Low immune response after 1.5 years of primary SARS-CoV-2 infection and Covishield vaccination lead to SARS-CoV-2 reinfection

We have investigated six COVID recovered cases with two doses of Covishield vaccination followed by reinfection. The primary SARS-CoV-2 infection found to occur with B.1 and reinfection with Omicron BA.1 and BA.2 variants. The genomic characterization and duration between two infections confirms these cases as SARS-CoV-2 reinfection. The mutation analysis of the reinfection cases correlated with immune evasion potential of BA.1 and BA.2 sub lineages. The immune response determined at different time intervals demonstrated boost post two dose vaccination, decline in pre-reinfection sera post 7 months and rise post reinfection. Apparently, these cases suffered from SARS-CoV-2 reinfection with the declined hybrid immunity acquired from primary infection and two dose covishield vaccination. This suggests the need for booster dose of vaccination. Besides this, multiple non-pharmaceutical interventions should be used to cope up with SARS-CoV-2 infection.

Persistence of immunity and impact of a third (booster) dose of an inactivated SARS-CoV-2 vaccine, BBV152; a phase 2, double-blind, randomised controlled trial

BackgroundNeutralising antibody responses to SARS-CoV-2 vaccines have been reported to decline within 6 months of vaccination, particularly against Variants of Concern (VOC). We assessed the immunogenicity and safety of a booster dose of BBV152 administered 6 months after the second of a two-dose primary vaccination series. MethodsIn an ongoing phase 2 trial (ClinicalTrials.gov: NCT04471519) the protocol was amended after six months to re-consent and randomise 184 previously vaccinated participants to receive a third dose of vaccine or placebo on Day 215. The primary outcome was to measure neutralising antibody titres by plaque-reduction neutralisation test (PRNT50) four weeks after the booster; safety as serious adverse events (SAE) was the key secondary outcome. FindingsFour weeks after a second BBV152 vaccination geometric mean titres (GMTs) of neutralising antibodies were 197{middle dot}0 PRNT50 (95% CI: 155{middle dot}6-249{middle dot}4); this level declined to 23{middle dot}9 PRNT50 (14{middle dot}0-40{middle dot}6) six months later, with a seroconversion rate of 75{middle dot}4% (95% CI: 68{middle dot}4-81{middle dot}6). Four weeks after booster vaccination the GMT increased on Day 243 to 746{middle dot}6 PRNT50 (514{middle dot}9-1081) compared with 100{middle dot}7 PRNT50 (43{middle dot}6-232{middle dot}6) in the placebo group. Corresponding seroconversion rates were 98{middle dot}7% (92{middle dot}8-99{middle dot}9) and 79{middle dot}8% (69{middle dot}6-87{middle dot}8). Increased titres in the placebo group were attributed to natural infection as the study was conducted during the second wave of COVID-19 in India. PRNT50 titres against the SARS-CoV-2 variants increased--Alpha (32{middle dot}6-fold), Beta (161{middle dot}0-fold), Delta (264{middle dot}7-fold), and Delta plus (174{middle dot}2-fold)--after the booster vaccination. We found that vaccine induces both memory B and T cells with a distinct AIM+ specific CD4+T central and effector memory phenotype, including CD8+ TEMRA phenotype. Reactogenicity after vaccine and placebo was minimal and comparable, and no SAEs were reported. InterpretationSix months after a two-dose BBV152 vaccination series cell mediated immunity and neutralising antibodies to both homologous (D614G) and heterologous strains (Alpha, Beta, Delta and Delta plus) persisted above baseline, although the magnitude of the responses had declined. Neutralising antibodies against homologous and heterologous SARS-CoV-2 variants increased 19- to 97-fold after a third vaccination. Booster BBV152 vaccination is safe and may be necessary to ensure persistent immunity to prevent breakthrough infections. FundingThis work was supported and funded by Bharat Biotech International Limited.

SARS-CoV-2 Delta derivatives impact on neutralization of Covishield recipient sera

The emergence of SARS-CoV-2 Delta variant and its derivatives has created grave public health problem worldwide. The high transmissibility associated with this variant has led to daily increase in the number of SARS-CoV-2 infections. Delta variant has slowly dominated the other variants of concern. Subsequently, Delta has further mutated to Delta AY.1 to Delta AY.126. Of these, Delta AY.1 has been reported from several countries including India and considered to be highly infectious and probable escape mutant. Considering the possible immune escape, we had already evaluated the efficacy of the BBV152 against Delta and Delta AY.1 variants. Here, we have evaluated the neutralizing potential of sera of COVID-19 naive vaccinees (CNV) immunized with two doses of vaccine, COVID-19 recovered cases immunized with two doses of vaccine (CRV) and breakthrough infections (BTI) post immunization with two doses of vaccine against Delta, Delta AY.1 and B.1.617.3 using 50% plaque reduction neutralization test (PRNT50). Our study observed low NAb titer in CNV group against all the variants compared to CRV and BTI groups. Delta variant has shown highest reduction of 27.3-fold in NAb titer among CNV group compared to other groups and variants. Anti-S1-RBD IgG immune response among all the groups was also substantiated with NAb response. Compromised neutralization was observed against Delta and Delta AY.1 compared B.1 in all three groups. However, it provided protection against severity of the disease and fatality.

