Hybrid immunity from SARS-CoV-2 infection and vaccination in Canadian adults: cohort study (preprint)

BackgroundFew national-level studies have evaluated the impact of "hybrid" immunity (vaccination coupled with recovery from infection) from the Omicron variants of SARS-CoV-2. MethodsFrom May 2020 to December 2022, we conducted serial assessments (each of [~]4000-9000 adults) examining SARS-CoV-2 antibodies within a mostly representative Canadian cohort drawn from a national online polling platform. Adults, most of whom were vaccinated, reported viral test-confirmed infections and mailed self-collected dried blood spots to a central lab. Samples underwent highly sensitive and specific antibody assays to spike and nucleocapsid protein antigens, the latter triggered only by infection. We estimated cumulative SARS-CoV-2 incidence prior to the Omicron period and during the BA.1/1.1 and BA.2/5 waves. We assessed changes in antibody levels and in age-specific active immunity levels. ResultsSpike levels were higher in infected than in uninfected adults, regardless of vaccination doses. Among adults vaccinated at least thrice and infected more than six months earlier, spike levels fell notably and continuously for the nine months post-vaccination. By contrast, among adults infected within six months, spike levels declined gradually. Declines were similar by sex, age group, and ethnicity. Recent vaccination attenuated declines in spike levels from older infections. In a convenience sample, spike antibody and cellular responses were correlated. Near the end of 2022, about 35% of adults above age 60 had their last vaccine dose more than six months ago, and about 25% remained uninfected. The cumulative incidence of SARS-CoV-2 infection rose from 13% (95% CI 11-14%) before omicron to 78% (76-80%) by December 2022, equating to 25 million infected adults cumulatively. However, the COVID-19 weekly death rate during the BA.2/5 waves was less than half of that during the BA.1/1.1 wave, implying a protective role for hybrid immunity. ConclusionsStrategies to maintain population-level hybrid immunity require up-to-date vaccination coverage, including among those recovering from infection. Population-based, self-collected dried blood spots are a practicable biological surveillance platform. FundingFunding was provided by the COVID-19 Immunity Task Force, Canadian Institutes of Health Research, Pfizer Global Medical Grants, and St. Michaels Hospital Foundation. PJ and ACG are funded by the Canada Research Chairs Program.

Omicron Breakthrough Infection Elicits Superior Humoral and Mucosal Immune Responses to SARS-CoV-2 Variants than an Intramuscular Booster Dose (preprint)

Our understanding of the quality of cellular and humoral immunity conferred by COVID-19 vaccination alone versus vaccination plus SARS-CoV-2 breakthrough (BT) infection remains incomplete. While the current (2023) SARS-CoV-2 immune landscape of Canadians is complex, in late 2021 most Canadians had either just received a third dose of COVID-19 vaccine, or had received their two dose primary series and then experienced an Omicron BT. Herein we took advantage of this coincident timing to contrast cellular and humoral immunity conferred by three doses of vaccine versus two doses plus BT. Our results show that mild BT infection induces cell-mediated immune responses to variants comparable to an intramuscular vaccine booster dose. In contrast, BT subjects had higher salivary IgG and IgA levels against the Omicron Spike and enhanced reactivity to the ancestral Spike for the IgA isotype, which also reacted with SARS-CoV-1. Serum neutralizing antibody levels against the ancestral strain and the variants were also higher after BT infection. Our results support the need for mucosal vaccines to emulate the enhanced mucosal and humoral immunity induced by Omicron without exposing individuals to the risks associated with SARS-CoV-2 infection.

