A prospective, open-label, non-randomized phase 1/2 trial reported that Sputnik Light has a good safety profile and elicits robust humoral and cellular immune responses both in seropositive and seronegative healthy adults.

Investigators undertook this study to examine the immunogenicity, safety, and tolerability of Sputnik Light vaccine, a novel single-dose vaccine based on recombinant adenovirus type 26 (rAd26) vector carrying the gene for SARS-CoV-2 spike (S) glycoprotein ” for prevention of COVID-19 infection in healthy people.

Antigen-specific humoral immunity (Anti-receptor-binding domain [RBD]-SARS-CoV-2 antibodies measured by ELISA on days 1, 10, 28, and 42) and safety (number of people with adverse events monitored throughout the trial) were the major endpoints ascertained.

Antigen-specific cellular immunity (estimated by antigen-dependent CD4+ and CD8+ T-cell proliferation, number of antigen-specific interferon-γ-producing cells, concentration pf interferon-γ upon antigen restimulation) and alteration in neutralizing antibodies (estimated in coronavirus neutralization assay) were the secondary endpoints ascertained.

The majority of the solicited noxious reactions were mild (66·4% from all vaccinees), and few were moderate (5·5%). There were no serious adverse events noted. Evaluation of Anti-RBD-SARS-CoV-2 antibodies indicated a group with pre-existing immunity to coronavirus. In view of this finding, the study researchers separated all immunogenicity and safety data on the basis of pre-existing immunity to COVID-19.

In the study groups, profound differences were witnessed in the vaccine effects on immunogenicity.

The vaccination of seropositive participants (n=14) promptly boosted RBD-specific IgGs from reciprocal geometric mean titer (GMT) 594·4 at a baseline up to 26899 in comparison with 29·09 in the seronegative participants (n=96) by day 10.

By day 42, the seroconversion rate reached 100% (93/93) in seronegative adults with GMT 1648 and 92·9% (13/14) with GMT 19986 in the seropositive adults. Evaluation of neutralizing antibodies to coronavirus depicted 81·7% (76/93) and 92·9% (13/14) seroconversion rates by day 42 with the median reciprocal GMT 15·18 and 579·7 in the seronegative and seropositive groups, respectively.

The percentage of people in seronegative group and seropositive group in which antigen-specific T cell proliferation, formation of IFNy-producing cells, and IFNy secretion were noted, is shown in Table 1:

Sputnik Light can be considered not only for primary vaccination but also could be valuable as an efficient tool for additional revaccination or vaccination following previous SARS-CoV-2 infection, concluded the study authors.