Kinetics and persistence of cellular and humoral immune responses to SARS-CoV-2 vaccine in healthcare workers with or without prior COVID-19.

SARS-CoV-2 vaccines are highly efficient against severe forms of the disease, hospitalization and death. Nevertheless, insufficient protection against several circulating viral variants might suggest waning immunity and the need for an additional vaccine dose. We conducted a longitudinal study on the kinetics and persistence of immune responses in healthcare workers vaccinated with two doses of BNT162b2 mRNA vaccine with or without prior SARS-CoV-2 infection. No new infections were diagnosed during follow-up. At 6 months, post-vaccination or post-infection, despite a downward trend in the level of anti-S IgG antibodies, the neutralizing activity does not decrease significantly, remaining higher than 75% (85.14% for subjects with natural infection, 88.82% for vaccinated after prior infection and 78.37% for vaccinated only). In a live-virus neutralization assay, the highest neutralization titres were present at baseline and at 6 months follow-up in persons vaccinated after prior infection. Anti-S IgA levels showed a significant descending trend in vaccinated subjects (p < 0.05) after 14 weeks. Cellular immune responses are present even in vaccinated participants with declining antibody levels (index ratio 1.1-3) or low neutralizing activity (30%-40%) at 6 months, although with lower T-cell stimulation index (p = 0.046) and IFN-γ secretion (p = 0.0007) compared to those with preserved humoral responses.

Targets and assay types for COVID-19 diagnosis.

The lack of complete information on the immune response dynamics to infection with severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) has led to the use of mainly molecular tests such as reverse transcription PCR (RT-PCR) to diagnose Coronavirus 2019 disease (COVID-19). Although remarkable progress has been made in developing effective RT-PCR kits, the lack of specific equipment required to perform this technique in all clinical laboratories limits its widespread use. In the case of COVID-19, these tests can be used for the triage of symptomatic patients, for testing the contacts of confirmed cases, and also for the analysis and monitoring of the situation. Along with molecular tests involving reverse transcription PCR, various laboratory tests can identify the specific anti-viral antibodies or viral antigens. This review seeks to describe the targets and diagnostic methods available or currently in development for SARS-CoV-2 infection, including reverse transcription PCR (RT-PCR), serologic immunoassays (SIA) and the protein microarray method (PMM). Knowing the specific targets and the sensitivity of each assay used for COVID-19 diagnosis can lead to more efficient detection of infected patients and it can provide better management of the pandemic status.