Immunogenicity of COVID-19 vaccines and their effect on the HIV reservoir in older people with HIV (preprint)

Older individuals and people with HIV (PWH) were prioritized for COVID-19 vaccination, yet comprehensive studies of the immunogenicity of these vaccines and their effects on HIV reservoirs are not available. We followed 68 PWH aged 55 and older and 23 age-matched HIV-negative individuals for 48 weeks from the first vaccine dose, after the total of three doses. All PWH were on antiretroviral therapy (cART) and had different immune status, including immune responders (IR), immune non-responders (INR), and PWH with low-level viremia (LLV). We measured total and neutralizing Ab responses to SARS-CoV-2 spike and RBD in sera, total anti-spike Abs in saliva, frequency of anti-RBD/NTD B cells, changes in frequency of anti-spike, HIV gag/nef-specific T cells, and HIV reservoirs in peripheral CD4+ T cells. The resulting datasets were used to create a mathematical model for within-host immunization. Various regimens of BNT162b2, mRNA-1273, and ChAdOx1 vaccines elicited equally strong anti-spike IgG responses in PWH and HIV-negative participants in serum and saliva at all timepoints. These responses had similar kinetics in both cohorts and peaked at 4 weeks post-booster (third dose), while half-lives of plasma IgG also dramatically increased post-booster in both groups. Salivary spike IgA responses were low, especially in INRs. PWH had diminished live virus neutralizing titers after two vaccine doses which were 'rescued' after a booster. Anti-spike T cell immunity was enhanced in IRs even in comparison to HIV-negative participants, suggesting Th1 imprinting from HIV, while in INRs it was the lowest. Increased frequency of viral 'blips' in PWH were seen post-vaccination, but vaccines did not affect the size of the intact HIV reservoir in CD4+ T cells in most PWH, except in LLVs. Thus, older PWH require three doses of COVID-19 vaccine to maximize neutralizing responses against SARS-CoV-2, although vaccines may increase HIV reservoirs in PWH with persistent viremia.

Omicron variant BA.1, BA.5, BQ.1.1, and XBB.1.5 Neutralizing Antibodies Following BNT162b2 BA.4/5 versus mRNA-1273 BA.1 Bivalent Vaccination (preprint)

Neutralization of Omicron subvariants by different bivalent vaccines have not been well evaluated. This study characterized neutralization against Omicron subvariants in 98 individuals receiving dialysis or with a kidney transplant receiving the BNT162b2 (BA.4/BA.5) or mRNA-1273 (BA.1) bivalent COVID-19 vaccine. Neutralization against Omicron BA.1, BA.5, BQ.1.1, and XBB.1.5 increased by 8-fold one month following bivalent vaccination. In comparison to wild-type (D614G), neutralizing antibodies against Omicron-specific variants were 7.3-fold lower against BA.1, 8.3-fold lower against BA.5, 45.8-fold lower against BQ.1.1, and 48.2-fold lower against XBB.1.5. Viral neutralization was not significantly different by bivalent vaccine type for wild-type (D614G) (P=0.48), BA.1 (P=0.21), BA.5 (P=0.07), BQ.1.1 (P=0.10), nor XBB.1.5 (P=0.10). Hybrid immunity conferred higher neutralizing antibodies against all Omicron subvariants. Given that both BNT162b2 (BA.4/BA.5) and mRNA-1273 (BA.1) induced similar neutralization against all Omicron subvariants, this suggests that bivalent vaccines confer protection even when they are antigenically divergent from the circulating variant.

Third and fourth vaccine doses broaden and prolong immunity to SARS-CoV-2 in immunocompromised adult patients (preprint)

