Higher Delta variant-specific neutralizing antibodies prevented infection in close contacts vaccinated with ancestral mRNA vaccines during the SARS-CoV-2 Delta wave.

Identification of the risk factors and the high-risk groups which are most vulnerable is critical in COVID-19 disease management at a population level. Evaluating the efficacy of vaccination against infections is necessary to determine booster vaccination strategies for better protection in high-risk groups. In this study, we recruited 158 mRNA-vaccinated individuals during the Delta wave of SARS-CoV-2 infections in Singapore and examined the antibody profiles of infected individuals. We found that, despite high exposure due to communal living conditions in proximity, 4% of individuals (6/158) had PCR-confirmed infections and 96% (152/158) remained uninfected. Time-course analysis of the antibody profile at the start and the end of quarantine period showed Delta-specific boosting of anti-spike antibody response in 57% of the uninfected individuals (86/152). In the remaining 43% of the uninfected individuals (66/152) with no Delta-specific antibody boost, we found a higher Delta-specific antibody response at the start of quarantine period, which correlated with higher Delta pseudovirus neutralizing capacity. Our findings indicate that a higher basal variant-specific antibody response in the mRNA-vaccinated individuals contributes to better protection against infections by the new emerging SARS-CoV-2 variants.

Clinical Course, Immunogenicity, and Efficacy of BNT162b2 mRNA Vaccination Against SARS-CoV-2 Infection in Liver Transplant Recipients.

Background: Immunocompromised individuals have been excluded from landmark studies of messenger RNA vaccinations for severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). In such patients, the response to vaccination may be blunted and may wane more quickly compared with immunocompetent patients. We studied the factors associated with decreased antibody response to SARS-CoV-2 vaccination and risk factors for subsequent breakthrough infections in liver transplant (LT) patients undergoing coronavirus disease 2019 vaccination with at least 2 doses of messenger RNA vaccine from April 28, 2021, to April 28, 2022. Methods: All LT recipients received at least 2 doses of the BNT162b2 (Pfizer BioNTech) vaccine 21 d apart. We measured the antibody response against the SARS-CoV-2 spike protein using the Roche Elecsys immunoassay to the receptor-binding domain of the SARS-CoV-2 spike protein, and the presence of neutralizing antibodies was measured by the surrogate virus neutralization test (cPass) before first and second doses of vaccination and also between 2 and 3 mo after the second dose of vaccination. Results: Ninety-three LT recipients who received 2 doses of BNT162b2 were included in the analysis. The mean time from LT was 110 ± 154 mo. After 2-dose vaccination, 38.7% of LT recipients (36/93) were vaccine nonresponders on the cPass assay compared with 20.4% (19/93) on the Roche S assay. On multivariable analysis, increased age and increased tacrolimus trough were found to be associated with poor neutralizing antibody response (P = 0.038 and 0.022, respectively). The use of antimetabolite therapy in conjunction with tacrolimus approached statistical significance (odds ratio 0.21; 95% confidence interval, 0.180-3.72; P = 0.062). Breakthrough infection occurred in 18 of 88 LT recipients (20.4%). Female gender was independently associated with breakthrough infections (P < 0.001). Conclusions: Among LT recipients, older age and higher tacrolimus trough levels were associated with poorer immune response to 2-dose SARS-CoV-2 vaccination. Further studies are needed to assess variables associated with breakthrough infections and, hence, who should be prioritized for booster vaccination.

Third dose of BNT162b2 improves immune response in liver transplant recipients to ancestral strain but not Omicron BA.1 and XBB.

