SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans

COVID-19: an 'extraterrestrial' disease?

BACKGROUND

Since the beginning of the pandemic, COVID-19 has been regarded as an exceptional disease. Control measures have exclusively focused on 'the virus', while failing to account for other biological and social factors that determine severe forms of the disease.

AIM

We argue that although COVID-19 was initially considered a new challenge, justifying extraordinary response measures, this situation has changed - and so should our response.

MAIN ARGUMENTS

We now know that COVID-19 shares many features of common infectious respiratory diseases, and can now ascertain that SARS-CoV-2 has not suddenly presented new problems. Instead, it has exposed and exacerbated existing problems in health systems and the underlying health of the population. COVID-19 is evidently not an 'extraterrestrial' disease. It is a complex zoonotic disease, and it needs to be managed as such, following long-proven principles of medicine and public health.

CONCLUSION

A complex disease cannot be solved through a simple, magic-bullet cure or vaccine. The heterogeneity of population profiles susceptible to developing a severe form of COVID-19 suggests the need to adopt varying, targeted measures that are able to address risk profiles in an appropriate way. The critical role of comorbidities in disease severity calls for short-term, virus-targeted interventions to be complemented with medium-term policies aimed at reducing the burden of comorbidities, as well as mitigating the risk of transition from infection to disease. Strategies required include upstream prevention, early treatment, and consolidation of the health system.

Robust immune responses after one dose of BNT162b2 mRNA vaccine dose in SARS-CoV-2 experienced individuals

The use of COVID-19 vaccines will play the major role in helping to end the pandemic that has killed millions worldwide. COVID-19 vaccines have resulted in robust humoral responses and protective efficacy in human trials, but efficacy trials excluded individuals with a prior diagnosis of COVID-19. As a result, little is known about how immune responses induced by mRNA vaccines differ in individuals who recovered from COVID-19. Here, we evaluated longitudinal immune responses to two-dose BNT162b2 mRNA vaccination in 15 adults who recovered from COVID-19, compared to 21 adults who did not have prior COVID-19 diagnosis. Consistent with prior studies of mRNA vaccines, we observed robust cytotoxic CD8+ T cell responses in both cohorts following the second dose. Furthermore, SARS-CoV-2-naive individuals had progressive increases in humoral and antigen-specific antibody-secreting cell (ASC) responses following each dose of vaccine, whereas SARS-CoV-2-experienced individuals demonstrated strong humoral and antigen-specific ASC responses to the first dose but muted responses to the second dose of the vaccine at the time points studied. Together, these data highlight the relevance of immunological history for understanding vaccine immune responses and may have significant implications for personalizing mRNA vaccination regimens used to prevent COVID-19, including booster shots.

Large-scale study of antibody titer decay following BNT162b2 mRNA vaccine or SARS-CoV-2 infection

BACKGROUND

Immune protection following either vaccination or infection with SARS-CoV-2 decreases over time.

OBJECTIVE

To determine the kinetics of SARS-CoV-2 IgG antibodies following administration of two doses of BNT162b2 vaccine, or SARS-CoV-2 infection in unvaccinated individuals.

METHODS

Antibody titers were measured between January 31, 2021, and July 31, 2021 in two mutually exclusive groups: i) vaccinated individuals who received two doses of BNT162b2 vaccine and had no history of previous infection with COVID-19 and ii) SARS-CoV-2 convalescents who had not received the vaccine.

RESULTS

A total of 2,653 individuals fully vaccinated by two doses of vaccine during the study period and 4,361 convalescent patients were included. Higher SARS-CoV-2 IgG antibody titers were observed in vaccinated individuals (median 1581 AU/mL IQR [533.8-5644.6]) after the second vaccination, than in convalescent individuals (median 355.3 AU/mL IQR [141.2-998.7]; p<0.001). In vaccinated subjects, antibody titers decreased by up to 40% each subsequent month while in convalescents they decreased by less than 5% per month. Six months after BNT162b2 vaccination 16.1% subjects had antibody levels below the seropositivity threshold of <50 AU/mL, while only 10.8% of convalescent patients were below <50 AU/mL threshold after 9 months from SARS-CoV-2 infection.

CONCLUSIONS

This study demonstrates individuals who received the Pfizer-BioNTech mRNA vaccine have different kinetics of antibody levels compared to patients who had been infected with the SARS-CoV-2 virus, with higher initial levels but a much faster exponential decrease in the first group.

