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Objectives: To evaluate the immunogenicity of an extended interval regimen of BNT162b2 among healthy school-age children. Methods: A randomized-control trial conducted among healthy Thai children aged 5-11 years. Participants received two doses of BNT162b2 with an 8-week (extended dosing) vs 3-week interval. Immunogenicity was determined by neutralization test (NT) against the Omicron variant, surrogate virus NT (sVNT; BA.1, % inhibition), and pseudovirus NT (BA.2, the half-maximal inhibition dilution or ID50). The third dose was offered to participants who had sVNT

Objective: To compare the immune response of hybrid immunity – arising from SARS-CoV-2 infection and mRNA BNT162b2 vaccination – to that of 2-doses of vaccine. Methods: In a subanalysis of BNT162b2 vaccine trial in 5 to 11-year-old children, There were 179 children who had hybrid immunity compared with 134 children with solely 2-dose vaccine. The immunological outcome was a surrogate virus neutralization test (sVNT) against the Omicron strain, BA.1, (%inhibition). An sVNT level ≥68 % inhibition was considered as protective immune response. Results: From February to April 2022, 179 children had COVID-19 natural infection resulting in hybrid immunity included: Group1;prior vaccination(n = 17), Group2;after the first dose(n = 61), and Group3;after the second dose(n = 97). The proportion of children with protective immune response was higher in Group 3 and Group 1 – 61.9 % and 58.8 %, compared to 36.1 % and 34.3 % in Group 2 and comparator group (2 doses of vaccine), respectively. The geometric mean % inhibition of sVNT was higher in Group 1 (68.5, 95 %CI 55.5–84.6) and Group 3 (63.5, 95 %CI 55.5–72.6), followed by comparator group (49.6, 95 %CI 44.8–54.9) and Group 2 (42.1, 95 %CI 34.6–51.3), p

Background: Children 6 months to 6 months(N = 40) prior to vaccination. Participants in Group A and B received 2-dose BNT162b2 intramuscularly 1 month apart. COVID-naïve children were enrolled as a control group (N = 40) and received 3-dose BNT162b2 at month 0,1,3. Neutralizing antibody against Omicron variant(BA.2.75 and BA.4/5) was determined by pseudovirus assays(pVNT) as reported by neutralization dilution for 50%inhibition (ID50) at 28 days after the 1st and 2nd dose. Results: From October-November 2022, 120 children with a median age of 2.8 years (IQR 1.6–4.0) were enrolled. The median duration since COVID-19 to vaccination was 4.4 months(IQR 3.8–5.4) in Group A and 7.9 months(7.0–8.5) in Group B. In Group A, the geometric means(GMs) of pVNT-BA.2.75 ID50 were 553 (95%CI 338–906) and 753(516–1098) after 1 and 2 doses, respectively, and the GMs of pVNT-BA.4/5 ID50 were 1936(1402–2673) and 1885(1414–2512), respectively. In Group B, the GMs of pVNT-BA.2.75 ID50 were 1383(1100–1742) and 1419 (1104–1823), and the GMs of pVNT-BA.4/5 ID50 were 2627(2048–3367) and 2056(1546–2735), respectively. Meanwhile in COVID-naïve group, the GMs of pVNT-BA.2.75 and pVNT-BA.4/5 ID50 were 158(98–255) and 59(31–114) after the 3rd dose, respectively. The geometric mean ratio(GMR) of pVNT-BA.2.75 ID50 after 1 dose in Group A and B compared with after 3 doses in COVID-naïve group were 3.50 (1.93–6.34) and 8.74 (4.79–15.95), respectively. The GMR of pVNT-BA.2.75 ID50 after 1 dose in Group B compared with Group A was 2.50 (1.45–4.31). Conclusions: Children previously infected with SARS-CoV-2 Omicron variant, developed robust neutralizing antibody response against Omicron variant after single-dose BNT162b2. Children with an interval of > 6 months since COVID-19 infection developed higher neutralizing antibody response compared to those with a 3-to-6-month interval.

The emergence of Omicron as the fifth variant of concern within the SARS-CoV-2 pandemic in late 2021, characterized by its rapid transmission and distinct spike gene mutations, underscored the pressing need for cost-effective and efficient methods to detect viral variants, especially given their evolving nature. This study sought to address this need by assessing the effectiveness of two SARS-CoV-2 variant classification platforms based on RT-PCR and mass spectrometry. The primary aim was to differentiate between Delta, Omicron BA.1, and Omicron BA.2 variants using 618 COVID-19-positive samples collected from Bangkok patients between November 2011 and March 2022. The analysis revealed that both BA.1 and BA.2 variants exhibited significantly higher transmission rates, up to 2-3 times, when compared to the Delta variant. This research presents a cost-efficient approach to virus surveillance, enabling a quantitative evaluation of variant-specific public health implications, crucial for informing and adapting public health strategies.

