Effect of vaccine booster, vaccine type, and hybrid immunity on humoral and cellular immunity against SARS-CoV-2 ancestral strain and Omicron variant sublineages BA.2 and BA.5 among older adults with comorbidities: a cross sectional study.

BACKGROUND: Vaccination reduces COVID-19-related hospitalization among older adults. However, how SARS-CoV-2 infection and vaccine regimens affect vaccine-elicited immunity remain unclear. METHODS: This is a cross-sectional study recruiting adults aged ≥70 years with comorbidities in Hong Kong. Demographic and clinical information were collected using a questionnaire. Neutralizing antibody (nAb) titers (against ancestral and Omicron strains) and SARS-CoV-2-specific T cell response were analyzed according to infection and vaccination status. Multivariable regression analysis was performed to assess the associations of BNT162b2 and booster doses with higher nAb titers, with adjustment for comorbidities. FINDINGS: In July 2022, 101 patients were recruited, of whom 25 (24%) had previous infection. Overall, the geometric mean titer (GMT) of BA.5 nAb was 2.8-fold lower than that against BA.2 (P < 0.0001). The ancestral strain and BA.2 titers were higher for the 3-4-dose-BNT162 group than the 2-dose-BNT162b2 group. Non-infected individuals in the 3-4-dose-CoronaVac group had a more robust T cell response than the 2-dose-CoronaVac group (P = 0.0181), but there was no significant difference between the 2-dose-BNT162b2 and 3-4-dose-BNT162b groups. Patients who had heterologous CoronaVac-BNT162b2 prime-boost regimen had 3.22-fold higher BA.5 nAb titers than those who were primed/boosted with CoronaVac (P = 0.0207). Patients with hybrid immunity had higher Omicron nAb titers than those with vaccine-only immunity. Multivariable analysis showed that BNT162b2 and booster doses were independently associated with higher ancestral strain nAb titers. INTERPRETATION: Our data support the use of booster doses for older adults with or without prior infection. Non-infected individuals primed with CoronaVac will benefit from heterologous mRNA vaccine booster. FUNDING: Richard and Carol Yu, May Tam Mak Mei Yin, The Shaw Foundation Hong Kong, Michael Tong, Marina Lee, Government Consultancy Service (See acknowledgements for full list).

SARS-CoV-2 IgG seropositivity after the severe Omicron wave of COVID-19 in Hong Kong.

The SARS-CoV-2 Omicron variant has led to a major wave of COVID-19 in Hong Kong between January and May 2022. Here, we used seroprevalence to estimate the combined incidence of vaccination and SARS-CoV-2 infection, including subclinical infection which were not diagnosed at the acute stage. The overall seropositive rate of IgG against receptor binding domain (anti-RBD IgG) increased from 52.2% in December 2021 to 89.3% in May 2022. The level of anti-RBD IgG was lowest in the 0-9 and ≥80 year-old age groups in May 2022. The seropositive rate of antibody against ORF8, which reflects the rate of prior infection, was 23.4% in May 2022. Our data suggest that although most individuals were either vaccinated or infected after the fifth wave, children and older adults remain most vulnerable. Public health measures should target these age groups in order to ameliorate the healthcare consequences of upcoming waves.

Boosting of serum neutralizing activity against the Omicron variant among recovered COVID-19 patients by BNT162b2 and CoronaVac vaccines.