Background. Previous studies have reported impaired humoral responses after SARS-CoV-2 mRNA vaccination in immunocompromised patients with immune-mediated inflammatory diseases (IMID), particularly those treated with anti-tumor necrosis factor (TNF) biologics. We previously reported that IMID patients exhibited greater waning of antibody and T cell responses compared to healthy controls after dose 2. Fewer data are available on the effects of third and fourth doses. Methods. This observational cohort study collected plasma and peripheral blood mononuclear cells from healthy controls and untreated or treated IMID patients, pre-vaccination and after one to four doses of SARS-CoV-2 mRNA vaccine (BNT162b2 or mRNA-1273). SARS-CoV-2- specific antibody levels, neutralization, and T cell cytokine responses were measured against Wildtype (WT) and BA.1 and BA.5 variants of concern (VOCs). Results. Third vaccine doses substantially restored and prolonged antibody and T cell responses in IMID patients and broadened responses against VOCs. Fourth dose effects were subtle but also prolonged antibody responses. However, IMID patients treated with anti-TNF, especially inflammatory bowel disease (IBD) patients, exhibited lower antibody responses even after the fourth dose. Although T cell IFN{gamma} responses were maximal after one dose, IL-2 and IL-4 production increased with successive doses, and early production of these cytokines was predictive of neutralization responses at 3-4 months post-vaccination. Conclusion. Our study demonstrates that third and fourth doses of the SARS-CoV-2 vaccine sustain and broaden immune responses to SARS-CoV-2, supporting the recommendation for three- and four-dose vaccination regimens in IMID patients. Funding. COVID-19 Immunity Task Force and Speck family donation

Protection from Omicron infection in residents of nursing and retirement homes in Ontario, Canada (preprint)

Objectives: To identify factors that contribute to protection from infection with the Omicron variant of SARS-CoV-2 in older adults in nursing and retirement homes. Design: Longitudinal cohort study with retrospective analysis of infection risk. Setting and Participants: 997 residents of nursing and retirement homes from Ontario, Canada, in the COVID-in-LTC study. Methods: Residents with three mRNA dose vaccinations were included in the study. SARS-CoV-2 infection was determined by positive nasopharyngeal PCR test and/or circulating anti-nucleocapsid IgG antibodies. Cumulative probability of Omicron infection after recent COVID-19 was assessed by log-rank test of Kaplan-Meier curves. Cox regression was used to assess risk of Omicron infection by age, sex, mRNA vaccine combination, whether individuals received a fourth dose, as well as recent COVID-19. Results: 171 residents (17.2%) had a presumed Omicron variant SARS-CoV-2 infection between December 15, 2021 (local start of the first Omicron wave) and May 3, 2022. Risk of Omicron infection was not different by age [hazard ratio (95% confidence interval): 1.01 (0.99-1.02)], or in women compared to men [0.97 (0.70-1.34)], but infection risk decreased 47% with three vaccine doses of mRNA-1273 (Moderna) compared to BNT162b2 (Pfizer) [0.53 (0.31-0.90)], 81% with any fourth mRNA vaccine dose [0.19 (0.12-0.30)], and 48% with SARS-CoV-2 infection in the 3 months prior to beginning of the Omicron wave [0.52, (0.27-0.99)]. Conclusions and Implications: Vaccine type (i.e., mRNA-1273/Spikevax vs BNT162b2/Cominarty), any fourth vaccine dose, and hybrid immunity from recent COVID-19, were protective against infection with the Omicron variant. These data emphasize the importance of vaccine type, and number of vaccine doses, in maintenance of protective immunity and reduction of risk of Omicron variant breakthrough infection. These findings promote continued public health efforts to support vaccination programs and monitor vaccine immunogenicity in older adults.

Phase I study of a SARS-CoV-2 mRNA vaccine PTX-COVID19-B (preprint)

PTX-COVID19-B mRNA vaccine encodes for SARS-CoV-2 Spike protein G614 variant and lacks the proline-proline (986-987 position) mutation present in other COVID-19 vaccines. This Phase 1 observer-blinded, randomized, placebo-controlled, ascending dose study evaluated the safety, tolerability, and immunogenicity of two doses of PTX-COVID19-B vaccine in healthy seronegative adults. Participants received two intramuscular doses, 4 weeks apart, of 16-g, 40-g, or 100-g PTX-COVID19-B. Adverse events were generally mild to moderate, self-resolving, and transient. The most common solicited local and systemic adverse event was pain at the injection site and headache, respectively. After the first immunization, all participants seroconverted, producing high titers of anti-receptor-binding-domain, anti-Spike, and neutralizing antibodies, including neutralizing antibodies against the ancestral viral strain and the Alpha, Beta, and Delta variants of concern, in a dose-dependent way, further increasing over 10-20 times after the second dose. All tested doses of PTX-COVID19-B were safe, well-tolerated, and provided a strong immunogenicity response. The 40-g dose showed fewer adverse reactions than the 100-g dose, supporting further investigation of the 40-g dose. Clinical Trial Registration: ClinicalTrials.gov identifier: NCT04765436 (https://clinicaltrials.gov/ct2/show/NCT04765436)

