The immune system has numerous ways to protect us from viruses. One of them is the production of specific antibodies against some epitopes of the virus by B-Lymphocytes (Plasmocytes). Some memory B lymphocytes that produce these antibodies can be selected and reserved to defend us in a new attack from the same virus. Another type of defense involves cytotoxic T lymphocytes that destroy cells that are infected, preventing the virus from replicating.
This immunity can be permanent, long-term, that is, it can last for years and it is with this objective that vaccine producers work, trying to obtain this long-term defense response. Unfortunately, this is not always possible, as is the case with HIV. To give a safe response to the population, researchers need to monitor antibody levels for longer to find out. It is also important to monitor whether these antibodies will remain at a low concentration – as is common with viral infections – or whether they will decrease rapidly.
When the researchers followed up on patients with COVID-19 throughout that year, they found that the number of antibodies peaked in the days following the onset of symptoms, and then began to decrease. In several of these patients, the antibodies were virtually undetectable in about three months. To determine how significant this decline can be, researchers still need to know how much antibody is needed to successfully ward off SARS-CoV-2.
If immunity to the virus lasts less than a year, for example, like other circulating human coronaviruses, there may be annual increases in COVID-19 infections until 2025 and beyond. Researchers know little so far about how long immunity against SARS-CoV-2 lasts.
But, as was said at the beginning, antibody production is not the only form of immune protection; memory B and T cells also defend against future encounters with the virus, and little is known so far about their role in SARS-CoV-2 infection. For a clear answer on immunity, researchers will need to follow many people for a long time.
Across the world, epidemiologists are building short- and long-term projections to prepare for and potentially mitigate the spread and impact of SARS-CoV-2. Although their predictions and timelines vary, researches agree on two things: COVID-19 is here to stay and the future depends on many unknowns, including whether people develop lasting immunity to the virus, whether seasonality affects its spread, among other factors.
The results also suggest that there may be some lasting cross-immunity between common flu coronaviruses and SARS-CoV-2. If this really happens, it could explain, in part, the great differences in the severity of COVID-19 symptoms among infected individuals. The researchers try to understand the human immune response to SARS-CoV-2 using animals and cell cultures, along with the latest molecular techniques.
They cataloged antibody and immune cell responses with unusual speed, determined which are probably the most effective, and developed vaccines and therapies that, in animal studies and small human studies, elicit at least short-term immune responses.
But there is no quick and simple experiment that can safely determine whether immunity will be effective or long-lasting. It is too early to know. Memory B cells remain in the bone marrow until the virus returns. But data on the role of memory B cells in driving away COVID-19 is incomplete – cells are more difficult to locate and count than antibodies.
A recent study, which has not yet been peer-reviewed, found memory B cells capable of producing neutralizing antibodies that recognize SARS-CoV-2 in people who recovered from mild COVID-19. Permanent immunity for COVID-19 would be ideal, as it would reduce the risk of people with minimal symptoms spreading the infection so easily.
However, these scenarios are only guessing, because this pandemic has so far not followed the pattern of pandemic flu; we have no precedent to compare with the current pandemic. Even a vaccine providing incomplete protection would help to reduce the severity of the disease and prevent hospitalization.
Still, it will take months to produce and distribute a successful vaccine. In the meantime, we need to keep the innate defenses activated. For this we have the M8 immunomodulator complex. As observed over many years of research, M8 quickly activates macrophages and other defense cells, even without direct contact, but also through the production of small molecules such as nitrous oxide and cytokines.
• For those interested in a more in-depth discussion consult – Nature, Vol 585, 3 September 2020; 23 November 2020; Nature vol586, 653 (2020).
Dorly de Freitas Buchi