BACKGROUND: SARS-CoV-2 Omicron variant evades immunity from past infection or vaccination and is associated with a greater risk of reinfection among recovered COVID-19 patients. We assessed the serum neutralizing antibody (NAb) activity against Omicron variant (Omicron NAb) among recovered COVID-19 patients with or without vaccination. METHODS: In this prospective cohort study with 135 recovered COVID-19 patients, we determined the serum NAb titers against ancestral virus or variants using a live virus NAb assay. We used the receiver operating characteristic analysis to determine the optimal cutoff for a commercially-available surrogate NAb assay. FINDINGS: Among recovered COVID-19 patients, the serum live virus geometric mean Omicron NAb titer was statistically significantly higher among BNT162b2 recipients compared to non-vaccinated individuals (85.4 vs 5.6,P < 0.0001). The Omicron seropositive rates in live virus NAb test (NAb titer ≥10) were statistically significantly higher among BNT162b2 (90.6% [29/32];P < 0.0001) or CoronaVac (36.7% [11/30]; P = 0.0115) recipients when compared with non-vaccinated individuals (12.3% [9/73]). Subgroup analysis of CoronaVac recipients showed that the Omicron seropositive rates were higher among individuals with two doses than those with one dose (85.7% vs 21.7%; P = 0.0045). For the surrogate NAb assay, a cutoff of 109.1 AU/ml, which is 7.3-fold higher than the manufacturer's recommended cutoff, could achieve a sensitivity and specificity of 89.5% and 89.8%, respectively, in detecting Omicron NAb. INTERPRETATION: Among individuals with prior COVID-19, one dose of BNT162b2 or two doses of CoronaVac could induce detectable serum Omicron NAb. Our result would be particularly important for guiding vaccine policies in countries with COVID-19 vaccine shortage. FUNDING: Health and Medical Research Fund, Richard and Carol Yu, Michael Tong (see acknowledgments for full list).

Correlation between Commercial Anti-RBD IgG Titer and Neutralization Titer against SARS-CoV-2 Beta Variant.

OBJECTIVES: The emergence of SARS-CoV-2 variants of concern (VOCs) have diminished the effectiveness of vaccines and are associated with a rebound in the number of COVID-19 cases globally. These variants contain mutations at the spike (S) protein receptor binding site (RBD), which affect antibody binding. Current commercially available antibody assays were developed before the VOCs emerged. It is unclear whether the levels of these commercially available antibody assays can predict the neutralizing antibody titers against the VOCs. In this study, we sought to determine the correlation between the binding antibody concentration and microneutralization antibody titer against the beta variant. METHODS: This study included 58 COVID-19 patients. The concentrations of IgG against the SARS-CoV-2 spike protein RBD and nucleocapsid (N) protein were measured using the Abbott SARS-CoV-2 IgG II Quant assay and the SARS-CoV-2 IgG assay, respectively. The neutralization antibody titer against the wild type lineage A SARS-CoV-2 and against the beta variant (B.1.351) was determined using a conventional live virus neutralization test. RESULTS: The geometric mean MN titer (GMT) against the beta variant was significantly lower than that against the wild type lineage A virus (5.6 vs. 47.3, p < 0.0001). The anti-RBD IgG had a better correlation with the neutralizing antibody titer than that of the anti-N IgG assay against the wild type lineage A virus (Spearman rho, 0.5901 vs. 0.3827). However, the correlation between the anti-RBD or the anti-N IgG and the MN titer against the beta variant was poor. CONCLUSIONS: Currently available commercial antibody assays may not predict the level of neutralizing antibodies against the variants. A new generation of antibody tests specific for variants are required.

Coronavirus Disease 2019 (COVID-19) Re-infection by a Phylogenetically Distinct Severe Acute Respiratory Syndrome Coronavirus 2 Strain Confirmed by Whole Genome Sequencing.

BACKGROUND: Waning immunity occurs in patients who have recovered from Coronavirus Disease 2019 (COVID-19). However, it remains unclear whether true re-infection occurs. METHODS: Whole genome sequencing was performed directly on respiratory specimens collected during 2 episodes of COVID-19 in a patient. Comparative genome analysis was conducted to differentiate re-infection from persistent viral shedding. Laboratory results, including RT-PCR Ct values and serum Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) IgG, were analyzed. RESULTS: The second episode of asymptomatic infection occurred 142 days after the first symptomatic episode in an apparently immunocompetent patient. During the second episode, there was evidence of acute infection including elevated C-reactive protein and SARS-CoV-2 IgG seroconversion. Viral genomes from first and second episodes belong to different clades/lineages. The virus genome from the first episode contained a a stop codon at position 64 of ORF8, leading to a truncation of 58 amino acids. Another 23 nucleotide and 13 amino acid differences located in 9 different proteins, including positions of B and T cell epitopes, were found between viruses from the first and second episodes. Compared to viral genomes in GISAID, the first virus genome was phylogenetically closely related to strains collected in March/April 2020, while the second virus genome was closely related to strains collected in July/August 2020. CONCLUSIONS: Epidemiological, clinical, serological, and genomic analyses confirmed that the patient had re-infection instead of persistent viral shedding from first infection. Our results suggest SARS-CoV-2 may continue to circulate among humans despite herd immunity due to natural infection. Further studies of patients with re-infection will shed light on protective immunological correlates for guiding vaccine design.