Safety and Efficacy of Preventative COVID Vaccines: The StopCoV Study (preprint)

Background: To partially immunize more persons against COVID-19 during a time of limited vaccine availability, Canadian public health officials recommended extending the vaccine dose interval and brand mixing. Impact on the antibody response among the older ambulatory population was unclear. Methods: Decentralized prospective cohort study with self-report of adverse events and collection of dried blood spots. Data is presented for 1193 (93%) of the 911 older (aged >70 years) and 375 younger (30-50 years) recruits. Findings: Local and systemic reactivity rates were high but short-lived, particularly in the younger cohort and with mRNA-1273 vaccine. After a single COVID-19 vaccine, 84% younger but only 46% older participants had positive IgG antibodies to both spike protein and receptor binding domain (RBD) antigens, increasing to 100/98% with the second dose respectively. In multivariable linear regression model, lower normalized IgG RBD antibody ratios two weeks after the second dose were statistically associated with older age, male gender, cancer diagnosis, lower body weight, BNT162b2 relative to mRNA-1273 and longer dose intervals. Antibody ratios in both cohorts declined 12 weeks post second vaccine dose. Interpretation: We report success of a decentralized serology study. Antibody responses were higher in the younger than older cohort and were greater for those with at least one mRNA-1273 dose. The immunity threshold is unknown but correlations between binding and neutralizing antibodies are strongly positive. Trends with time and at breakthrough infection will inform vaccine booster strategies. Funding: Supported by the Public Health Agency of Canada and the University Health Network Foundation.

Antibody and T cell responses to SARS-CoV-2 mRNA vaccines during maintenance therapy for immune-mediated inflammatory diseases (preprint)

Background Limited information is available on the impact of immunosuppressants on COVID-19 vaccination in patients with immune-mediated inflammatory diseases (IMID). This study investigated antibody and T cell responses to SARS-CoV-2 mRNA vaccines in IMID patients undergoing immunomodulatory maintenance therapy. Methods This observational cohort study examined the immunogenicity of SARS-CoV-2 mRNA vaccines in adult patients with inflammatory bowel disease, rheumatoid arthritis, ankylosing spondylitis or psoriatic disease, with or without maintenance immunosuppressive therapies. T cell and antibody responses to SARS-COV-2, including neutralization against SARS-CoV-2 variants were determined pre-vaccination and after 1 and 2 vaccine doses. Findings We prospectively followed 150 subjects, 26 healthy controls, 9 IMID patients on no treatment, 44 on anti-TNF, 16 on anti-TNF with methotrexate/azathioprine (MTX/AZA), 10 on anti-IL-23, 28 on anti-IL-12/23, 9 on anti-IL-17, and 8 on MTX/AZA. Most patients showed increased antibody responses from dose 1 to dose 2, with decreases apparent by 3 months post dose 2, albeit with considerable variability within groups. Overall, T cell responses were not consistently different between groups; however, antibody levels and neutralization efficacy in the anti-TNF treated group was lower than controls and waned substantially by 3 months post-dose 2. Implications These findings support the need for a third dose of mRNA vaccine and for continued monitoring of immunity over time.

