had happened, it was demonstrated that it was a reactivation of the same virus, which at that time, the immune system had not been able to eliminate sufficiently for it to not be detected by a PCR lab test. At any rate, among the millions of cases, there may be one who despite having the virus is not able to maintain protective immunity and avoid reinfection.
Q. It’s also been suggested that a person with an asymptomatic infection will have a lower immunological response and could be reinfected, although with a less severe case. Is this something you rule out?
A. It has not been ruled out, but I believe that during the pandemic we have often forgotten the positive data that exists, or we have opted for the most negative possibility if there was still no data. This is not very scientific, although many scientists have argued this way. Researchers need data to affirm that this virus will last a long time or that a specific infection is protective or not. Until this is demonstrated, it is not possible to know. But science is also based on comparisons of similar situations. What we know now is that in patients who have had SARS, which is the most similar thing [to Covid-19] that we know of, even those who have not experienced symptoms, have maintained antibodies for at least one or two years.
A clear reinfection due to a new entry of the virus once there were antibodies has not been detected
Q. Your message is more positive than what is normally heard about the coronavirus.
A. I think that those who have transmitted the most negative version have based their views more on making sure that no one can later tell them “but you said that” than on actual science. Science is centered on the analysis of data, which is very often similar, because you never have 100% of biological figures. But we have enough information on viral infections, even on very similar viruses like SARS, which makes me think the way I do. We have to say that we will never know whether protection lasts one year until a year has passed, but all the data, for now, suggests that this is the case. [Spanish scientist and politician] Eduard Punset used to say that until proven otherwise, he would not die. In the end, he died. Looking around us everyone dies, so the most scientific thing to say is that everyone will die one day. This is similar. In biology, for now, what we know is that those who have antibodies are protected.
Q. If someone tested positive for antibodies two months ago, but negative today, would you say that person has lost their immunity?
A. You have to consider that they are immune, you can’t worry about that. If they have generated IgG antibodies it is because there is a response from T-cells. It is the same thing that happens with vaccines. Vaccines work, although if you look later at the antibodies, you may not have them, but you are still protected, sometimes for five or 10 years. You don’t keep measuring whether your antibody count has dropped. It doesn’t work that way.
English version by Melissa Kitson.