Seroprevalence of anti-SARS-CoV-2 antibodies

SARS-CoV-2 infection causes a wide variety of disease symptoms, ranging from fever, asthenia or myalgia to pneumonia and, in most severe cases, respiratory distress syndrome acute called COVID-19. Yet a large number of patients infected with SARS-CoV-2 remain asymptomatic. SARS-CoV-2 spread rapidly around the world and was declared a global pandemic in March 2020.

It remains an ongoing threat to health and socio-economic well-being. Despite the global number of infections reaching tens of millions, including nearly one million deaths, due to mitigation measures, the overall infection rate is relatively low with local infection hotspots. Although scientific progress is rapid, there remains a pressing need to understand the immune response following SARS-CoV-2 infection, including its role during disease and especially its potential long-term protective effects.

A prime immune target during coronavirus infections is the Spike(S) protein, which is closely associated and targeted by neutralizing antibody responses and protective immunity, unlike most other viral proteins [1-4]. The S protein is responsible for the interaction of SARS-CoV-2 with host cells via ACE2 binding [5-7]. It can be divided into two regions, S1 and S2. The extraviral S1 region contains in its second domain the receptor binding domain (RBD) [8]. The SARS-CoV-2 RBD sequence shows limited homology with seasonal coronaviruses or EMC/2012, the cause of Middle East respiratory syndrome (MERS). In contrast, the SARS-CoV-2 RBD shares 73% of its sequence with the SARS RBD [3].

Attempts to reduce and control the SARS-CoV-2 virus rely on increasing interpersonal distance, including the closure of much social and economic activity, as well as testing for acute infection and personal hygiene measures. This was implemented at the start of the epidemic, with the University of Lisbon closing after March 13, 10 days after the first cases were recorded in Portugal. However, during the transition phase that followed, restrictions were steadily lifted.

The gradual return to social and economic activity requires active surveillance to determine local outbreaks, contact tracing and quarantine. In addition, those most vulnerable to COVID-19 will need to remain under enhanced protection. Important information is how protective immunity develops in the general population and in specific groups such as healthcare professionals. A thorough assessment of the duration of protective immunity is essential to determine what steps to take to prevent and manage future waves of SARS-CoV-2.

This information will need to be collected widely, in different locations around the world, reflecting local conditions, such as containment measures and their timing. The data obtained must be precise and the methods used transparent and reproducible to allow comparisons between places and countries. The recent SARS-CoV-2 outbreak brings limitations with respect to exposure time, but also gives us the opportunity to acquire real-time data and develop reliable longitudinal follow-up studies.

To determine the cumulative rate of infection in communities and gain insight into potential protection against reinfection, serological testing is essential. Depending on the objectives of the study, the setup of such assays can be used for detection of SARS-CoV-2 exposure as well as to better understand neutralization activity, as titers of antibodies for protein S and RBD correlated well with neutralizing activity [3, 9–11]. We describe the detailed setup and versatility of a seroconversion test for determining humoral immunity to SARS-CoV-2 that has been used for screening hospitalized patients, post-COVID-19 healthy volunteers, and hospital staff.

University of Lisbon. We report that in the acute phase, males produce more antibodies than females, but levels balance out during the resolution phase and are similar between sexes in the months following SARS-CoV-2 infection. . We show that antibodies against SARS-CoV-2 Spike and its RBD domain are easily detectable in the majority of cases, including in patients receiving immunosuppressive or antiretroviral therapy. Consistent with a classic immune response, anti-SARS-CoV-2 antibodies in the blood peak around week 3 post-infection, and although antibody titers decline, IgG antibodies remain.