What amount of antibodies is necessary to have protection against covid?
More and more people have antibodies against SARS-CoV-2, either because they have overcome the infection or because they are vaccinated. And in both cases, despite initial scientific doubts, we now know that the presence of antibodies lasts for more than one year and there are recent immunological studies that make it clear that this immunity can last much longer. This is something that has already happened with some survivors of the first SARS coronavirus, who have maintained antibodies against the original SARS for more than ten years. To answer our readers question, I have to say that what you have to be very clear about is that the presence of antibodies against a virus does not guarantee that we are protected against infection. For the antibodies to protect, they have to be able to disarm the virus, therefore, not just any antibody is valid, they have to be active against the virus, what we call neutralizing antibodies. If we only quantify the amount of antibodies we have, that data will not tell us if they are protective or not. In order to determine if there are protective or neutralizing antibodies, it is necessary to do tests in the laboratory. In these tests, the antibodies are put in contact with SARS-COV-2 or with one of its variants and their ability to prevent the virus from entering a human cell is analyzed. But this technique is time consuming and is generally done in clinical trials, for example to study the efficacy of a vaccine or to see if existing vaccines work just as well against newer variants of the virus. It is not a diagnostic technique that can be used to analyze the quality of a persons immunization, but is used only within the framework of research studies. Furthermore, we still do not know how much neutralizing antibodies is necessary to be fully protected. There are studies in animal models that suggest that it may not take much to achieve this, but more research is needed. Perhaps it is not a question of the amount of antibodies that we have, but of the quality of the response of these antibodies. At this time, the best correlation with protection against infection can be extrapolated if antibodies are detected against the spicule of the virus, and more specifically against the place where the virus binds to its cellular receptor, which is the gateway that uses SARS-CoV-2 to infect a cell. Some survivors of the first SARS coronavirus have maintained antibodies to the original SARS for more than ten years. Another consideration is that the response after infection or immunization may be different in some people. For example, there are people who have compromised immunity, or follow drug treatments that affect their response, or are elderly that compromise the quality of their immune response. I believe that as we vaccinate the world population we will see that there will be groups in which the response will be worse. This means that vaccines will not be as effective for everyone. That is why the clinical trials included people of different ages, to understand how the response would be in all age groups and especially in those most vulnerable. The data that best gives us an idea of how protected people with pre-existing antibodies are comes from reinfection studies and clinical trials of vaccines. Studies of reinfection in hospital workers indicate that having passed COVID-19 reduces the risk of re-infection by 84%, a percentage that increases to 93% for those who initially had a symptomatic infection. In addition, these studies have already taken into account the possible effect that some variants may have, which at the moment do not seem to increase the risk of reinfection, so it seems that protection against the original virus continues to work against these variants. And in the case of clinical trials with vaccines, we already know that all of them confer protection against infection that is above 80%. Therefore, the answer to your question about antibody protection requires a laboratory test to determine whether the antibodies are neutralizing. That said, its also important to know that having antibodies is good news, because if you dont have them, they cant protect you. In other words, this information is already useful, although it is not enough. I know it is frustrating, but a lot of work is currently being done to better address this question and to understand what are the characteristics that confer protection to people. In the case of the reader who writes to us, clinical trials have shown that people who have already had the disease, as she explains in her email, have an 84% less chance of being reinfected. And those are real clinical trials. That is good news, as is the fact that when people are vaccinated they develop more than 80% protection against infection. Those are the objective data. People who have already passed the disease or who are vaccinated are infected in a much lower percentage than the rest of the population. Nuria Izquierdo-Useros She is a doctor in biology, head of the emerging pathogens group at IrsiCaixa. Question sent via email by Maria Jesus Ortega  Coordination and writing: Victoria Toro  We respond is a weekly scientific clinic, sponsored by the Dr. Antoni Esteve Foundation and the program LOral-Unesco For Women in Science, which answers readers questions about science and technology. They are scientists and technologists, partners of AMIT (Association of Women Researchers and Technologists), those that answer those doubts. Send your questions to nosotrasrespondemos@gmail.com or on Twitter #nosotrasrespondemos. 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