FUNDING

This research was internally funded by Leumit Health Services (LHS) and was supported in part by the Intramural Research Program, National Institutes of Health, National Cancer Institute, Center for Cancer Research.The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

IMPACT STATEMENT

Large scale study display the kinetics of SARS-CoV-2 IgG antibodies present in individuals vaccinated with two doses of mRNA vaccine vs. unvaccinated patients who had recovered from the disease: initial levels of antibody are much higher in vaccinated patients, but decrease faster.

Integrated longitudinal immunophenotypic, transcriptional and repertoire analyses delineate immune responses in COVID-19 patients

To understand how a protective immune response against SARS-CoV-2 develops over time, we integrated phenotypic, transcriptional and repertoire analyses on PBMCs from mild and severe COVID-19 patients during and after infection, and compared them to healthy donors (HD). A type I IFN-response signature marked all the immune populations from severe patients during the infection. Humoral immunity was dominated by IgG production primarily against the RBD and N proteins, with neutralizing antibody titers increasing post infection and with disease severity. Memory B cells, including an atypical FCRL5⁺ T-BET⁺ memory subset, increased during the infection, especially in patients with mild disease. A significant reduction of effector memory, CD8⁺ T cells frequency characterized patients with severe disease. Despite such impairment, we observed robust clonal expansion of CD8⁺ T lymphocytes, while CD4⁺ T cells were less expanded and skewed toward T_CM and T_H2-like phenotypes. MAIT cells were also expanded, but only in patients with mild disease. Terminally differentiated CD8⁺ GZMB⁺ effector cells were clonally expanded both during the infection and post-infection, while CD8⁺ GZMK⁺ lymphocytes were more expanded post-infection and represented bona fide memory precursor effector cells. TCR repertoire analysis revealed that only highly proliferating T cell clonotypes, which included SARS-CoV-2-specific cells, were maintained post-infection and shared between the CD8⁺ GZMB⁺ and GZMK⁺ subsets. Overall, this study describes the development of immunity against SARS-CoV-2 and identifies an effector CD8⁺ T cell population with memory precursor-like features.

Protection against SARS-CoV-2 Beta Variant in mRNA-1273 Boosted Nonhuman Primates

Neutralizing antibody responses gradually wane after vaccination with mRNA-1273 against several variants of concern (VOC), and additional boost vaccinations may be required to sustain immunity and protection. Here, we evaluated the immune responses in nonhuman primates that received 100 µg of mRNA-1273 vaccine at 0 and 4 weeks and were boosted at week 29 with mRNA-1273 (homologous) or mRNA-1273.β (heterologous), which encompasses the spike sequence of the B.1.351 (beta or β) variant. Reciprocal ID ₅₀ pseudovirus neutralizing antibody geometric mean titers (GMT) against live SARS-CoV-2 D614G and the β variant, were 4700 and 765, respectively, at week 6, the peak of primary response, and 644 and 553, respectively, at a 5-month post-vaccination memory time point. Two weeks following homologous or heterologous boost β-specific reciprocal ID ₅₀ GMT were 5000 and 3000, respectively. At week 38, animals were challenged in the upper and lower airway with the β variant. Two days post-challenge, viral replication was low to undetectable in both BAL and nasal swabs in most of the boosted animals. These data show that boosting with the homologous mRNA-1273 vaccine six months after primary immunization provides up to a 20-fold increase in neutralizing antibody responses across all VOC, which may be required to sustain high-level protection against severe disease, especially for at-risk populations.

ONE-SENTENCE SUMMARY

mRNA-1273 boosted nonhuman primates have increased immune responses and are protected against SARS-CoV-2 beta infection.

Walking down the memory lane with SARS-CoV-2 B cells

The B-cell response to COVID-19 vaccines in convalescent individuals.

Factors Affecting the Antibody Immunogenicity of Vaccines against SARS-CoV-2: A Focused Review

Vaccines are a crucial part of the global anti-pandemic effort against COVID-19. The effects of vaccines, as well as their common influencing factors, are the most important issues that we should focus on at this time. To this end, we review statistics on immunogenicity after vaccination, using neutralizing antibodies as the main reference index. Age, infection history, and virus variants are compared, and vaccination program recommendations are made accordingly. Suggestions are made to address concerns raised by the vaccines' shortened development cycle, as well as the emergence of immunity escape of viral variants. Finally, a brief description and future prospects are provided based on the principle of the ADE effect and previous experience with similar viruses.

