Comparable antigen-specific T cell responses in vaccinees with diverse humoral immune responses after primary and booster BBIBP-CorV vaccination

Durability and cross-reactive immune memory to SARS-CoV-2 in individuals 2 years after recovery from COVID-19: a longitudinal cohort study

BACKGROUND

SARS-CoV-2-specific adaptive immunity more than 1 year after initial infection has not been well characterised. The aim of this study was to investigate the durability and cross-reactivity of immunological memory acquired from natural infection against SARS-CoV-2 in individuals recovered from COVID-19 2 years after infection.

METHODS

In this longitudinal cohort study, we recruited patients who had recovered from laboratory-confirmed COVID-19 and were discharged from Jinyintan Hospital (Wuhan, China) between Jan 7 and May 29, 2020. We carried out three successive follow-ups between June 16 and Sept 3, 2020 (6 months), Dec 16, 2020, and Feb 7, 2021 (1 year), and Nov 16, 2021, and Jan 10, 2022 (2 years), in which blood samples were taken. We included participants who did not have re-infection or receive a SARS-CoV-2 vaccination (infected-unvaccinated), and participants who received one to three doses of inactivated vaccine 1-2 years after infection (infected-vaccinated). We evaluated the presence of IgG antibodies, neutralising antibodies, and memory B-cell and memory T-cell responses against the prototype strain and delta and omicron variants.

FINDINGS

In infected-unvaccinated participants, neutralising antibody titres continually declined from 6-month to 2-year follow-up visits, with a half-life of about 141·2 days. Neutralising antibody responses to omicron sublineages (BA.1, BA.1.1, BA.2, BA.4/5, BF.7, BQ.1, and XBB) were poor. Memory B-cell responses to the prototype strain were retained at 2 years and presented cross-reactivity to the delta and omicron BA.1 variants. The magnitude of interferon γ and T-cell responses to SARS-CoV-2 were not significantly different between 1 year and 2 years after infection. Multifunctional T-cell responses against SARS-CoV-2 spike protein and nucleoprotein were detected in most participants. Recognition of the BA.1 variant by memory T cells was not affected in most individuals. The antibody titres and the frequencies of memory B cells, but not memory T cells, increased in infected-vaccinated participants after they received the inactivated vaccine.

INTERPRETATION

This study improves the understanding of the duration of SARS-CoV-2-specific immunity without boosting, which has implications for the design of vaccination regimens and programmes. Our data suggest that memory T-cell responses primed by initial viral infection remain highly cross-reactive after 2 years. With the increasing emergence of variants, effective vaccines should be introduced to boost neutralising antibody and overall T-cell responses to newly emerged SARS-CoV-2 variants.

FUNDING

Chinese Academy of Medical Sciences, National Natural Science Foundation of China, Fundamental Research Funds for the Central Universities for Peking Union Medical College, Beijing Natural Science Foundation, UK Medical Research Council.

Sequential reinfection with Omicron variants elicits broader neutralizing antibody profiles in booster vaccinees and reduces the duration of viral shedding

The constant emergence of breakthrough infections with Omicron variants poses an escalating challenge to the current vaccination strategy. In this study, we investigated the distinct neutralization activities and clinical characteristics of the booster vaccinees with Omicron reinfection compared with single breakthrough infection and homologous booster vaccination. Our results demonstrate that neutralizing antibody GMTs for WT and other four subvariants (BA.2.2, BA.5.2, BF.7, and XBB.1) differ greatly between breakthrough infection and homologous booster cohorts. Sequential reinfection with Omicron variants elicits broader and high-titer variant-specific neutralizing antibody profiles against Omicron variants. It could also dampen the hyperactivation of WT-specific neutralization induced by previous WT-based vaccination. Moreover, the clinical characteristics from reinfection demonstrated that repeated stimulation by Omicron variants could reduce the duration of viral shedding. By considering reinfection with the Omicron variant as a representative model of repeated immunogen exposures, our results thus illustrate the potential superiority of repeated Omicron stimuli and provide additional evidence supporting the Omicron immunogen as a more effective vaccine candidate to mitigate the transmission of emerging variants.