Repurposing of Miltefosine as an Adjuvant for Influenza Vaccine.

We previously reported that topical imiquimod can improve the immunogenicity of the influenza vaccine. This study investigated another FDA-approved drug, miltefosine (MTF), as a vaccine adjuvant. Mice immunized with an influenza vaccine with or without MTF adjuvant were challenged by a lethal dose of influenza virus 3 or 7 days after vaccination. Survival, body weight, antibody response, histopathological changes, viral loads, cytokine levels, and T cell frequencies were compared. The MTF-adjuvanted vaccine (MTF-VAC) group had a significantly better survival rate than the vaccine-only (VAC) group, when administered 3 days (80% vs. 26.7%, p = 0.0063) or 7 days (96% vs. 65%, p = 0.0041) before influenza virus challenge. Lung damage was significantly ameliorated in the MTF-VAC group. Antibody response was significantly augmented in the MTF-VAC group against both homologous and heterologous influenza strains. There was a greater T follicular helper cell (TFH) response and an enhanced germinal center (GC) reaction in the MTF-VAC group. MTF-VAC also induced both TH1 and TH2 antigen-specific cytokine responses. MTF improved the efficacy of the influenza vaccine against homologous and heterologous viruses by improving the TFH and antibody responses. Miltefosine may also be used for other vaccines, including the upcoming vaccines for COVID-19.

Seroprevalence of SARS-CoV-2 in Hong Kong and in residents evacuated from Hubei province, China: a multicohort study.

BACKGROUND: The role of subclinical severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in perpetuating the COVID-19 pandemic is unknown because population seroprevalence data are absent. We aimed to establish the sensitivity and specificity of our enzyme immunoassay and microneutralisation assay, and the seroprevalence of SARS-CoV-2 in Hong Kong before and after the pandemic, as well as in Hong Kong residents evacuated from Hubei province, China. METHODS: We did a multicohort study in a hospital and university in Hong Kong. We evaluated the sensitivity of our enzyme immunoassay and microneutralisation assay with RT-PCR data from patients positive for SARS-CoV-2 and the specificity of our enzyme immunoassay and microneutralisation assay with archived serum samples collected before 2019. We compared the seropositivity of the general population of Hong Kong before and after the pandemic had begun, and determined the seropositivity of Hong Kong residents evacuated from Hubei province, China, in March, 2020. FINDINGS: Between Feb 26 and March 18, 2020, we assessed RT-PCR samples from 45 patients who had recovered from COVID-19 to establish the sensitivity of our enzyme immunoassay and microneutralisation assay. To establish the specificity of these assays, we retrieved archived serum. The sensitivity was 91·1% (41 of 45 [95% CI 78·8-97·5]) for the microneutralisation assay, 57·8% (26 of 45 [42·2-72·3]) for anti-nucleoprotein IgG, 66·7% (30 of 45 [51·1-80·0]) for anti-spike protein receptor binding domain (RBD) IgG, and 73·3% (33 of 45 [58·1-85·4]) for enzyme immunoassay (either positive for anti-nucleoprotein or anti-RBD IgG). The specificity was 100% (152 of 152 [95% CI 97·6-100·0]) for both the enzyme immunoassay and microneutralisation assay. Among the Hong Kong general population, 53 (2·7%) of 1938 were enzyme immunoassay positive, but of those who were positive, all 53 were microneutralisation negative, and no significant increase was seen in the seroprevalence between April 12, 2018, and Feb 13, 2020. Among asymptomatic Hubei returnees, 17 (4%) of 452 were seropositive with the enzyme immunoassay or the microneutralisation assay, with 15 (88%) of 17 seropositive with the microneutralisation assay, and two familial clusters were identified. INTERPRETATION: Our serological data suggest that SARS-CoV-2 is a new emerging virus. The seropositivity rate in Hubei returnees indicates that RT-PCR-confirmed patients only represent a small proportion of the total number of cases. The low seroprevalence suggests that most of the Hong Kong and Hubei population remain susceptible to COVID-19. Future waves of the outbreak are inevitable without a vaccine or antiviral prophylaxis. The role of age-related cross reactive non-neutralising antibodies in the pathogenesis of COVID-19 warrants further investigation. FUNDING: Richard and Carol Yu, May Tam Mak Mei Yin, Shaw Foundation (Hong Kong), Michael Tong, Marina Lee, and the Government Consultancy Service (see acknowledgments for full list).