Longitudinal observation of antibody responses for 14 months after SARS-CoV-2 infection

Better understanding of antibody responses against SARS-CoV-2 after natural infection might provide valuable insights into the future implementation of vaccination policies. Longitudinal analysis of IgG antibody titers was carried out in 32 recovered COVID-19 patients based in the Umbria region of Italy for 14 months after Mild and Moderately-Severe infection.Two FDA-approved immunoassays against SARS-CoV-2 Nucleocapsid protein (NCP) and anti-spike-receptor binding domain (S-RBD) were used for sequential serological tests at different time points. The demographics,clinical history and symptom profile associated with the magnitude and longevity of antibody responses were also analyzed. Anti-S-RBD IgG persisted in 96.8% (31 of 32) subjects at 14 months. Patients reporting loss of smell and taste during the clinical course of the disease developed significantly higher antibody titers. Anti-NCP IgG seronegative patients(n=7) at 10 months, tested positive for anti-S-RBD IgG at 12,13 and 14 months emphasizing on a higher false-negative rate for NCP protein-based antibody assays. This study also highlights the importance of adopting specific immunoassays for routine estimation of antibody titers and the decreased rate of re-infections in recovered patients.

One Year after Mild COVID-19: The Majority of Patients Maintain Specific Immunity, But One in Four Still Suffer from Long-Term Symptoms

After COVID-19, some patients develop long-term symptoms. Whether such symptoms correlate with immune responses, and how long immunity persists, is not yet clear. This study focused on mild COVID-19 and investigated correlations of immunity with persistent symptoms and immune longevity. Persistent complications, including headache, concentration difficulties and loss of smell/taste, were reported by 51 of 83 (61%) participants and decreased over time to 28% one year after COVID-19. Specific IgA and IgG antibodies were detectable in 78% and 66% of participants, respectively, at a 12-month follow-up. Median antibody levels decreased by approximately 50% within the first 6 months but remained stable up to 12 months. Neutralizing antibodies could be found in 50% of participants; specific INFgamma-producing T-cells were present in two thirds one year after COVID-19. Activation-induced marker assays identified specific T-helper cells and central memory T-cells in 80% of participants at a 12-month follow-up. In correlative analyses, older age and a longer duration of the acute phase of COVID-19 were associated with higher humoral and T-cell responses. A weak correlation between long-term loss of taste/smell and low IgA levels was found at early time points. These data indicate a long-lasting immunological memory against SARS-CoV-2 after mild COVID-19.

Immune Assessment of BNT162b2 m-RNA-Spike Based Vaccine Response in Adults

Vaccine efficacy is based on clinical data. Currently, the assessment of immune response after SARS-CoV-2 vaccination is scarce. A total of 52 healthcare workers were immunized with the same lot of BNT162b2 vaccine. The immunological response against the vaccine was tested using a T-specific assay based on the expression of CD25 and CD134 after stimulation with anti-N, -S, and -M specific peptides of SARS-CoV-2. Moreover, IgG anti-S2 and -RBD antibodies were detected using ELISA. Furthermore, the cell subsets involved in the response to the vaccine were measured in peripheral blood by flow cytometry. Humoral-specific responses against the vaccine were detected in 94% and 100% after the first and second doses, respectively. Therefore, anti-S T-specific responses were observed in 57% and 90% of the subjects after the first and second doses of the vaccine, respectively. Thirty days after the second dose, significant increases in T helper 1 memory cells (p < 0.001), peripheral memory T follicular helper (pT_FH) cells (p < 0.032), and switched memory (p = 0.005) were observed. This study describes the specific humoral and cellular immune responses after vaccination with the new mRNA-based BNT162b2 vaccine. A mobilization of T_FH into the circulation occurs, reflecting a specific activation of the immune system.

Affinity Tag Coating Enables Reliable Detection of Antigen-Specific B Cells in Immunospot Assays

