Immune titers of protection against severe acute respiratory syndrome coronavirus 2: are we there yet?

Abstract

A few pieces of research exist about the protective titer against severe acute respiratory syndrome (SARS) coronavirus 2 (CoV-2; SARS-CoV-2) in monkeys and humans in which the protection could be shown as dose-dependent. Early studies supposed that higher levels of pre-existing neutralizing antibodies (Nabs) against SARS-CoV-2 can potentially correlate with the protection to consequent infection. The data so far showed that cellular immunity is as essential as the humoral one. If needed, its presence can be beneficial if the titer of immunoglobulins is not optimal. It is also known that the immune response to the vaccine is similar to the one after natural infection with a production of very high naturalization titers antibodies. However, medical community is still unaware of the immunoglobulin titer needed for protection against the virus. The answers to the questions regarding correlates of protection are yet to be discovered. Still, no studies indicate a specific virus-Nab titer, so one can assume a patient is protected from being infected in the future. The evoked immunological response is indeed encouraging, but a future investigation is needed. Nonetheless, it remains a mystery how long the immunity lasts and whether it will be enough to shield the patients in the long run. Therefore, identifying immune protection correlations, including neutralization titer of antibodies and T cell immune response against SARS-CoV-2, could give a clue. Unfortunately, recent studies in the field have been more controversial than concise, and the data available is far from consensus.