One of the great unknowns surrounding the SARS-CoV-2 coronavirus is knowing whether, after overcoming the disease, it is possible to become infected again. It is not yet well known what this immunity is like or for how long it protects us, but little by little some indications are emerging in this regard.
A few weeks ago the alarm was going off: several people from South Korea who had overcome COVID-19 again tested positive. The news caused great concern, because many policies related to the management of the pandemic and the prevention of new outbreaks are based on the role of the immune system. However, a few days ago a newspaper in the Asian country echoed a large study that would confirm that it was false positives, and that in reality these people would not have been infected again.
The explanation lies in the fact that the PCRs identify the genetic material of the virus, but they are not able to differentiate if it is alive or dead, so it is very likely that it was virus remains, but it would not be active and therefore these people would not contagious.
They are not contagious but… are they immune?
The news is reassuring, but it says nothing about acquired immunity: do patients who have overcome the disease produce enough antibodies to be protected against a flare-up? And, in that case, how long does that immunity last?
A study just published in the journal Immunity indicates that most discharged people produce antibodies and T-type cells specific to the virus, but responses vary between patients. The results obtained from some of the people evaluated two weeks after discharge suggest that these antibodies would remain for at least that period of time. On the other hand, this work indicates which parts of the virus are most effective in triggering these immune responses and could be the target of potential vaccines.
Antibody production
Specifically, all the patients studied showed higher levels of immunoglobulins, both IgM –which are produced during the active phase of the disease– and IgG –which are produced later and are maintained in the memory phase -, which to the nucleocapsid protein SARS-CoV-2, which encapsulates viral genomic RNA, as well as the protein S receptor-binding domain (S-RBD), which binds to receptors on host cells during the process of entry viral. Taken together, these findings show that COVID-19 patients can develop immune responses to SARS-CoV-2 proteins and suggest that these antibodies would persist for at least two weeks after discharge.
Possible targets for vaccines
On the other hand, the results indicate that the amount of neutralizing antibodies was positively associated with IgG antibodies against the protein S receptor binding domain, but not with those that bind to the nucleocapsid protein. Additionally, S-RBD induced antibody and T cell responses. “Our results suggest that S-RBD is a promising target for SARS-CoV-2 vaccines,” says Fang Chen, researcher at Chui Yang Liu Hospital, affiliated with Tsinghua University (China) and co-author of the study. “But our findings need further confirmation in a large cohort of COVID-19 patients.”