Vaccine immunogenicity in transplant recipients can be impacted by the immunosuppressive (IS) regimens they receive. While BNT162b2 vaccination has been shown to induce an immune response in liver transplant recipients (LTRs), it remains unclear how different IS regimens may affect vaccine immunogenicity after a third BNT162b2 dose in LTRs, which is especially important given the emergence of the Omicron sublineages of SARS-CoV-2. A total of 95 LTRs receiving single and multiple IS regimens were recruited and offered three doses of BNT162b2 during the study period. Blood samples were collected on days 0, 90, and 180 after the first BNT162b2 dose. At each time point, levels of anti-spike antibodies, their neutralizing activity, and specific memory B and T cell responses were assessed. LTRs receiving single IS regimens showed an absence of poor immunogenicity, while LTRs receiving multiple IS regimens showed lower levels of spike-specific antibodies and immunological memory compared to vaccinated healthy controls after two doses of BNT162b2. With a third dose of BNT162b2, spike-specific humoral, memory B, and T cell responses in LTR significantly improved against the ancestral strain of SARS-CoV-2 and were comparable to those seen in healthy controls who received only two doses of BNT162b2. However, LTRs receiving multiple IS regimens still showed poor antibody responses against Omicron sublineages BA.1 and XBB. A third dose of BNT162b2 may be beneficial in boosting antibody, memory B, and T cell responses in LTRs receiving multiple IS regimens, especially against the ancestral Wuhan strain of SARS-CoV-2. However, due to the continued vulnerability of LTRs to presently circulating Omicron variants, antiviral treatments such as medications need to be considered to prevent severe COVID-19 in these individuals.

Lower vaccine-acquired immunity in the elderly population following two-dose BNT162b2 vaccination is alleviated by a third vaccine dose.

Understanding the impact of age on vaccinations is essential for the design and delivery of vaccines against SARS-CoV-2. Here, we present findings from a comprehensive analysis of multiple compartments of the memory immune response in 312 individuals vaccinated with the BNT162b2 SARS-CoV-2 mRNA vaccine. Two vaccine doses induce high antibody and T cell responses in most individuals. However, antibody recognition of the Spike protein of the Delta and Omicron variants is less efficient than that of the ancestral Wuhan strain. Age-stratified analyses identify a group of low antibody responders where individuals ≥60 years are overrepresented. Waning of the antibody and cellular responses is observed in 30% of the vaccinees after 6 months. However, age does not influence the waning of these responses. Taken together, while individuals ≥60 years old take longer to acquire vaccine-induced immunity, they develop more sustained acquired immunity at 6 months post-vaccination. A third dose strongly boosts the low antibody responses in the older individuals against the ancestral Wuhan strain, Delta and Omicron variants.

Heterologous booster vaccination with CoronaVac following prime vaccination with mRNA vaccine.

Objective: Despite the high vaccine efficacy of mRNA COVID-19 vaccines, there are individuals who developed excessive reactogenic and/or allergic responses after the first mRNA dose and were considered ineligible for further mRNA doses. CoronaVac, an inactivated SARS-CoV-2 vaccine, is recommended in Singapore as an alternative. Methods: Individuals, ineligible for further mRNA vaccines (BNT162b2 or mRNA-1273) because of excessive reactive responses to prime mRNA vaccination, were recruited and offered two doses of CoronaVac as booster vaccination 38-224 days post their mRNA vaccine dose. Individuals who did not develop any excessive reactive responses after the prime mRNA vaccination were also recruited and given another mRNA vaccine as booster vaccination. Blood samples were collected at days 0, 21 and 90 post first CoronaVac dose and mRNA dose, respectively, for analysis. Results: We showed that two CoronaVac booster doses induced specific immunity in these mRNA vaccine-primed individuals. Although the spike-specific antibody response was lower, their memory B cell response against the receptor-binding domain (RBD) of the spike protein was similar, compared with individuals who received two BNT162b2 injections. The spike-specific memory T cell response also increased following CoronaVac booster doses. However, specific immunity against the Omicron variant was low, similar to individuals with two BNT162b2 doses. Conclusion: Our findings showed that while mRNA vaccine-primed individuals can opt for two subsequent doses of CoronaVac, an additional dose may be necessary to achieve protection, especially against newly emerging immune escape variants such as Omicron.

Antibody Response of Heterologous vs Homologous Messenger RNA Vaccine Boosters Against the Severe Acute Respiratory Syndrome Coronavirus 2 Omicron Variant: Interim Results from the PRIBIVAC Study, a Randomized Clinical Trial.

