Sub-optimal Neutralisation of Omicron (B.1.1.529) Variant by Antibodies induced by Vaccine alone or SARS-CoV-2 Infection plus Vaccine (Hybrid Immunity) post 6-months

Background: Rapid expansion of the omicron SARS-CoV-2 variant of concern despite extensive vaccine coverage might be related to decreased neutralising ability of vaccine induced antibodies. The neutralising ability of different vaccines with or without natural SARS-CoV-2 infection against omicron is however not well known. Methods: We tested the ability of vaccine and natural infection induced antibodies to neutralise omicron variant in a live virus neutralisation assay. Four groups of individuals were included: (i) complete vaccination with ChAdOx1 nCoV-19 (n=20), (ii) complete vaccination with ChAdOx1 nCoV-19 plus prior SARS-CoV-2 infection during the delta variant driven surge (n=20), (iii) complete vaccination with inactivated whole virus vaccine (BBV152) (n=20), (iv) complete vaccination with BBV152 plus prior SARS-CoV-2 infection (n=20). Primary outcome was fold-change in the virus neutralisation ability of plasma against the omicron variant compared with ancestral and delta variant. Findings: The neutralisation geometric mean titre (GMT) was 384 (95% CI: 662, 223) against the ancestral virus with BBV152 vaccination alone and 383 (95% CI: 709, 207) with ChAdOx1 nCov-19 vaccination alone. The corresponding values for hybrid immunity groups were 795 (95% CI: 1302, 486) and 1424 (95% CI: 2581,786) respectively. Against the omicron variant, only 5 out of 20 in both BBV152 and ChAdOx1 nCoV-19 vaccine only groups, 5 out of 19 in BBV152 plus SARS-CoV-2 infection group, and 9 out of 20 in ChAdOx1 nCoV-19 plus SARS-CoV-2 infection group exhibited neutralisation titres above the lower limit of quantification (1:20). The 50% neutralization titre against ancestral strain and omicron demonstrated strong correlation with anti-RBD IgG levels [Pearson r: 0.94 (0.91, 0.96) p: <0.001 and 0.92 (0.88, 0.95) p:<0.001 respectively]. Interpretation: Omicron variant shows significant reduction in neutralising ability of both vaccine induced and hybrid immunity induced antibodies which might explain immune escape and high transmission even in the presence of widespread vaccine coverage.

ChAdOx1 nCoV-19 (AZD1222) vaccine elicits monoclonal antibodies with potent cross-neutralizing activity against SARS-CoV-2 viral variants

Although the antibody response to COVID-19 vaccination has been studied extensively at the polyclonal level using immune sera, little has been reported on the antibody response at the monoclonal level. Here we isolate a panel of 44 anti-SARS-CoV-2 monoclonal antibodies (mAbs) from an individual who received two doses of the ChAdOx1 nCoV-19 (AZD1222) vaccine at a 12-week interval. We show that despite a relatively low serum neutralization titre, mAbs with potent neutralizing activity against the current SARS-CoV-2 variants of concern (B.1.1.7, P.1, B.1.351 and B.1.617.2) were obtained. The vaccine elicited neutralizing mAbs form 8 distinct competition groups and bind epitopes overlapping with neutralizing mAbs elicited following SARS-CoV-2 infection. AZD1222 elicited mAbs are more mutated than mAbs isolated from convalescent donors 1-2 months post infection. Spike reactive IgG+ B cells were still detectable 9-months post boost. These findings give molecular insights into AZD1222 elicited antibody response.

COVID-19 mRNA vaccine induced antibody responses against three SARS-CoV-2 variants

As SARS-CoV-2 has been circulating for over a year, dozens of vaccine candidates are under development or in clinical use. The BNT162b2 mRNA COVID-19 vaccine induces spike protein-specific neutralizing antibodies associated with protective immunity. The emergence of the B.1.1.7 and B.1.351 variants has raised concerns of reduced vaccine efficacy and increased re-infection rates. Here we show, that after the second dose, the sera of BNT162b2-vaccinated health care workers (n = 180) effectively neutralize the SARS-CoV-2 variant with the D614G substitution and the B.1.1.7 variant, whereas the neutralization of the B.1.351 variant is five-fold reduced. Despite the reduction, 92% of the seronegative vaccinees have a neutralization titre of >20 for the B.1.351 variant indicating some protection. The vaccinees’ neutralization titres exceeded those of recovered non-hospitalized COVID-19 patients. Our work provides evidence that the second dose of the BNT162b2 vaccine induces cross-neutralization of at least some of the circulating SARS-CoV-2 variants.