Protective immunity of the primary SARS-CoV-2 infection reduces disease severity post re-infection with Delta variants in Syrian hamsters

Delta variant has evolved to become dominant SARS-CoV-2 lineage worldwide and there are reports of secondary infections with varying severity in vaccinated and unvaccinated naturally recovered COVID-19 patients. As the protective immunity following the infection wanes within few months, studies of re-infection after prolonged duration is needed. Hence we assessed the potential of re-infection by Delta, Delta AY.1 and B.1 in COVID-19 recovered hamsters after 3 months of infection. Re-infection with Delta and B.1 variants in hamsters showed reduced viral shedding, lung pathology and lung viral load, whereas the upper respiratory tract viral load remained similar to that of first infection. The reduction in viral load and lung pathology after re-infection with Delta AY.1 variant was not marked. Further we assessed the disease characteristics of Delta AY.1 to understand whether it has any replication advantage over Delta variant and B.1 variant, an early isolate in Syrian hamsters. Body weight changes, viral load in respiratory organs, lung pathology, cytokine response and neutralizing antibody response were assessed. Delta AY.1 variant produced milder disease in comparison to Delta variant and the neutralizing response was similar against Delta, B.1 and B.1.351 variant in contrast to Delta or B.1 infected hamsters which showed a significant reduction in neutralization titres against B.1.351. Elevation of IL-6 levels was observed post infection in hamsters after primary infection. The prior infection could not produce sterilizing immunity but the protective effect was evident following reinfection. This indicates the importance of the transmission prevention efforts even after achieving herd immunity. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSSecondary infections with Delta variant are being widely reported and there are reports of increased disease severity. Delta sub lineages with K417N substitution has caused concern worldwide due to the presence of the same substitution in Beta variant, a Variant of Concern known for its immune evasion. The information on the biological characteristics of this sub lineage is also scanty. Added value of this studyThe present study showed that the secondary infection with Delta variant does not show any evidence of increased disease severity in hamster model. Delta AY. 1 variant produces mild disease in Syrian hamsters in contrast to severe disease caused by Delta variant. Delta, B.1 and AY.1 variant infected hamster sera showed comparable cross neutralizing response against each other. In contrast to the lower neutralizing response shown by B.1 and Delta variant infected animals against B.1.351 variant, Delta AY.1 showed comparable response as that with other variants. Implications of the available evidenceSARS-CoV-2 infections do not produce sterilizing immunity but protect from developing severe disease in case of Delta variant re-infection indicating the importance of the transmission prevention efforts even after achieving herd immunity. Delta AY. 1 infection in hamsters did not show any evidence of speculated immune evasion.

SARS-CoV-2 Delta variant pathogenesis and host response in Syrian hamsters

B.1.617 lineage is becoming a dominant SARS-CoV-2 lineage worldwide and was the dominant lineage reported in second COVID-19 wave in India, which necessitated studying the properties of the variant. We evaluated the pathogenicity and virus shedding of B.1.617.2 (Delta) and B.1.617.3 lineage of SARS-CoV-2 and compared with that of B.1, an early virus isolate with D614G mutation in Syrian hamster model. Viral load, antibody response and lung disease were studied. No significant difference in the virus shedding pattern was observed among these variants studied. A significantly high SARS-CoV-2 sub genomic RNA could be detected in the respiratory tract of hamsters infected with Delta variant for 14 days. Delta variant induced lung disease of moderate severity in 40% of infected animals. The neutralizing capability of the B.1, Delta and B.1.617.3 variant infected animals were found significantly lower with the B.1.351 (Beta variant). The findings of the study support the attributed disease severity and the increased transmission potential of the Delta variant.