Longitudinal Assessment of SARS-CoV-2 Specific T Cell Cytokine-Producing Responses for 1 Year Reveals Persistence of Multi-Cytokine Proliferative Responses, with Greater Immunity Associated with Disease Severity (preprint)

Cellular-mediated immunity is critical for long-term protection against most viral infections, including coronaviruses. We studied 23 SARS-CoV-2-infected survivors over a one year post symptom onset (PSO) interval by ex vivo cytokine ELISpot assay. All subjects demonstrated SARS-CoV-2-specific IFN-{gamma}, IL-2, and Granzyme B (GzmB) T cell responses at presentation, with greater frequencies in severe disease. Cytokines, mainly produced by CD4+ T cells, targeted all structural proteins (Nucleocapsid, Membrane, Spike) except Envelope, with GzmB > IL-2 > IFN-{gamma}. Mathematical modeling predicted that: 1) cytokine responses peaked at 6 days for IFN-{gamma}, 36 days for IL-2, and 7 days for GzmB, 2) severe illness was associated with reduced IFN-{gamma} and GzmB, but increased IL-2 production rates, 3) males displayed greater production of IFN-{gamma}, whereas females produced more GzmB. Ex vivo responses declined over time with persistence of IL-2 in 86% and of IFN-{gamma} and GzmB in 70% of subjects at a median of 336 days PSO. The average half-life of SARS-CoV-2-specific cytokine-producing cells was modelled to be 139 days (~4.6 months). Potent T cell proliferative responses persisted throughout observation, were CD4 dominant, and were capable of producing all 3 cytokines. Several immunodominant CD4 and CD8 epitopes identified in this study were shared by seasonal coronaviruses or SARS-CoV-1 in the Nucleocapsid and Membrane regions. Both SARS-CoV-2-specific CD4+ and CD8+ T cell clones were able to kill target cells, though CD8 tended to be more potent.

Immunogenicity of convalescent and vaccinated sera against clinical isolates of ancestral SARS-CoV-2, beta, delta, and omicron variants (preprint)

The omicron variant of concern (VOC) of SARS-CoV-2 was first reported in November 2021 in Botswana and South Africa. Omicron variant has evolved multiple mutations within the spike protein and the receptor binding domain (RBD), raising concerns of increased antibody evasion. Here, we isolated infectious omicron from a clinical specimen obtained in Canada. The neutralizing activity of sera from 65 coronavirus disease (COVID-19) vaccine recipients and convalescent individuals against clinical isolates of ancestral SARS-CoV-2, beta, delta, and omicron VOCs was assessed. Convalescent sera from unvaccinated individuals infected by the ancestral virus during the first wave of COVID-19 in Canada (July, 2020) demonstrated reduced neutralization against beta, delta and omicron VOCs. Convalescent sera from unvaccinated individuals infected by the delta variant (May-June, 2021) neutralized omicron to significantly lower levels compared to the delta variant. Sera from individuals that received three doses of the Pfizer or Moderna vaccines demonstrated reduced neutralization of both delta and omicron variants relative to ancestral SARS-CoV-2. Sera from individuals that were naturally infected with ancestral SARS-CoV-2 and subsequently received two doses of the Pfizer vaccine induced significantly higher neutralizing antibody levels against ancestral virus and all VOCs. Importantly, infection alone, either with ancestral SARS-CoV-2 or the delta variant was not sufficient to induce high neutralizing antibody titers against omicron. This data will inform current booster vaccination strategies and we highlight the need for additional studies to identify longevity of immunity against SARS-CoV-2 and optimal neutralizing antibody levels that are necessary to prevent infection and/or severe COVID-19.

A "Made-in-Canada" serology solution for profiling humoral immune responses to SARS-CoV-2 infection and vaccination (preprint)

