Titers of Neutralizing Antibodies against SARS-CoV-2 Are Independent of Symptoms of Non-Severe COVID-19 in Young Adults

Dynamics of anti-SARS-CoV-2 IgG antibody responses following breakthrough infection and the predicted protective efficacy: A longitudinal community-based population study in China

OBJECTIVES

To assess the dynamics of the anti-SARS-CoV-2 IgG antibody levels and their efficacy against COVID-19.

METHODS

We conducted a longitudinal serological analysis of 852 breakthrough COVID-19 infections among the community-based population in Yichang, China. Anti-SARS-CoV-2 IgG levels were measured by chemiluminescence at approximately 3, 4, and 9 months after infection. A linear mixed model predicted IgG antibody decline over 18 months. The effectiveness of antibodies in preventing symptomatic and severe infections was determined using an existing meta-regression model.

RESULTS

IgG antibodies slowly declined after breakthrough infections. Initially high at around 3 months (339.44 AU/mL, IQR: 262.78-382.95 AU/mL), levels remained significant at 9 months (297.74 AU/mL, IQR: 213.22-360.62 AU/mL). The elderly (≥60 years) had lower antibody levels compared to the young (<20 years) (P < 0.001). The protective efficacy of antibodies against symptomatic and severe infections was lower in the elderly (≥60 years) (78.34% and 86.33%) compared to the young (<20 years) (96.56% and 98.75%) after 1 year.

CONCLUSION

The study indicated a slow decline in anti-SARS-CoV-2 IgG antibodies, maintaining considerable efficacy for over 1 year. However, lower levels in the elderly suggest reduced protective effects, underscoring the need for age-specific vaccination strategies.

Factors influencing the immune response over 15 months after SARS-CoV-2 infection: A longitudinal population-wide study in the Faroe Islands

BACKGROUND

The durability of SARS-CoV-2 antibody response and the resulting immunity to COVID-19 is unclear.

OBJECTIVES

To investigate long-term humoral immunity to SARS-CoV-2.

METHODS

In this nationwide, longitudinal study, we determined antibody response in 411 patients aged 0-93 years from two waves of infections (March to December 2020) contributing 1063 blood samples. Each individual had blood drawn on 4-5 occasions 1-15 months after disease onset. We measured total anti-SARS-CoV-2 receptor-binding domain (RBD) antibody using a qualitative RBD sandwich ELISA, IgM, IgG and IgA levels using an quantitative in-house ELISA-based assay  and neutralizing antibodies (NAbs) using an in-house ELISA-based pseudoneutralizing assay. IgG subclasses were analyzed in a subset of samples by ELISA-based assay. We used nonlinear models to study the durability of SARS-CoV-2 antibody responses and its influence over time.

RESULTS

After 15 months, 94% still had detectable circulating antibodies, mainly the IgG isotype, and 92% had detectable NAbs. The distribution of IgG antibodies varied significantly over time, characterized by a biphasic pattern with an initial decline followed by a plateau after approximately 7 months. However, the NAbs remained relatively stable throughout the period. The strength of the antibody response was influenced by smoking and hospitalization, with lower IgG levels in smokers and higher levels in hospitalized individuals. Antibody stability over time was mainly associated with male sex and older age with higher initial levels but more marked decrease.

CONCLUSIONS

The humoral immune response to SARS-CoV-2 infection varies depending on behavioral factors and disease severity, and antibody stability over 15 months was associated with sex and age.

Persistence, prevalence, and polymorphism of sequelae after COVID-19 in unvaccinated, young adults of the Swiss Armed Forces: a longitudinal, cohort study (LoCoMo)

BACKGROUND

Persistent COVID-19 sequelae could have global, public health ramifications. We therefore aimed to describe sequelae presenting more than 180 days after COVID-19-focussing on several organ systems, general health, and laboratory parameters-in non-hospitalised, unvaccinated, young adults.

