Long-Term Immunogenicity and Safety of a Homologous Third Dose Booster Vaccination with TURKOVAC: Phase 2 Clinical Study Findings with 32-Week Post-Booster Follow-Up

Vaccine-induced immunity wanes over time and warrants booster doses. We investigated the long-term (32 weeks) immunogenicity and safety of a third, homologous, open-label booster dose of TURKOVAC, administered 12 weeks after completion of the primary series in a randomized, controlled, double-blind, phase 2 study. Forty-two participants included in the analysis were evaluated for neutralizing antibodies (NAbs) (with microneutralization (MNT50) and focus reduction (FRNT50) tests), SARS-CoV-2 S1 RBD (Spike S1 Receptor Binding Domain), and whole SARS-CoV-2 (with ELISA) IgGs on the day of booster injection and at weeks 1, 2, 4, 8, 16, 24, and 32 thereafter. Antibody titers increased significantly from week 1 and remained higher than the pre-booster titers until at least week 4 (week 8 for whole SARS-CoV-2) (p 50: 6-fold; FRNT50: 5.4-fold) for NAbs and 32 weeks for S1 RBD (7.9-fold) and whole SARS-CoV-2 (9.4-fold) IgGs. Nine participants (20.9%) tested positive for SARS-CoV-2 RT-PCR between weeks 8 and 32 of booster vaccination; none of them were hospitalized or died. These findings suggest that boosting with TURKOVAC can provide effective protection against COVID-19 for at least 8 weeks and reduce the severity of the disease

Safety and immunogenicity of an inactivated whole virion SARS-CoV-2 vaccine, TURKOVAC, in healthy adults: Interim results from randomised, double-blind, placebo-controlled phase 1 and 2 trials.

BACKGROUND: Development of safe and effective vaccine options is crucial to the success of fight against COVID-19 pandemic. Herein, we report interim safety and immunogenicity findings of the phase 1&2 trials of ERUCoV-VAC, an inactivated whole virion SARS-CoV-2 vaccine. METHODS: Double-blind, randomised, single centre, phase 1 and 2 trials included SARS-CoV-2 seronegative healthy adults aged 18–55 years (18–64 in phase 2). All participants, except the first 4 in phase 1 who received ERUCoV-VAC 3 μg or 6 μg unblinded and monitored for 7 days for safety purposes, were assigned to receive two intramuscular doses of ERUCoV-VAC 3 μg or 6 μg (an inactivated vaccine containing alhydrogel as adjuvant) or placebo 21 days apart (28 days in phase 2) according to computer-generated randomisation schemes. Both trials are registered at ClinicalTrials.gov (phase 1, NCT04691947 and phase 2, NCT04824391). RESULTS: Forty-four participants (3 μg [n:17], 6 μg [n:17], placebo [n:10]) in phase 1 and 250 (3 μg [n:100], 6 μg [n:100], placebo [n:50]) in phase 2 received ≥1 dose. In phase 1 trial, 25 adverse events AEs (80 % mild) occured in 15 participants (34.1 %) until day 43. There was no dose-response relationship noted in safety events in ERUCoV-VAC recipients (p = 0.4905). Pain at injection site was the most common AE (9/44;20.5 %). Both doses of ERUCoV-VAC 3 μg and 6 μg groups were comparable in inducing SARS-CoV-2 wild-type neutralising antibody (MNT50): GMTs (95 %CI) were 8.3 (6.4–10.3) vs. 8.6 (7.0–10.2) at day 43 (p = 0.7357) and 9.7 (6.0–13.4) vs. 10.8 (8.8–12.8) at day 60 (p = 0.8644), respectively. FRNT50 confirmed MNT50 results: SARS-CoV-2 wild-type neutralising antibody GMTs (95 %CI) were 8.4 (6.3–10.5) vs. 9.0 (7.2–10.8) at day 43 (p = 0.5393) and 11.0 (7.0–14.9) vs. 12.3 (10.3–14.5) at day 60 (p = 0.8578). Neutralising antibody seroconversion rates (95 %CI) were 86.7 % (59.5–98.3) vs 94.1 % (71.3–99.8) at day 43 (p = 0.8727) and 92.8 % (66.1–99.8) vs. 100 % (79.4–100.0) at day 60 (p = 0.8873), in ERUCoV-VAC 3 μg and 6 μg groups, respectively. In phase 2 trial, 268 AEs, (67.2 % moderate in severity) occured in 153 (61.2 %) participants. The most common local and systemic AEs were pain at injection site (23 events in 21 [8.4 %] subjects) and headache (56 events in 47 [18.8 %] subjects), respectively. Pain at injection site was the only AE with a significantly higher frequency in the ERUCoV-VAC groups than in the placebo arm in the phase 2 study (p = 0.0322). ERUCoV-VAC groups were comparable in frequency of AEs (p = 0.4587). ERUCoV-VAC 3 μg and 6 μg groups were comparable neutralising antibody (MNT(50)): GMTs (95 %CI) were 30.0 (37.9–22.0) vs. 34.9 (47.6–22.1) at day 43 (p = 0.0666) and 34.2 (23.8–44.5) and 39.6 (22.7–58.0) at day 60, (p = 0.2166), respectively. FRNT50 confirmed MNT50 results: SARS-CoV-2 wildtype neutralising antibody GMTs were 28.9 (20.0–37.7) and 30.1 (18.5–41.6) at day 43 (p = 0.3366) and 34.2 (23.8–44.5) and 39.6 (22.7–58.0) at day 60 (p = 0.8777). Neutralising antibody seroconversion rates (95 %CI) were 95.7 % (91.4–99.8) vs. 98.9 % (96.9–100.0) at day 43 (p = 0.8710) and 96.6 % (92.8–100.0) vs 98.9 % (96.7–100.0) at day 60 (p = 0.9129) in ERUCoV-VAC 3 μg and 6 μg groups, respectively. CONCLUSIONS: Two-dose regimens of ERUCoV-VAC 3 μg and 6 μg 28 days both had an acceptable safety and tolerability profile and elicited comparable neutralising antibody responses and seroconversion rates exceeding 95 % at day 43 and 60 after the first vaccination. Data availability Data will be made available on request