BACKGROUND: Testing for antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been instrumental in detecting previous exposures and analyzing vaccine-elicited immune responses. Here, we describe a scalable "Made-in-Canada" solution that can detect and quantify SARS-CoV-2 antibodies, discriminate between natural infection- and vaccination-induced responses, and assess antibody-mediated inhibition of the spike-angiotensin converting enzyme 2 (ACE2) interaction. METHODS: We developed a set of methods and reagents to detect SARS-CoV-2 antibodies by enzyme-linked immunosorbent assay (ELISA). The main assays focus on the parallel detection of immunoglobulin (Ig)Gs against the spike trimer, its receptor binding domain (RBD), and the nucleocapsid (N) protein. These antigens are complemented by a detection antibody (human anti-IgG fused to horseradish peroxidase (HRP)) and a positive control reference antibody (recombinant IgG against the RBD), permitting intra- and inter-laboratory comparisons. Using this toolkit and commercial reagents, we optimized automated ELISAs on two different high throughput platforms to measure antibody responses to SARS-CoV-2 antigens. The assays were calibrated to a reference standard from the World Health Organization. We also automated a surrogate neutralization (sn)ELISA that measures inhibition of ACE2-Spike or -RBD interactions by antibodies using biotinylated ACE2. RESULTS: Our individual IgG-based ELISAs measure antibody levels in single-point measurements in reference to a standard antibody curve to accurately distinguish non-infected and infected individuals (area under the curve > 0.96 for each assay). Positivity thresholds can be established in individual assays using precision-recall analysis (e.g., by fixing the false positive rate), or more stringently, by scoring against the distribution of the means of negative samples across multiple assays performed over several months. For seroprevalence assessment (in a non-vaccinated cohort), classifying a sample as positive if antibodies were detected for at least 2 of the 3 antigens provided the highest specificity. In vaccinated cohorts, increases in anti-spike and -RBD (but not -N) antibodies are observed. Here, we present detailed protocols to perform these assays using either serum/plasma or dried blood spots both manually and on two automated platforms, and to express the results in international units to facilitate data harmonization and inter-study comparisons. We also demonstrate that the snELISA can be performed automatically at single points, increasing the scalability of this functional assay for large seroprevalence studies. INTERPRETATION: The ability to measure antibodies to three viral antigens and identify neutralizing antibodies capable of disrupting spike-ACE2 interactions in high-throughput assays enables large-scale analyses of humoral immune responses to SARS-CoV-2 infection and vaccination. The "Made-in-Canada" set of protein reagents, produced at the National Research Council of Canada are publicly available to enable the up-scaling of standardized serological assays, permitting nationwide data comparison and aggregation.

Intramuscular SARS-CoV-2 vaccines elicit varying degrees of plasma and salivary antibody responses as compared to natural infection (preprint)

Vaccination induced antibody and T-cell immune responses are important for systemic protection from COVID-19. Because SARS-CoV-2 infects and is transmitted by oral-pharyngeal mucosa, we wished to test mucosal antibodies elicited by natural infection or intramuscular vaccine injection. In a non-randomized observational study, we measured antibodies against the SARS-CoV-2 RBD in plasma and saliva from convalescent or vaccinated individuals and tested their neutralizing potential using a replication competent rVSV-eGFP-SARS-CoV-2. We found IgG and IgA anti-RBD antibodies as well as neutralizing activity in convalescent plasma and saliva. Two doses of mRNA vaccination (BNT162b2 or mRNA-1273) induced high levels of IgG anti-RBD in saliva, a subset of whom also had IgA, and significant neutralizing activity. We detected anti-RBD IgG and IgA with significant neutralizing potential in the plasma of single dose Ad26.COV2.S vaccinated individuals, and we detected slight amounts of anti-RBD antibodies in matched saliva. The role of salivary antibodies in protection against SARS-CoV-2 infection is unknown and merits further investigation. This study was not designed to, nor did it study the full kinetics of the antibody response or protection from infection, nor did it address variants of SARS-CoV-2.