METHODS

We did a longitudinal cohort study of all army bases in Switzerland. Eligible participants were personnel of the Swiss Armed Forces (SAF) who were aged 18-30 years with a positive or negative RT-PCR test for SARS-CoV-2 during their service between March 1, 2020, and Dec 31, 2020. Exclusion criteria were unwillingness to participate in testing. Females or men with a known reproductive anomaly were excluded from the optional component of male fertility testing. COVID-19 was defined as a positive diagnostic RT-PCR test result for SARS-CoV-2 with concurrent symptoms compatible with COVID-19. Participants were subdivided into four groups: control group (ie, serologically negative), asymptomatic infection group (ie, serologically positive but with no symptoms), non-recent COVID-19 group (>180 days since positive PCR test), and recent COVID-19 group (≤180 days since positive PCR test). Outcomes of interest were part of a comprehensive, intensive test battery that was administered during a single day. The test battery quantified the effect of SARS-CoV-2 infection on cardiovascular, pulmonary, neurological, renal, ophthalmological, male reproductive, psychological, general health, and laboratory parameters. This study was registered with ClinicalTrials.gov, number NCT04942249.

FINDINGS

Between May 20, 2021, and Nov 26, 2021, we enrolled 501 participants. 29 (6%) of 501 were female and 464 (93%) were male, and the median age was 21 years (IQR 21-23). Eight (2%) of 501 had incomplete data and were not included into the study groups. 177 participants had previous COVID-19 that was more than 180 days (mean 340 days) since diagnosis (ie, the non-recent COVID-19 group) compared with 251 serologically negative individuals (ie, the control group). We included 19 participants in the recent COVID-19 group and 46 in the asymptomatic infection group. We found a significant trend towards metabolic disorders in participants of the non-recent COVID-19 group compared with those in the control group: higher BMI (median 24·0 kg/m² [IQR 22·0-25·8] vs 23·2 kg/m² [27·1-25·0]; p=0·035), lower aerobic threshold (39% [36-43] vs 41% [37-46]; p=0·012), and higher blood cholesterol (4·2 μM [3·7-4·7] vs 3·9 μM [3·5-4·5]; p<0·0001) and LDL concentrations (2·4 μM [1·9-2·9] vs 2·2 μM [1·7-2·7]; p=0·001). The only significant psychosocial difference was found in the results of the Chalder Fatigue scale with the non-recent COVID-19 group reporting higher fatigue scores than the control group (median 12 points [IQR 11-15] vs 11 [9-14]; p=0·027). No significant differences in other psychosocial questionnaire scores, ophthalmological outcomes, and sperm quality or motility were reported between the control group and non-recent COVID-19 group.

INTERPRETATION

Young, previously healthy, individuals largely recover from SARS-CoV-2 infection. However, the constellation of higher BMI, dyslipidaemia, and lower physical endurance 180 days after COVID-19 is suggestive of a higher risk of developing metabolic disorders and possible cardiovascular complications. These findings will guide future investigations and follow-up management.

FUNDING

Swiss Armed Forces.

Sustained seropositivity up to 20.5 months after COVID-19

This study evaluated the persistence of IgM, IgA, and IgG to SARS-CoV-2 spike and nucleocapsid antigens up to 616 days since the onset of symptoms in a longitudinal cohort of 247 primary health care workers from Barcelona, Spain, followed up since the start of the pandemic. The study also assesses factors affecting antibody levels, including comorbidities and the responses to variants of concern as well as the frequency of reinfections. Despite a gradual and significant decline in antibody levels with time, seropositivity to five SARS-CoV-2 antigens combined was always higher than 90% over the whole study period. In a subset of 23 participants who had not yet been vaccinated by November 2021, seropositivity remained at 95.65% (47.83% IgM, 95.65% IgA, 95.65% IgG). IgG seropositivity against Alpha and Delta predominant variants was comparable to that against the Wuhan variant, while it was lower for Gamma and Beta (minority) variants and for IgA and IgM. Antibody levels at the time point closest to infection were associated with age, smoking, obesity, hospitalization, fever, anosmia/hypogeusia, chest pain, and hypertension in multivariable regression models. Up to 1 year later, just before the massive roll out of vaccination, antibody levels were associated with age, occupation, hospitalization, duration of symptoms, anosmia/hypogeusia, fever, and headache. In addition, tachycardia and cutaneous symptoms associated with slower antibody decay, and oxygen supply with faster antibody decay. Eight reinfections (3.23%) were detected in low responders, which is consistent with a sustained protective role for anti-spike naturally acquired antibodies. Stable persistence of IgG and IgA responses and cross-recognition of the predominant variants circulating in the 2020-2021 period indicate long-lasting and largely variant-transcending humoral immunity in the initial 20.5 months of the pandemic, in the absence of vaccination.

