Immunogenicity and protective efficacy of inactivated SARS-CoV-2 vaccine candidate, BBV152 in rhesus macaques

Abstract

The COVID-19 pandemic is a global health crisis that poses a great challenge to the public health system of affected countries. Safe and effective vaccines are needed to overcome this crisis. Here, we develop and assess the protective efficacy and immunogenicity of an inactivated SARS-CoV-2 vaccine in rhesus macaques. Twenty macaques were divided into four groups of five animals each. One group was administered a placebo, while three groups were immunized with three different vaccine candidates of BBV152 at 0 and 14 days. All the macaques were challenged with SARS-CoV-2 fourteen days after the second dose. The protective response was observed with increasing SARS-CoV-2 specific IgG and neutralizing antibody titers from 3^rd-week post-immunization. Viral clearance was observed from bronchoalveolar lavage fluid, nasal swab, throat swab and lung tissues at 7 days post-infection in the vaccinated groups. No evidence of pneumonia was observed by histopathological examination in vaccinated groups, unlike the placebo group which exhibited interstitial pneumonia and localization of viral antigen in the alveolar epithelium and macrophages by immunohistochemistry. This vaccine candidate BBV152 has completed Phase I/II (NCT04471519) clinical trials in India and is presently in phase III, data of this study substantiates the immunogenicity and protective efficacy of the vaccine candidates.

Fig. 1. Experimental summary and IgG response in vaccinated animals.

a Diagrammatic representation of experiment summary. b Anti-SARS-CoV-2 IgG response in animals from 1st to 4th week of immunisation with whole virus-inactivated protein ELISA. c Anti-SARS-CoV-2 IgG response at 0, 1, 3, 5 and 7 DPI. d Anti-SARS-CoV-2 IgG titres in animals at 0 and 7 DPI. e IgG titres for SARS-CoV-2 RBD protein in animals at 0 and 7 DPI. f IgG titres for SARS-CoV-2 nucleoprotein in animals at 0 and 7 DPI. The statistical significance was assessed using the Kruskal–Wallis test followed by the two-tailed Mann–Whitney test between two groups; P values of < 0.05 were considered to be statistically significant. The dotted line on the figures indicates the limit of detection of the assay. Data are presented as mean values +/− standard deviation (SD). Statistical comparison was done by comparing the vaccinated group with the placebo group as a control. Group I = blue, group II = pink, group III = green and group IV = purple, number of animals = 5 animals in each group. Source data are provided as a Source Data file.

Fig. 2. NAb response in vaccinated animals.

a NAb titres in animals from 1st to 4th week of immunisation. b NAb titres in animals at 0, 1, 3, 5 and 7 DPI. c NAb titres in animal samples of 7 DPI with homologous strain 770 and heterologous strain Q-100 and Q-111 of SARS-CoV-2. The statistical significance was assessed using the Kruskal–Wallis test followed by the two-tailed Mann–Whitney test between two groups; P values of < 0.05 were considered to be statistically significant. Data are presented as mean values +/− standard deviation (SD). Statistical comparison was done by comparing the vaccinated group with the placebo group as a control. Group I = blue, group II = pink, group III = green and group IV = purple, number of animals = 5 animals in each group. Source data are provided as a Source Data file.

Fig. 3. Genomic viral RNA detection in respiratory tract specimens.

Genomic viral RNA load in (a) nasal swab, (b) throat swab and (c) BAL at 1, 3, 5 and 7 DPI. d Genomic viral RNA load in different lobes of lungs at 7 DPI. The statistical significance was assessed using the Kruskal–Wallis test followed by the two-tailed Mann–Whitney test between the two groups; P values < 0.05 were considered to be statistically significant. The dotted lines indicate the limit of detection of the assay. Data are presented as mean values +/− standard deviation (SD). Statistical comparison was done by comparing the vaccinated group with the placebo group as a control. Group I = blue, group II = pink, group III = green and group IV = purple, number of animals = 5 animals in each group. Source data are provided as a Source Data file.

Fig. 4. Subgenomic viral RNA detection in the respiratory tract specimens.

sgRNA load in (a) BAL at 7 DPI, (b) sgRNA in different lobes of lungs at 7 DPI, (c) throat swab at 1 DPI and (d) sgRNA load in NS at 1, 3, 5 and 7 DPI. The statistical significance was assessed using the Kruskal–Wallis test followed by the two-tailed Mann–Whitney test between the two groups; P values < 0.05 were considered to be statistically significant. The dotted lines indicate the limit of detection of the assay. Data are presented as mean values +/− standard deviation (SD). Statistical comparison was done by comparing the vaccinated group with the placebo group as a control. Group I = blue, group II = pink, group III = green and group IV = purple, number of animals = 5 animals in each group. Source data are provided as a Source Data file.

Fig. 5. Gross pathology of lungs and viral RNA load in different tissues.

a Lungs showing extensive involvement of the right upper lobe (RUL), right lower lobe (RLL), left upper lobe (LUL) and left lower lobe (LLL) (group I) and (b) normal lung (group III) (c) genomic viral RNA of respiratory tract tissues (d), lungs tissue and (e) extrapulmonary organs at 7 DPI. The dotted lines indicate the limit of detection of the assay. Group I = blue, group II = pink, group III = green and group IV = purple, number of animals = 5 animals in each group. Source data are provided as a Source Data file.

Fig. 6. Histopathological and immunohistochemical findings.

a Lungs showing moderate acute inflammatory changes with haemorrhages and infiltration of inflammatory cells. Alveolar septa showed hyaline membrane formation (asterisks) with inflammatory cells and RBCs. The adjacent alveolar interstitium is thickened by oedema (black arrow) and moderate infiltration of lymphocytes, neutrophils and macrophages (white broad arrow). Haematoxylin and eosin-stained (H&E), ×400 magnification. b Lungs showing normal histomorphological features of alveolar septa with type I pneumocyte (white arrow) and occasional alveolar macrophages (black arrow) along the alveolar lumen in group II H&E, ×400 magnification. c Lung section depicting normal histomorphological features of alveolar septa with type I pneumocyte (white arrow) and occasional alveolar macrophages (black arrow) along the alveolar lumen in group III H&E, ×400 magnification. d Lung section depicting normal histomorphological features of alveolar septa with type I pneumocyte (white arrow) and occasional alveolar macrophages (black arrow) along the alveolar lumen in group IV H&E, ×400 magnifications. e Lungs section of placebo group showing the presence of viral antigen by immunohistochemistry (IHC) in type-I pneumocytes (arrow) of alveolar septa and in alveolar macrophages (arrow) (×400 magnification). Lung section of group II (f), group III (g) and group IV (h) showing the absence of viral antigen by IHC. Sixty sections of lung lobe are evaluated for five animals each from groups I, II, III and IV; a representative lesion from each group was selected for the figure.