BACKGROUND: Waning antibody levels post-vaccination and the emergence of variants of concern (VOCs) capable of evading protective immunity have raised the need for booster vaccinations. However, which combination of coronavirus disease 2019 (COVID-19) vaccines offers the strongest immune response against the Omicron variant is unknown. METHODS: This randomized, participant-blinded, controlled trial assessed the reactogenicity and immunogenicity of different COVID-19 vaccine booster combinations. A total of 100 BNT162b2-vaccinated individuals were enrolled and randomized 1:1 to either homologous (BNT162b2 + BNT162b2 + BNT162b2; "BBB") or heterologous messenger RNA (mRNA) (BNT162b2 + BNT162b2 + mRNA-1273; "BBM") booster vaccine. The primary end point was the level of neutralizing antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) wild-type and VOCs at day 28. RESULTS: A total of 51 participants were allocated to BBB and 49 to BBM; 50 and 48, respectively, were analyzed for safety and immunogenicity outcomes. At day 28 post-boost, mean SARS-CoV-2 spike antibody titers were lower with BBB (22 382 IU/mL; 95% confidence interval [CI], 18 210 to 27 517) vs BBM (29 751 IU/mL; 95% CI, 25 281 to 35 011; P = .034) as was the median level of neutralizing antibodies: BBB 99.0% (interquartile range [IQR], 97.9% to 99.3%) vs BBM 99.3% (IQR, 98.8% to 99.5%; P = .021). On subgroup analysis, significant higher mean spike antibody titer, median surrogate neutralizing antibody level against all VOCs, and live Omicron neutralization titer were observed only in older adults receiving BBM. Both vaccines were well tolerated. CONCLUSIONS: Heterologous mRNA-1273 booster vaccination compared with homologous BNT123b2 induced a stronger neutralizing response against the Omicron variant in older individuals. CLINICAL TRIALS REGISTRATION: NCT05142319.

Decreased memory B cell frequencies in COVID-19 delta variant vaccine breakthrough infection.

The SARS-CoV-2 Delta (B.1.617.2) variant is capable of infecting vaccinated persons. An open question remains as to whether deficiencies in specific vaccine-elicited immune responses result in susceptibility to vaccine breakthrough infection. We investigated 55 vaccine breakthrough infection cases (mostly Delta) in Singapore, comparing them against 86 vaccinated close contacts who did not contract infection. Vaccine breakthrough cases showed lower memory B cell frequencies against SARS-CoV-2 receptor-binding domain (RBD). Compared to plasma antibodies, antibodies secreted by memory B cells retained a higher fraction of neutralizing properties against the Delta variant. Inflammatory cytokines including IL-1ß and TNF were lower in vaccine breakthrough infections than primary infection of similar disease severity, underscoring the usefulness of vaccination in preventing inflammation. This report highlights the importance of memory B cells against vaccine breakthrough and suggests that lower memory B cell levels may be a correlate of risk for Delta vaccine breakthrough infection.

Virological and serological kinetics of SARS-CoV-2 Delta variant vaccine breakthrough infections: a multicentre cohort study.

OBJECTIVES: Highly effective vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been developed but variants of concerns are worrisome, especially B.1.617.2 (Delta) which has rapidly spread across the world. We aim to study if vaccination alters virological and serological kinetics in breakthrough infections. METHODS: We conducted a multicentre retrospective cohort study of patients in Singapore who had received a licensed mRNA vaccine and been admitted to hospital with B.1.617.2 SARS-CoV-2 infection. We compared clinical features, virological and serological kinetics (anti-nucleocapsid, anti-spike and surrogate virus neutralization titres) between fully vaccinated and unvaccinated individuals. RESULTS: Out of 218 individuals with B.1.617.2 infection, 84 received an mRNA vaccine of which 71 were fully vaccinated, 130 were unvaccinated and four received a non-mRNA vaccine. Despite significantly older age in the vaccine breakthrough group, only 2.8% (2/71) developed severe COVID-19 requiring oxygen supplementation compared with 53.1% (69/130) in the unvaccinated group (p < 0.001). Odds of severe COVID-19 following vaccination were significantly lower (adjusted odds ratio 0.07 95% CI 0.015-0.335, p 0.001). PCR cycle threshold values were similar between vaccinated and unvaccinated groups at diagnosis, but viral loads decreased faster in vaccinated individuals. Early, robust boosting of anti-spike protein antibodies was observed in vaccinated patients; however, these titres were significantly lower against B.1.617.2 than the wildtype vaccine strain. DISCUSSION: The mRNA vaccines are highly effective at preventing symptomatic and severe COVID-19 associated with B.1.617.2 infection. Vaccination is associated with faster decline in viral RNA load and a robust serological response. Vaccination remains a key strategy for control of the COVID-19 pandemic.