Promotion of neutralizing antibody-independent immunity to wild-type and SARS-CoV-2 variants of concern using an RBD-Nucleocapsid fusion protein

Both T cells and B cells have been shown to be generated after infection with SARS-CoV-2 yet protocols or experimental models to study one or the other are less common. Here, we generate a chimeric protein (SpiN) that comprises the receptor binding domain (RBD) from Spike (S) and the nucleocapsid (N) antigens from SARS-CoV-2. Memory CD4⁺ and CD8⁺ T cells specific for SpiN could be detected in the blood of both individuals vaccinated with Coronavac SARS-CoV-2 vaccine and COVID-19 convalescent donors. In mice, SpiN elicited a strong IFN-γ response by T cells and high levels of antibodies to the inactivated virus, but not detectable neutralizing antibodies (nAbs). Importantly, immunization of Syrian hamsters and the human Angiotensin Convertase Enzyme-2-transgenic (K18-ACE-2) mice with Poly ICLC-adjuvanted SpiN promotes robust resistance to the wild type SARS-CoV-2, as indicated by viral load, lung inflammation, clinical outcome and reduction of lethality. The protection induced by SpiN was ablated by depletion of CD4⁺ and CD8⁺ T cells and not transferred by antibodies from vaccinated mice. Finally, vaccination with SpiN also protects the K18-ACE-2 mice against infection with Delta and Omicron SARS-CoV-2 isolates. Hence, vaccine formulations that elicit effector T cells specific for the N and RBD proteins may be used to improve COVID-19 vaccines and potentially circumvent the immune escape by variants of concern.

Protection against SARS-CoV-2 infection involves T cell and B cell responses but only studying one or the other has proved difficult. Here the authors immunise with a fusion protein construct of N and RBD proteins from SARS-CoV-2 and find that this promotes protection in animal models preferentially via T cells.

Prevalence and determinants of SARS-CoV-2 neutralizing antibodies in Lebanon

According to the Lebanese Ministry of Public Health, more than 1,053,000 cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection have been confirmed in Lebanon so far. The actual number of cases is likely to be higher. We conducted a serological study from October 2020 to April 2021 to estimate the prevalence of SARS-CoV-2 neutralizing antibodies and identify associated factors. Serum samples as well as demographic, health, and behavioral data were collected from 2,783 subjects. Sera were tested by microneutralization assay. Neutralizing antibodies were detected in 58.9% of the study population. The positivity rate increased over the study period. It was highest among the group who remained at work during the COVID-19 pandemic and in peri-urban areas with limited adherence to preventive measures. Sex and age were associated with positivity. Reported previous COVID-19, exposure to a COVID-19 patient in the family, and attending gatherings were associated with increased prevalence. Not taking any precautionary measures against COVID-19 was a risk factor, whereas precautionary measures such as working from home and washing hands were protective. The high neutralizing antibody seroprevalence rates detected in this study emphasize the high transmission rate of SARS-CoV-2 infection in the community. Adherence to preventive measures and non-pharmaceutical interventions imposed by the government is recommended.

Population differences in antibody response to SARS-CoV-2 infection and BNT162b2 vaccination

The concentration of SARS‐CoV‐2‐specific serum antibodies, elicited by vaccination or infection, is a primary determinant of anti‐viral immunity, which correlates with protection against infection and COVID‐19. Serum samples were obtained from 25 897 participants and assayed for anti‐SARS‐CoV‐2 spike protein RBD IgG antibodies. The cohort was composed of newly vaccinated BNT162b2 recipients, in the first month or 6 months after vaccination, COVID‐19 patients and a general sample of the Israeli population. Antibody levels of BNT162b2 vaccine recipients were negatively correlated with age, with a prominent decrease in recipients over 55 years old, which was most significant in males. This trend was observable within the first month and 6 months after vaccination, while younger participants were more likely to maintain stable levels of serum antibodies. The antibody concentration of participants previously infected with SARS‐CoV‐2 was lower than the vaccinated and had a more complex, non‐linear relation to age, sex and COVID‐19 symptoms. Taken together, our data supports age and sex as primary determining factors for both the magnitude and durability of humoral response to SARS‐CoV‐2 infection and the COVID‐19 vaccine. Our results could inform vaccination policies, prioritizing the most susceptible populations for repeated vaccination.