Assessment of humoral immunity to SARS-CoV-2 and other infectious agents is typically restricted to detecting antigen-specific antibodies in the serum. Rarely does immune monitoring entail assessment of the memory B-cell compartment itself, although it is these cells that engage in secondary antibody responses capable of mediating immune protection when pre-existing antibodies fail to prevent re-infection. There are few techniques that are capable of detecting rare antigen-specific B cells while also providing information regarding their relative abundance, class/subclass usage and functional affinity. In theory, the ELISPOT/FluoroSpot (collectively ImmunoSpot) assay platform is ideally suited for antigen-specific B-cell assessments since it provides this information at single-cell resolution for individual antibody-secreting cells (ASC). Here, we tested the hypothesis that antigen-coating efficiency could be universally improved across a diverse set of viral antigens if the standard direct (non-specific, low affinity) antigen absorption to the membrane was substituted by high-affinity capture. Specifically, we report an enhancement in assay sensitivity and a reduction in required protein concentrations through the capture of recombinant proteins via their encoded hexahistidine (6XHis) affinity tag. Affinity tag antigen coating enabled detection of SARS-CoV-2 Spike receptor binding domain (RBD)-reactive ASC, and also significantly improved assay performance using additional control antigens. Collectively, establishment of a universal antigen-coating approach streamlines characterization of the memory B-cell compartment after SARS-CoV-2 infection or COVID-19 vaccinations, and facilitates high-throughput immune-monitoring efforts of large donor cohorts in general.

Longitudinal analysis shows durable and broad immune memory after SARS-CoV-2 infection with persisting antibody responses and memory B and T cells

Ending the COVID-19 pandemic will require long-lived immunity to SARS-CoV-2. Here, we evaluate 254 COVID-19 patients longitudinally up to 8 months and find durable broad-based immune responses. SARS-CoV-2 spike binding and neutralizing antibodies exhibit a bi-phasic decay with an extended half-life of >200 days suggesting the generation of longer-lived plasma cells. SARS-CoV-2 infection also boosts antibody titers to SARS-CoV-1 and common betacoronaviruses. In addition, spike-specific IgG+ memory B cells persist, which bodes well for a rapid antibody response upon virus re-exposure or vaccination. Virus-specific CD4+ and CD8+ T cells are polyfunctional and maintained with an estimated half-life of 200 days. Interestingly, CD4+ T cell responses equally target several SARS-CoV-2 proteins, whereas the CD8+ T cell responses preferentially target the nucleoprotein, highlighting the potential importance of including the nucleoprotein in future vaccines. Taken together, these results suggest that broad and effective immunity may persist long-term in recovered COVID-19 patients.

The success of SARS-CoV-2 vaccines and challenges ahead

The rapid and remarkably successful development, manufacture, and deployment of several effective severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines is now tempered by three key challenges. First, reducing virus transmission will require prevention of asymptomatic and mild infections in addition to severe symptomatic infections. Second, the emergence of variants of concern with mutations in the S protein's receptor binding domain increases the likelihood that vaccines will have to be updated because some of these mutations render variants less optimally targeted by current vaccines. This will require coordinated global SARS-CoV-2 surveillance to link genotypes to phenotypes, potentially using the WHO's global influenza surveillance program as a guide. Third, concerns about the longevity of vaccine-induced immunity highlight the potential need for re-vaccination, depending on the extent to which the virus has been controlled and whether re-vaccination can target those at greatest risk of severe illness. Fortunately, as I discuss in this review, these challenges can be addressed.

Beyond neutralization for BNT162b2 mRNA vaccination

Mounting a robust immune response against SARS-CoV-2 requires neutralization as well as effector T cell functions. In this issue of Cell Host Microbe, Tauzin et al. characterize the humoral and T cell responses after a single dose of BNT162b2 mRNA vaccine in individuals with or without previous exposure to SARS-CoV-2.

Surviving older patients show preserved cellular and humoral immunological memory several months after SARS-CoV-2 infection

Understanding how older people respond to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is critical if we are to confront the coronavirus disease 2019 (COVID-19) pandemic and establish effective vaccination strategies. Immunosenescence reduces the ability to respond to neoantigens and may compromise the life of infected individuals. Here, we analyzed the immunological memory to SARS-CoV-2 in 102 recovered patients aged over 60 years several months after the infection had been resolved. Specific memory T lymphocytes against the virus were measured by interferon-γ (IFN-γ) and granzyme B release by ELISpot; memory B-lymphocyte responses were quantified by detection of anti-S IgG1 producer cells by ELISpot and anti-S and anti-N antibodies were determined by enzyme-linked immunosorbent assay (ELISA). Memory T lymphocytes were found in peripheral blood of most of the studied donors, more than 7 months after the infection in some of them. Fewer patients maintained memory B lymphocytes, but antibodies, mainly anti-S, were highly durable and positively correlated with T responses. More robust humoral responses were found in patients who had more severe symptoms and had been admitted to hospital. We concluded that specific immunity against SARS-CoV-2 is effectively preserved regardless of age, despite the great heterogeneity of their immune responses, and that memory T lymphocytes and anti-S IgG might be more durable than memory B cells and anti-N IgG.