Neutralization potential of Covishield vaccinated individuals against B.1.617.1

Covishield comprises the larger proportion in the vaccination program in India. Hence, it is of utmost importance to understand neutralizing capability of vaccine against the B.1.617.1 variant which is considered to responsible for surge of the cases in India. The neutralizing-antibody (NAb) titer against B.1.167.1 and prototype B.1 variant (D614G) was determined of the vaccine sera (4 weeks after second dose) of COVID-19 naive subjects (n=43) and COVID-19 recovered subjects (n=18). The results demonstrated that sera of COVID-19 recovered subjects (n=18) who received two doses of Covishield have higher NAb response compared to the COVID-19 naive with a significant difference (p<0.0001) in NAb titer against B.1 and B.1.617.1 In-spite of reduction in the neutralizing titer against B.1.617.1 variant; Covishield vaccine-induced antibodies are likely to be protective to limit the severity and mortality of the disease in the vaccinated individuals.

SARS CoV-2 variant B.1.617.1 is highly pathogenic in hamsters than B.1 variant

BackgroundThe recent emergence of new SARS-CoV-2 lineage B.1.617 in India has been associated with a surge in the number of daily infections. This variant has combination of specific mutations L452R, E484Q and P681R reported to possibly enhance the transmissibility with likelihood of escaping the immunity. We investigated the viral load and pathogenic potential of B.1.617.1 in Syrian golden hamsters. MethodsTwo groups of Syrian golden hamsters (9 each) were inoculated intranasally with SARS CoV-2 isolates, B.1 (D614G) and B.1.617.1 respectively. The animals were monitored daily for the clinical signs and body weight. The necropsy of three hamsters each was performed on 3, 5- and 7-days post-infection (DPI). Throat swab (TS), nasal wash (NW) and organ samples (lungs, nasal turbinate, trachea) were collected and screened using SARS-CoV-2 specific Real-time RT-PCR. ResultsThe hamsters infected with B.1.617.1 demonstrated increased body weight loss compared to B.1 variant. The highest viral load was observed in nasal turbinate and lung specimens of animals infected with B.1.167.1 on 3 DPI. Neutralizing antibody (NAb) and IgG response in hamsters of both the groups were observed from 5 and 7 DPI respectively. However, higher neutralizing antibody titers were observed against B.1.167.1. Gross pathology showed pronounced lung lesions and hemorrhage with B.1.671 compared to B.1. ConclusionsB.1617.1 and B.1 variant varied greatly in their infectiousness, pathogenesis in hamster model. This study demonstrates higher pathogenicity in hamsters evident with reduced body weight, higher viral load in lungs and pronounced lung lesions as compared to B.1 variant. SummaryB.1.617.1 is the new SARS-CoV-2 lineage that emerged in India. Maximal body weight loss and higher viral load in hamsters infected with B.1.617.1. It caused pronounced lung lesions in hamsters compared to B.1 variant which demonstrates the pathogenic potential of B.1.617.1.

Neutralization of variant under investigation B.1.617 with sera of BBV152 vaccinees

The drastic rise in the number of cases in Maharashtra, India has created a matter of concern for public health experts. Twelve isolates of VUI lineage B.1.617 were propagated in VeroCCL81 cells and characterized. Convalescent sera of the COVID-19 cases and recipients of BBV152 (Covaxin) were able to neutralize VUI B.1.617.

Neutralization of UK-variant VUI-202012/01 with COVAXIN vaccinated human serum

We performed the plaque reduction neutralization test (PRNT50) using sera collected from the 26 recipients of BBV152/COVAXIN against hCoV-19/India/20203522 (UK-variant) and hCoV27 19/India/2020Q111 (heterologous strain). A comparable neutralization activity of the vaccinated individuals sera showed against UK-variant and the heterologous strain with similar efficiency, dispel the uncertainty of possible neutralization escape.

Evaluation of Safety and Immunogenicity of an Adjuvanted, TH-1 Skewed, Whole Virion Inactivated SARS-CoV-2 Vaccine - BBV152

We report the development and evaluation of safety and immunogenicity of a whole virion inactivated SARS-COV-2 vaccine (BBV152), adjuvanted with aluminium hydroxide gel (Algel), or a novel TLR7/8 agonist adsorbed Algel. We used a well-characterized SARS-CoV-2 strain and an established vero cell platform to produce large-scale GMP grade highly purified inactivated antigen, BBV152. Product development and manufacturing were carried out in a BSL-3 facility. Immunogenicity was determined at two antigen concentrations (3g and 6g), with two different adjuvants, in mice, rats, and rabbits. Our results show that BBV152 vaccine formulations generated significantly high antigen-binding and neutralizing antibody titers, at both concentrations, in all three species with excellent safety profiles. The inactivated vaccine formulation containing TLR7/8 agonist adjuvant-induced Th1 biased antibody responses with elevated IgG2a/IgG1 ratio and increased levels of SARS-CoV-2 specific IFN-{gamma}+ CD4 T lymphocyte response. Our results support further development for Phase I/II clinical trials in humans.