Current Potential Therapeutic Approaches against SARS-CoV-2: A Review

The ongoing SARS-CoV-2 pandemic is a serious threat to public health worldwide and, to date, no effective treatment is available. Thus, we herein review the pharmaceutical approaches to SARS-CoV-2 infection treatment. Numerous candidate medicines that can prevent SARS-CoV-2 infection and replication have been proposed. These medicines include inhibitors of serine protease TMPRSS2 and angiotensin converting enzyme 2 (ACE2). The S protein of SARS-CoV-2 binds to the receptor in host cells. ACE2 inhibitors block TMPRSS2 and S protein priming, thus preventing SARS-CoV-2 entry to host cells. Moreover, antiviral medicines (including the nucleotide analogue remdesivir, the HIV protease inhibitors lopinavir and ritonavir, and wide-spectrum antiviral antibiotics arbidol and favipiravir) have been shown to reduce the dissemination of SARS-CoV-2 as well as morbidity and mortality associated with COVID-19.

Responses to SARS-CoV-2 Vaccination in Patients with Cancer (ReCOVer Study): A Prospective Cohort Study of the Hellenic Cooperative Oncology Group

Data on the effectiveness and safety of approved SARS-CoV-2 vaccines in cancer patients are limited. This observational, prospective cohort study investigated the humoral immune response to SARS-CoV-2 vaccination in 232 cancer patients from 12 HeCOG-affiliated oncology departments compared to 100 healthcare volunteers without known active cancer. The seropositivity rate was measured 2-4 weeks after two vaccine doses, by evaluating neutralising antibodies against the SARS-CoV-2 spike protein using a commercially available immunoassay. Seropositivity was defined as ≥33.8 Binding-Antibody-Units (BAU)/mL. A total of 189 patients and 99 controls were eligible for this analysis. Among patients, 171 (90.5%) were seropositive after two vaccine doses, compared to 98% of controls (p = 0.015). Most seronegative patients were males (66.7%), >70-years-old (55.5%), with comorbidities (61.1%), and on active treatment (88.9%). The median antibody titers among patients were significantly lower than those of the controls (523 vs. 2050 BAU/mL; p < 0.001). The rate of protective titers was 54.5% in patients vs. 97% in controls (p < 0.001). Seropositivity rates and IgG titers in controls did not differ for any studied factor. In cancer patients, higher antibody titers were observed in never-smokers (p = 0.006), women (p = 0.022), <50-year-olds (p = 0.004), PS 0 (p = 0.029), and in breast or ovarian vs. other cancers. Adverse events were comparable to registration trials. In this cohort study, although the seropositivity rate after two vaccine doses in cancer patients seemed satisfactory, their antibody titers were significantly lower than in controls. Monitoring of responses and further elucidation of the clinical factors that affect immunity could guide adaptations of vaccine strategies for vulnerable subgroups.

Neutralizing antibody response to SARS-CoV-2 persists 9 months post symptom onset in mild and asymptomatic patients

Objective

A better understanding of the immune response against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection is critical to predict its dynamics within the general population and its impact on the vaccination strategy. This study assessed the persistence of neutralizing antibody (Nab) activity and SARS-CoV-2 serology in serum samples of mild and asymptomatic patients 9 months post symptom onset (PSO) in a primary care context among immunocompetent adults.

Methods

A longitudinal cohort of crew members (CMs) exposed to coronavirus disease 2019 (COVID-19) during an outbreak of SARS-CoV-2 on the French aircraft carrier ‘Charles de Gaulle’ in April 2020 was created. CMs infected with COVID-19 and with positive serology at the end of quarantine were tested 9 months PSO. Samples were collected 18 and 280 days PSO. For each patient, both serology and serum viral neutralizing activity were performed.