Controlled human malaria infection-Maker and breaker of dogma.

Jean-Marc Chavatte and Georges Snounou discuss research involving controlled malaria infections.

First case of Plasmodium relictum lineage pGRW11 infection in a captive-bred common eider (Somateria Mollissima) in Europe.

A 4-year-old, female common Eider (Somateria mollissima) was presented for mild lethargy with no previous medical history. Numerous intraerythrocytic, round-shaped inclusions were visualized on blood smears, later morphologically identified as Plasmodium relictum parasites. Despite oral doxycycline treatment, clinical condition declined 48 h later. Supportive care was initiated, but the bird died rapidly. Necropsy revealed acute, internal hemorrhages (lungs, air sacs) and subcutaneous, diffuse cervical hematoma, associated with resuscitation attempts. Marked, multicentric amyloidosis (kidney, liver, spleen) was the main histological finding. Molecular analysis identified lineage pGRW11 of P. relictum. This is the first reported case of P. relictum lineage pGRW11 infection in a common Eider. This report describes the clinical features, diagnosis, treatment and associated pathological findings of infection by P. relictum lineage pGRW11 in a common Eider.

The complete mitochondrial genome of Dermacentor (Indocentor) auratus (Acari, Ixodidae).

Dermacentor (Indocentor) auratus Supino, 1897 is a prominent ixodid vector of numerous pathogens of public health and veterinary importance. Using long-range PCR of two overlapping regions sequenced on an Illumina MiSeq machine, the complete mitochondrial genome of D. auratus is reported here. The resulting contigs were able to be assembled into a complete and circularised genome which had the general organisation of the mitochondrial genomes of the Metastriates. It had a total length of 14,766 bp and contained 37 genes, including 13 protein-coding genes, 22 transfer RNA genes, and 2 ribosomal RNA genes, as well as 2 non-coding control regions and 3 tick-boxes. The phylogenetic analysis on the whole mitogenome confirmed the position of D. auratus within the Dermacentor clade.

TITLE: Le génome mitochondrial complet de Dermacentor (Indocentor) auratus (Acari, Ixodidae). ABSTRACT: Dermacentor (Indocentor) auratus Supino, 1897 est un ixode, vecteur notable de nombreux pathogènes importants en santé publique et en médecine vétérinaire. Utilisant la PCR en fragment long sur deux régions chevauchantes combinée au séquençage sur une plate-forme Illumina MiSeq, le génome mitochondrial complet de D. auratus est présenté ici. Les contigs obtenus ont été assemblés en un génome circulaire complet conforme à l'organisation générale des génomes mitochondriaux des Métastriates. D'une longueur totale de 14766 pb, il contient 37 gènes, incluant 13 gènes codants des protéines, 22 gènes d'ARN de transfert et 2 gènes d'ARN ribosomaux, ainsi que 2 régions contrôles non-codantes et 3 motifs « tick-box ¼. L'analyse phylogénétique sur le mitogénome complet confirme la position de D. auratus au sein du clade Dermacentor.

Sensitive detection of total anti-Spike antibodies and isotype switching in asymptomatic and symptomatic individuals with COVID-19.

Early detection of infection is crucial to limit the spread of coronavirus disease 2019 (COVID-19). Here we develop a flow cytometry-based assay to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein antibodies in individuals with COVID-19. The assay detects specific immunoglobulin M (IgM), IgA, and IgG in individuals with COVID-19 and also acquisition of all IgG subclasses, with IgG1 being the most dominant. The antibody response is significantly higher at a later stage of infection. Furthermore, asymptomatic individuals with COVID-19 also develop specific IgM, IgA, and IgG, with IgG1 being the most dominant subclass. Although the antibody levels are lower in asymptomatic infection, the assay is highly sensitive and detects 97% of asymptomatic infections. These findings demonstrate that the assay can be used for serological analysis of symptomatic and asymptomatic infections, which may otherwise remain undetected.

