Immune responses after twofold SARS-CoV-2 immunisation in elderly residents and Health Care Workers in nursing homes and homes with assisted living support - Proposal for a correlate of protection (preprint)

In the present study, we were interested in the decline over time of anti SARS-CoV-2 antibodies and SARS-CoV-2 specific T-cell responses after two doses of mRNA vaccines in total and by age group and comorbidity. The second goal was to suggest an immunological correlate for protection on an individual basis and to describe the probability of protection over time after second vaccination. We analysed blood samples from 228 residents (median age 83.8 years) and from 273 Health Care Workers (HCW; median age 49.7 years) of five nursing homes and one home for the elderly with assisted living support. Participants had received two vaccinations. The blood samples were analysed for SARS-CoV-2 specific antibody and T-cell responses. We compared outcomes in the HCW and residents in the respective institutions. No breakthrough infections occurred during the study period. The initial immune responses in the younger participants were about 30 % higher than in the older ones. Over time, all parameters dropped continuously in all groups within the maximum observation period of 232 days. Comorbidities such as coronary heart disease or diabetes mellitus reduced the initial immune responses, regardless of age. In contrast to an almost linear decline in antibody levels, we observed that the interferon-gamma response remained at a constant level between about day 120 and 180, only to decline further thereafter. Based on our data, we propose on an individual level a correlate of protection: Persons who have a neutralizing capacity of 75 % (which would correspond to approx. 200 BAU/ml) and an interferon-gamma response above 200 mIU/ml should be considered to be protected resp. sufficiently immunized.

Long-term course of humoral and cellular immune responses in outpatients after SARS-CoV-2 infection (preprint)

Characterisation of the naturally acquired B and T cell immune responses to SARS-CoV-2 is important for the development of public health and vaccination strategies to manage the burden of COVID-19 disease. We conducted a prospective, longitudinal analysis in COVID-19 recovered patients at various time points over a 10-month period in order to determine how circulating antibody levels and interferon-gamma (IFN-{gamma}) release by peripheral blood cells change over time following natural infection. From March 2020 till January 2021, we enrolled 412 adults mostly with mild or moderate disease course. At each study visit, subjects donated peripheral blood for testing of anti-SARS-CoV-2 IgG antibodies and IFN-{gamma} release after SARS-CoV-2 S-protein stimulation. Anti-SARS-CoV-2 IgG antibodies were identified in 316/412 (76.7%) of the patients and 215/412 (52.2%) had positive neutralizing antibody levels. Likewise, in 274/412 (66.5 %) positive IFN-{gamma} release and IgG antibodies were detected. With respect to time after infection, both IgG antibody levels and IFN-{gamma} concentrations decreased by about half within three hundred days. Statistically, IgG and IFN-{gamma} production were closely associated, but on an individual basis we observed patients with high antibody titres but low IFN-{gamma} levels and vice versa. Our data suggest that immunological reaction is acquired in most individuals after infection with SARS-CoV-2 and is sustained in the majority of patients for at least 10 months after infection. Since no robust marker for protection against COVID-19 exists so far, we recommend utilizing both, IgG and IFN-{gamma} release for an individual assessment of immunity status.

Antibody profiling of COVID-19 patients in an urban low-incidence region in Northern Germany (preprint)

This explorative monocentric study shows IgA and IgG antibody profiles from 110 patients with self-reported mild to moderate, or no COVID-19 related symptoms after laboratory-confirmed infection with SARS-CoV-2. The study region is in an urban and well-defined environment in a low-incidence region in Northern Germany. We found that approx. 70 % of the patients developed sustainable antibodies 3 weeks or later after the infection. In about 30 % of the patients with mild to moderate symptoms, no significant antibodies could be detected in two consecutive analyses. Conversely, out of ten patients without symptoms, four were repeatedly positive. Expectedly, six had no specific antibodies. The data indicate that antibody-positivity is a useful indicator of a previous SARS-CoV-2 infection. Negative antibodies do not rule out SARS-CoV-2 infection. Future studies need to determine the functionality of the antibodies in terms of personal protection and ability to transmit the virus.