Results

In total, 86 CMs were analysed. Samples were collected 18 and 280 days PSO. The seroconversion rates were 100% and 93% (82/86) at 18 and 280 days PSO, respectively, and 72.7% of patients exhibited persistent Nab activity at 9 months, regardless of disease severity.

Conclusion

Nab activity persists for up to 9 months following asymptomatic/mild COVID-19 among young adults, regardless of serological results.

Seroprevalence of SARS-CoV-2 Binding and Neutralizing Antibodies in Healthcare Workers during the Epidemic Peak in Referral Hospitals and Quarantine Sites: Saudi Arabia

Healthcare workers (HCWs) are at high risk for SARS-CoV-2 infection compared to the general population. Here, we aimed to evaluate and characterize the SARS-CoV-2 seropositivity rate in randomly collected samples among HCWs from the largest referral hospitals and quarantine sites during the peak of the COVID-19 epidemic in the city of Jeddah, the second largest city in Saudi Arabia, using a cross-sectional analytic study design. Out of 693 participants recruited from 29 June to 10 August 2020, 223 (32.2%, 95% CI: 28.8–35.8) were found to be confirmed seropositive for SARS-CoV-2 antibodies, and among those 197 (88.3%) had never been diagnosed with COVID-19. Seropositivity was not significantly associated with participants reporting COVID-19 compatible symptoms as most seropositive HCW participants 140 (62.8%) were asymptomatic. The large proportion of asymptomatic SARS-CoV-2 cases detected in our study demands periodic testing as a general hospital policy.

Persistence and baseline determinants of seropositivity and reinfection rates in health care workers up to 12.5 months after COVID-19

We assessed the duration and baseline determinants of antibody responses to SARS-CoV-2 spike antigens and the occurrence of reinfections in a prospective cohort of 173 Spanish primary health care worker patients followed initially for 9 months and subsequently up to 12.5 months after COVID-19 symptoms onset. Seropositivity to SARS-CoV-2 spike and receptor-binding domain antigens up to 149-270 days was 92.49% (90.17% IgG, 76.3% IgA, 60.69% IgM). In a subset of 64 health care workers who had not yet been vaccinated by April 2021, seropositivity was 96.88% (95.31% IgG, 82.81% IgA) up to 322-379 days post symptoms onset. Four suspected reinfections were detected by passive case detection, two among seronegative individuals (5 and 7 months after the first episode), and one low antibody responder. Antibody levels significantly correlated with fever, hospitalization, anosmia/hypogeusia, allergies, smoking, and occupation. Stable sustainment of IgG responses raises hope for long-lasting COVID-19 vaccine immunity.

Understanding COVID-19 Epidemiology and Implications for Control: The Experience from a Greek Semi-Closed Community

BACKGROUND

We aimed to estimate the SARS-CoV-2 antigen and antibody seroprevalence in one of the worst-affected by the pandemic semi-closed communities in Greece, Deskati, and evaluate the sociodemographic and clinical correlations of functional antibody responses.

METHODS

The Ag2019n-CoV V1310/V1330 Rapid Test (Prognosis Biotech, Greece) was used for antigen detection. The Rapid Test 2019-nCoV Total Ig, V1210/V1230 (Prognosis Biotech, Greece), and the SARS-CoV-2 IgG II Quant method (Architect, Abbott, Illinois, USA) were used for antibody testing.

RESULTS

None of the participants had a positive antigen result. SARS-CoV-2 seropositivity ranged from 13% to 45% in the study population, depending on the method. One-third of the participants with known past infection had a positive antibody test result 77 ± 13 days after infection. Two-fifths of infections determined by serology were asymptomatic. The advancing age and hospitalization predicted seropositivity among patients with past infection. Half of the participants who tested positive for antibodies were not aware of past infection.

CONCLUSIONS

High-burden contexts in Greece, such as Deskati, are not so far from herd immunity thresholds. We highlighted the value of low-cost serosurveys targeting both symptomatic and asymptomatic populations to evaluate the natural immune response to SARS-CoV-2 in nonvaccinated susceptibles and design evidence-based policies for lifting lockdowns.