Naive human B cells engage the receptor binding domain of SARS-CoV-2, variants of concern, and related sarbecoviruses

Exposure to a pathogen elicits an adaptive immune response aimed to control and eradicate. Interrogating the abundance and specificity of the naive B cell repertoire contributes to understanding how to potentially elicit protective responses. Here, we isolated naive B cells from 8 seronegative human donors targeting the SARS-CoV-2 receptor-binding domain (RBD). Single B cell analysis showed diverse gene usage with no restricted complementarity determining region lengths. We show that recombinant antibodies engage SARS-CoV-2 RBD, circulating variants, and pre-emergent coronaviruses. Representative antibodies signal in a B cell activation assay and can be affinity matured through directed evolution. Structural analysis of a naive antibody in complex with spike shows a conserved mode of recognition shared with infection-induced antibodies. Lastly, both naive and affinity-matured antibodies can neutralize SARS-CoV-2. Understanding the naive repertoire may inform potential responses recognizing variants or emerging coronaviruses enabling the development of pan-coronavirus vaccines aimed at engaging germline responses.

Isolation of antibody germline precursors targeting the receptor binding domain of coronaviruses.

Twelve-month specific IgG response to SARS-CoV-2 receptor-binding domain among COVID-19 convalescent plasma donors in Wuhan

To investigate the duration of humoral immune response in convalescent coronavirus disease 2019 (COVID-19) patients, we conduct a 12-month longitudinal study through collecting a total of 1,782 plasma samples from 869 convalescent plasma donors in Wuhan, China and test specific antibody responses. The results show that positive rate of IgG antibody against receptor-binding domain of spike protein (RBD-IgG) to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the COVID-19 convalescent plasma donors exceeded 70% for 12 months post diagnosis. The level of RBD-IgG decreases with time, with the titer stabilizing at 64.3% of the initial level by the 9th month. Moreover, male plasma donors produce more RBD-IgG than female, and age of the patients positively correlates with the RBD-IgG titer. A strong positive correlation between RBD-IgG and neutralizing antibody titers is also identified. These results facilitate our understanding of SARS-CoV-2-induced immune memory to promote vaccine and therapy development.

Cell fate dynamics and genomic programming of plasma cell precursors

This review is focused on the cellular dynamics and genomic programming of plasma cell (PC) precursors that arise during germinal center (GC) B cell responses in secondary lymphoid organs (SLOs) and give rise to PCs in the bone marrow. Considerable progress has been made in the phenotypic characterization of circulating and bone marrow PC precursors as well as their differentiated short-lived (SLPC) and long-lived (LLPC) counterparts, in the context of model antigen and vaccine responses. Importantly, it has been possible to infer the temporal dynamics of generation of PC precursors during a GC response. However, the nature of the PC precursors at their site of generation in SLOs, and their signaling and genomic states, remain to be elucidated. Our synthesis draws upon experimental studies conducted in murine models as well as in humans, the latter complemented with cell culture manipulations of PCs and their precursors. By integration of the studies in murine and human systems, which are being accelerated by new genomic methodologies, we highlight insights and hypotheses concerning the generation of PCs. This framework can be extended and explored from both fundamental and translational standpoints.

SARS-CoV-2 Portrayed against HIV: Contrary Viral Strategies in Similar Disguise

SARS-CoV-2 and HIV are zoonotic viruses that rapidly reached pandemic scale, causing global losses and fear. The COVID-19 and AIDS pandemics ignited massive efforts worldwide to develop antiviral strategies and characterize viral architectures, biological and immunological properties, and clinical outcomes. Although both viruses have a comparable appearance as enveloped viruses with positive-stranded RNA and envelope spikes mediating cellular entry, the entry process, downstream biological and immunological pathways, clinical outcomes, and disease courses are strikingly different. This review provides a systemic comparison of both viruses' structural and functional characteristics, delineating their distinct strategies for efficient spread.