Improved Detection of Antibodies against SARS-CoV-2 by Microsphere-Based Antibody Assay.

Currently available COVID-19 antibody tests using enzyme immunoassay (EIA) or immunochromatographic assay have variable sensitivity and specificity. Here, we developed and evaluated a novel microsphere-based antibody assay (MBA) for detecting immunoglobulin G (IgG) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein (NP) and spike protein receptor binding domain (RBD). The seropositive cutoff value was set using a cohort of 294 anonymous serum specimens collected in 2018. The specificity was assessed using serum specimens collected from organ donors or influenza patients before 2020. Seropositive rate was determined among COVID-19 patients. Time-to-seropositivity and signal-to-cutoff (S/CO) ratio were compared between MBA and EIA. MBA had a specificity of 100% (93/93; 95% confidence interval (CI), 96-100%) for anti-NP IgG, 98.9% (92/93; 95% CI 94.2-100%) for anti-RBD IgG. The MBA seropositive rate for convalescent COVID-19 patients was 89.8% (35/39) for anti-NP IgG and 79.5% (31/39) for anti-RBD IgG. The time-to-seropositivity was shorter with MBA than EIA. MBA could better differentiate between COVID-19 patients and negative controls with higher S/CO ratio for COVID-19 patients, lower S/CO ratio with negative controls and fewer specimens in the equivocal range. MBA is robust, simple and is suitable for clinical microbiology laboratory for the accurate determination of anti-SARS-CoV-2 antibodies for diagnosis, serosurveillance, and vaccine trials.

High neutralizing antibody titer in intensive care unit patients with COVID-19.

Coronavirus disease 2019 (COVID-19) has a wide spectrum of disease severity from mild upper respiratory symptoms to respiratory failure. The role of neutralizing antibody (NAb) response in disease progression remains elusive. This study determined the seroprevalence of 733 non-COVID-19 individuals from April 2018 to February 2020 in the Hong Kong Special Administrative Region and compared the neutralizing antibody (NAb) responses of eight COVID-19 patients admitted to the intensive care unit (ICU) with those of 42 patients not admitted to the ICU. We found that NAb against SARS-CoV-2 was not detectable in any of the anonymous serum specimens from the 733 non-COVID-19 individuals. The peak serum geometric mean NAb titer was significantly higher among the eight ICU patients than the 42 non-ICU patients (7280 [95% confidence interval (CI) 1468-36099]) vs (671 [95% CI, 368-1223]). Furthermore, NAb titer increased significantly at earlier infection stages among ICU patients than among non-ICU patients. The median number of days to reach the peak Nab titers after symptoms onset was shorter among the ICU patients (17.6) than that of the non-ICU patients (20.1). Multivariate analysis showed that oxygen requirement and fever during admission were the only clinical factors independently associated with higher NAb titers. Our data suggested that SARS-CoV-2 was unlikely to have silently spread before the COVID-19 emergence in Hong Kong. ICU patients had an accelerated and augmented NAb response compared to non-ICU patients, which was associated with disease severity. Further studies are required to understand the relationship between high NAb response and disease severity.