COVID-19 mRNA vaccine induced antibody responses and neutralizing antibodies against three SARS-CoV-2 variants

As SARS-CoV-2 has been circulating for over a year, dozens of vaccine candidates are under development or in clinical use. The BNT162b2 mRNA COVID-19 vaccine induces spike protein-specific neutralizing antibodies associated with protective immunity. The emergence of the B.1.1.7 and B.1.351 variants has raised concerns of reduced vaccine efficacy and increased re-infection rates. Here we show, that after the second dose, the sera of BNT162b2-vaccinated health care workers (n = 180) effectively neutralize the SARS-CoV-2 variant with the D614G substitution and the B.1.1.7 variant, whereas the neutralization of the B.1.351 variant is five-fold reduced. Despite the reduction, 92% of the vaccinees have a neutralization titre of >20 for the B.1.351 variant indicating some protection. The vaccinees’ neutralization titres exceeded those of recovered non-hospitalized COVID-19 patients. Our work provides strong evidence that the second dose of the BNT162b2 vaccine induces efficient cross-neutralization of SARS-CoV-2 variants currently circulating in the world.

Glycoprotein N subtypes of human cytomegalovirus induce a strain-specific antibody response during natural infection

Human cytomegalovirus (HCMV) encodes several highly polymorphic envelope glycoproteins; however, the biological relevance of this polymorphism is unclear. Glycoprotein N (gN) is one member of this polymorphic protein family. Four major gN genotypes (gN1–4) have been identified. We have tested the hypothesis that the gN polymorphism represents a mechanism to evade a neutralizing antiviral antibody response. Four recombinant viruses that differed only in the expression of the gN genotype were constructed on the genetic background of HCMV strain AD169. Exchange of gN genotypes had a minor detectable influence on virus replication, gN expression and gN–gM complex formation. Randomly selected human sera were analysed for neutralizing activity against the recombinant viruses. Of these, 70 % showed no difference in neutralizing titre between the viruses, whereas 30 % showed strain-specific neutralization. Differences in 50 % neutralization titre reached >8-fold. Viruses expressing the gN4 genotype were neutralized significantly better than those expressing the other gN genotypes. Strain specificity, or lack thereof, could not be attributed to the presence or absence of anti-gN antibodies, as all sera contained antibodies reacting with gN (as determined by ELISA). Thus, polymorphism of gN could contribute to evasion of an efficient neutralizing-antibody response and facilitate reinfection in previously seropositive individuals.

Antibody capture radioimmunoassay (MACRIA) for coxsackievirus B4 and B5-specific IgM

SUMMARYAn antibody capture radioimmunoassay was established for the detection of coxsackievirus B4 and B5-specific IgM. A significant feature of the assay was the use of an unrefined coxsackievirus B (CBV) antigen. The antigen was prepared by freeze thawing, ultrasonication and low speed centrifugation of infected Vero cells with no purification or concentration of the antigen being performed. Results of sera tested were expressed as a serum ratio (SR) by comparison with a low positive control serum. To establish an SR indicating positivity in the assays, 100 antenatal sera collected in late February were tested. The mean SR was calculated and the mean plus three standard deviations was taken as the minimum SR indicating positivity. Although resulting in a relatively insensitive assay, such a value was required to exclude sera giving a low level of reactivity which may be due to residual enterovirus-specific IgM resulting from a remote infection.The homologous CBV-IgM assay was positive in four cases of CBV4 infection and six cases of CBV5 infection. For the CBV4 IgM assay, ten of 20 (50%) sera from infections with CBV other than CBV4 were positive and nine of the 13(69%) sera from infections with echoviruses or coxsackieviruses A were positive. Five of 18 (27%) sera with an elevated CBV neutralization titre were positive in the CBV4-IgM assay. For the CB5-IgM assay seven of 18(39%) sera from infections with CBV other than CBV5 were positive and nine of 13 (69%) sera from infections with echoviruses or coxsackieviruses A were positive. The nine sera that were positive from this group in the CBV5-IgM assay were the same nine as were positive in the CBV4-IgM assay. Two of the 18(11%) sera with an elevated CBV neutralization titre were positive in the CBV5-IgM assay. These two sera were also positive in the CBV4-IgM assay and had an elevated monotypic CBV4 neutralization titre. None of the sera giving positive results gave significant reactivity when tested with control antigen. Twelve rheumatoid factor containing sera and 46 sera from other infections were negative in both assays. Of 24 sera from confirmed CBV infection, seven gave a positive monotypic CBV4 or 5-IgM response, ten were positive in both assays and seven were negative in both assays. The positive results seen with sera from cases of heterologous enterovirus infection may result from an anamnestic IgM response or, more likely, IgM directed against enterovirus cross-reacting antigens. The absence of homologous neutralizing antibody at a dilution of 1:20 in nine of 20 sera that gave a positive CBV-IgM result and the presence of positive results for CBV4 and 5-IgM in a 14 month old infant who had echovirus 7 infection indicates that the IgM need not be directed against neutralizing antigens.Thus the CBV4 and 5-IgM assays developed appeared to be specific for an enterovirus infection but because of the cross-reactivity were not type-specific or group-specific.