Neutralizing antibody responses to SARS-CoV-2 variants in vaccinated Ontario long-term care home residents and workers (preprint)

Prioritizing Ontarios long-term care home (LTCH) residents for vaccination against severe acute respiratory syndrome coronavirus 2 has drastically reduced their disease burden; however, recent LTCH outbreaks of variants of concern (VOCs) have raised questions regarding their immune responses. In 198 residents, mRNA vaccine dose 1 elicited partial spike and receptor binding domain antibody responses, while the second elicited a response at least equivalent to convalescent individuals in most residents. Residents administered mRNA-1273 (Moderna) mounted stronger total and neutralizing antibody responses than those administered BNT162b2 (Pfizer-BioNTech). Two to four weeks after dose 2, residents (n = 119, median age 88) produced 4.8-6.3-fold fewer neutralizing antibodies than staff (n = 78; median age 47) against wild-type (with D614G) pseudotyped lentivirus, and residents administered BNT162b2 produced 3.89-fold fewer neutralizing antibodies than those who received mRNA-1273. These effects were exacerbated upon serum challenge with pseudotyped VOC spike, with up to 7.94-fold reductions in B.1.351 (Beta) neutralization. Cumulatively, weaker vaccine stimulation, age/comorbidities, and the VOC produced an [~]130-fold reduction in apparent neutralization titers in LTCH residents and 37.9% of BNT162b2-vaccinated residents had undetectable neutralizing antibodies to B.1.351. Continued immune response surveillance and additional vaccine doses may be required in this population with known vulnerabilities.

A mucosal antibody response is induced by intra-muscular SARS-CoV-2 mRNA vaccination (preprint)

The first line of defense against SARS-CoV-2 is the upper respiratory tract, yet we know little about the amount, type, and kinetics of mucosal anti-Spike antibodies (Ab) in response to intramuscular (i.m.) COVID-19 vaccination. We analyzed salivary Ab against SARS-CoV-2 Spike following mRNA/mRNA and adenovirus (Ad)/mRNA regimes. While anti-Spike/RBD IgG was detected in the saliva and correlated with the systemic response, anti-Spike/RBD IgA associated with the secretory component (sIgA) was also detected, and did not necessarily correlate with serum Ab. Only modest levels of neutralizing capacity were observed in saliva at 2 weeks post-dose 2, and by 6 months, anti-Spike/RBD IgG were greatly diminished. In contrast, low levels of anti-Spike sIgA persisted up to 6 months after dose 2. Our results show that SARS-CoV-2 vaccination induces an IgG response in the saliva that decays over time and an sIgA response that does not necessarily correlate with systemic immunity. One-Sentence SummaryOur study delves into how intra-muscular mRNA/mRNA or mRNA/Ad COVID-19 vaccination regimes confer immunity in the oral cavity with important implications for understanding protection against breakthrough infections in healthy vaccinated people.

Immunity to SARS-CoV-2 persists 9 months post-symptoms with an altered T cell phenotype compared to influenza A virus-specific memory (preprint)

SARS-CoV-2 induces T cell, B cell and antibody responses that are detected for several months in recovered individuals. Whether this response resembles a typical respiratory viral infection is a matter of debate. Here we followed T cell and antibody responses in 24 mainly non-hospitalized SARS-CoV-2 recovered subjects at two time points (median of 45- and 145-days post-symptom onset). Antibody responses were detected in 95% of subjects, with a strong correlation between plasma and salivary anti-S and anti-RBD IgG, as well as a correlation between circulating T follicular helper cells and the SARS-CoV-2-specific IgG response. Based on intracellular cytokine production or proliferation, CD4+ T cell responses to SARS-CoV-2 were detected in all subjects, decaying with a half-life of 5-6 months for S-specific IL-2-producing cells. CD4+ responses were largely of the T helper 1 phenotype, but with a lower ratio of IFN-{gamma} : IL-2 producing cells and a lower frequency of CD8+: CD4+ T cells compared to influenza A virus-(IAV)-specific memory responses within the same subjects. Analysis of secreted molecules also revealed a lower ratio of IFN-{gamma}: IL-2 and IFN-{gamma}: IL-6 and an altered cytotoxic profile for S- and N-specific compared to IAV-specific responses. These data suggest that the memory T-cell phenotype after a single infection with SARS-CoV-2 persists over time, with an altered cytokine and cytotoxic profile compared to long term memory to IAV within the same subjects.