Emergence of the zoonotic tick Dermacentor (Indocentor) auratus Supino, 1897 (Acari: Ixodidae) in Singapore.

Though ticks pose a significant public health risk, until recently, little research had focused on the diversity of ticks and tick-borne diseases in Singapore. To date, only fourteen tick species in five genera have been recorded there. For the first time, Dermacentor auratus is recorded from Singapore from a range of hosts, including humans. DNA sequences are provided at 2 loci, for D. auratus, the cytochrome c oxidase I (COI) for DNA barcoding and the 16S large subunit ribosomal RNA (16S lsu rRNA). The health risk posed by D. auratus in Singapore is discussed.

Neurocysticercosis Diagnosed by Taenia solium PCR on Brain Biopsy.

Neurocysticercosis is a common cause for brain lesions and adult-onset epilepsy in endemic countries. However, diagnosis is challenging in the absence of typical radiologic or histopathologic features. In this case report, we present a case of a 35-year-old male with a new-onset seizure and a rim-enhancing temporal lobe lesion. Radiologic features were nonspecific, and brain biopsy was performed. Histologic features showed only nonspecific granulomatous inflammation, and the diagnosis of neurocysticercosis was confirmed only with polymerase chain reaction (PCR) testing on brain biopsy tissue demonstrating PCR products consistent with Taenia solium. This case highlights the diagnostic role of PCR in such clinical situations whereby the diagnosis is unclear after initial routine evaluation.

Discovery and Genomic Characterization of a 382-Nucleotide Deletion in ORF7b and ORF8 during the Early Evolution of SARS-CoV-2.

To date, limited genetic changes in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) genome have been described. Here, we report a 382-nucleotide (nt) deletion in SARS-CoV-2 that truncates open reading frame 7b (ORF7b) and ORF8, removing the ORF8 transcription regulatory sequence (TRS) and eliminating ORF8 transcription. The earliest 382-nt deletion variant was detected in Singapore on 29 January 2020, with the deletion viruses circulating in the country and accounting for 23.6% (45/191) of SARS-CoV-2 samples screened in this study. SARS-CoV-2 with the same deletion has since been detected in Taiwan, and other ORF7b/8 deletions of various lengths, ranging from 62 nt to 345 nt, have been observed in other geographic locations, including Australia, Bangladesh, and Spain. Mutations or deletions in ORF8 of SARS-CoV have been associated with reduced replicative fitness and virus attenuation. In contrast, the SARS-CoV-2 382-nt deletion viruses showed significantly higher replicative fitness in vitro than the wild type, while no difference was observed in patient viral load, indicating that the deletion variant viruses retained their replicative fitness. A robust antibody response to ORF8 has been observed in SARS-CoV-2 infection, suggesting that the emergence of ORF8 deletions may be due to immune-driven selection and that further deletion variants may emerge during the sustained transmission of SARS-CoV-2 in humans.IMPORTANCE During the SARS epidemic in 2003/2004, a number of deletions were observed in ORF8 of SARS-CoV, and eventually deletion variants became predominant, leading to the hypothesis that ORF8 was an evolutionary hot spot for adaptation of SARS-CoV to humans. However, due to the successful control of the SARS epidemic, the importance of these deletions for the epidemiological fitness of SARS-CoV in humans could not be established. The emergence of multiple SARS-CoV-2 strains with ORF8 deletions, combined with evidence of a robust immune response to ORF8, suggests that the lack of ORF8 may assist with host immune evasion. In addition to providing a key insight into the evolutionary behavior of SARS-CoV-2 as the virus adapts to its new human hosts, the emergence of ORF8 deletion variants may also impact vaccination strategies.

Imported Human Babesiosis, Singapore, 2018.

In 2018, Babesia microti infection was diagnosed for a 37-year-old man in Singapore who acquired the infection in the United States. This case highlights the recent rise of tickborne infections in the United States and the risk for their spread, because of increasing global interconnectivity, to regions where they are not endemic.