Longitudinal analysis shows durable and broad immune memory after SARS-CoV-2 infection with persisting antibody responses and memory B and T cells

Ending the COVID-19 pandemic will require long-lived immunity to SARS-CoV-2. Here, we evaluate 254 COVID-19 patients longitudinally up to eight months and find durable broad-based immune responses. SARS-CoV-2 spike binding and neutralizing antibodies exhibit a bi-phasic decay with an extended half-life of >200 days suggesting the generation of longer-lived plasma cells. SARS-CoV-2 infection also boosts antibody titers to SARS-CoV-1 and common betacoronaviruses. In addition, spike-specific IgG+ memory B cells persist, which bodes well for a rapid antibody response upon virus re-exposure or vaccination. Virus-specific CD4+ and CD8+ T cells are polyfunctional and maintained with an estimated half-life of 200 days. Interestingly, CD4+ T cell responses equally target several SARS-CoV-2 proteins, whereas the CD8+ T cell responses preferentially target the nucleoprotein, highlighting the potential importance of including the nucleoprotein in future vaccines. Taken together, these results suggest that broad and effective immunity may persist long-term in recovered COVID-19 patients.

Antibody longevity and cross-neutralizing activity following SARS-CoV-2 wave 1 and B.1.1.7 infections

As SARS-CoV-2 variants continue to emerge globally, a major challenge for COVID-19 vaccination is the generation of a durable antibody response with cross-neutralizing activity against both current and newly emerging viral variants. Cross-neutralizing activity against major variants of concern (B.1.1.7, P.1 and B.1.351) has been observed following vaccination, albeit at a reduced potency, but whether vaccines based on the Spike glycoprotein of these viral variants will produce a superior cross-neutralizing antibody response has not been fully investigated. Here, we used sera from individuals infected in wave 1 in the UK to study the long-term cross-neutralization up to 10 months post onset of symptoms (POS), as well as sera from individuals infected with the B.1.1.7 variant to compare cross-neutralizing activity profiles. We show that neutralizing antibodies with cross-neutralizing activity can be detected from wave 1 up to 10 months POS. Although neutralization of B.1.1.7 and B.1.351 is lower, the difference in neutralization potency decreases at later timepoints suggesting continued antibody maturation and improved tolerance to Spike mutations. Interestingly, we found that B.1.1.7 infection also generates a cross-neutralizing antibody response, which, although still less potent against B.1.351, can neutralize parental wave 1 virus to a similar degree as B.1.1.7. These findings have implications for the optimization of vaccines that protect against newly emerging viral variants.

Persistence of Antibody and Cellular Immune Responses in COVID-19 patients over Nine Months after Infection

Background

The duration of humoral and T and cell response after the infection of SARS-CoV-2 remains unclear.

Methods

We performed a cross-sectional study to assess the virus-specific antibody and memory T and B cell responses in COVID-19 patients up to 343 days after infection. Neutralizing antibodies and antibodies against the receptor-binding domain, spike, and nucleoprotein of SARS-CoV-2 were measured. Virus-specific memory T and B cell responses were analyzed.

Results

We enrolled 59 COVID-19 patients, including 38 moderate, 16 mild, and five asymptomatic patients; 31 (52.5%) were men, and 28 (47.5%) were women. The median age was 41 (interquartile range [IQR]: 30–55). The median day from symptom onset to enrollment was 317 days (range 257 to 343 days). We found that approximately 90% of patients still have detectable IgG antibodies against spike and nucleocapsid proteins and neutralizing antibodies against pseudovirus, whereas ~60% of patients had detectable IgG antibodies against receptor binding domain and surrogate virus-neutralizing antibodies. SARS-CoV-2-specific IgG ⁺ memory B cell and IFN-γ secreting T cell responses were detectable in over 70% of patients.

Conclusions

SARS-CoV-2-specific immune memory response persists in most patients nearly one year after infection, which provides a promising sign for prevention from reinfection and vaccination strategy.

SARS-CoV-2 immunity and an overview of the COVID-19 vaccines

The remarkable development of a large number of vaccines against COVID-19 in a very short period of time represents one of the greatest successes of medicine and science in history, and mass vaccination at the global level will be crucial for prevention and mitigation of COVID-19. However, there are still numerous open questions about the vaccines, and the protection they provide, and answers to those questions will not only help to control this pandemic, but they will also prepare us to react better in case of future outbreaks. This review will present the latest findings on the immune response to SARS-CoV-2 and give an update on COVID-19 immunity. It will also provide an overview of the most important vaccines against COVID-19, especially those available in Serbia, with an emphasis on their immunogenicity, efficacy and safety, as well as the platforms used for their development. In addition, a special attention will be given to open issues related to immunization against COVID-19, such as the duration of post-vaccination immunity, the degree of protection against new virus variants and the need for booster doses and mixing and matching of different COVID-19 vaccines.