Objectives: The World Health Organization recommends a 2-dose rabies pre-exposure prophylaxis (PrEP) regimen. This study aimed to compare the immunogenicity of rabies PrEP regimens co-administered with inactivated quadrivalent influenza vaccine (IIV4). Methods: Children aged 3 to 9 years were randomly assigned (2:2:1) to receive 0.25 mL of chromatographically purified Vero cell rabies vaccine intramuscularly: Group A at day 0, 7 with IIV4; Group B at day 0, 28 with IIV4; Group C at day 0, 7. A booster-dose of CPRV was given on day 365. Primary outcome was the proportion of children with protective rabies virus neutralizing antibody (RVNA) ≥ 0.5 IU/mL, on day 42 and 7 days post-booster. Results: From November 2019 to January 2020; 100 children with a median age (IQR) of 5.4 years (4.8-7.3) were enrolled. All participants achieved protective RVNA titers on day 42 and 7-days post booster. Geometric mean titers (GMT) at day 42 were Group A, 8.98(95%CI 7.06-11.42); Group B, 23.89(95%CI 19.33-29.51); Group C, 9.94(95%CI 7.03-14.06). Likewise, RVNA GMT at 7 days post-booster were Group A, 42.53(95%CI 18.41-66.64); Group B, 23.19(95%CI 17.28-29.10); Group C, 57.75 (95%CI 35.86-79.67). Conclusions: The 2-dose PrEP regimen of rabies vaccine produces adequate immune response either 0,7 or 0, 28 regimens.

Background: A primary series of 2-dose SARS-CoV-2 vaccines based on an ancestral strain generate inadequate neutralizing antibodies against the SARS-CoV-2 Omicron variant. This study aimed to describe the immune response from giving healthy school-aged children who previously received 2 inactivated vaccines an mRNA BNT162b2 booster. Methods: Healthy children aged 5–11 years who received 2 doses of CoronaVac or Covilo were enrolled and received 10 µg BNT162b2 intramuscularly. Neutralizing antibody against Omicron variant was measured at pre-booster and 14–21 days post-booster by surrogate virus neutralization test (sVNT, %inhibition) and pseudovirus neutralization test (pVNT, ID50). Antibody responses were compared with a parallel cohort of children who received 2 doses of BNT162b2 3 weeks apart. Results: From April to May 2022, 59 children with a mean age (SD) of 8.5 years (1.7) were enrolled: 20 CoronaVac and 39 Covilo recipients. The median interval from the primary series was 49 days (IQR 33–51). After booster, the geometric means (GMs) of sVNT and pVNT were 72.2 %inhibition (95 %CI 67.2–77.6) and 499 (95 %CI 399–624), respectively. The proportion of children with sVNT against Omicron strain ≥68 %inhibition increased from none to 70.2 %. The geometric mean ratio (GMR) of sVNT and pVNT compared with a parallel cohort were 4.3 and 12.2, respectively. The GMR of sVNT and pVNT between children who received booster dose at >6-week interval were 1.2 (95 %CI 1.1–1.3). and 1.8 (95 %CI 1.2–2.7) compared with 4–6 weeks interval. Conclusion: A regimen of 2-dose of inactivated vaccine followed by BNT162b2 booster dose elicited high neutralizing antibody against the Omicron variants in healthy school-aged children.

Background: Heterologous prime-boost SARS-CoV-2 vaccination is a widely accepted strategy during the COVID-19 pandemic, which generated a superior immune response than homologous vaccination strategy. Objective: To describe immunogenicity of heterologous prime-boost vaccination with inactivated vaccine, CoronaVac, followed by BNT162b2 and 5-month booster dose with BNT162b2 in healthy Thai adolescents. Methods: Adolescents aged 12–18 years were randomized 1:1:1:1 to receive CoronaVac (SV) followed by BNT162b2 (PZ) 30 or 20 µg at either 3- or 6-week interval (SV3w/PZ30µg, SV3w/PZ20µg, SV6w/PZ30µg or SV6w/PZ20µg). During the Omicron-predominant period, participants were offered a BNT162b2 booster dose 30, 15, or 10 µg. Immunogenicity was determined using IgG antibody against spike-receptor-binding domain of wild type(anti-S-RBD IgG) and surrogate virus neutralization test(sVNT) against Delta variant at 14 days and 5 months after the 2nd dose. Neutralization tests(sVNT and pseudovirus neutralization test; pVNT) against Omicron strain were tested pre- and 14 days post-booster dose. Results: In October 2021, 76 adolescents with a median age of 14.3 years (IQR 12.7–16.0) were enrolled: 20 in SV3w/PZ30µg; 17 in SV3w/PZ20µg; 20 in SV6w/PZ30µg; 19 in SV6w/PZ20µg. At day 14, the geometric mean(GM) of anti-S-RBD IgG in SV3w/PZ30µg was 4713 (95 %CI 4127–5382) binding-antibody unit (BAU)/ml, while geometric mean ratio(GMR) was 1.28 (1.09–1.51) in SV6w/PZ30µg. The GMs of sVNT against Delta variants at day 14 among participants in SV3w/PZ30µg and SV6wk/PZ30µg arm were 95.3 % and 99.7 %inhibition, respectively. At 5 months, GMs of sVNT against Delta variants in SV3w/PZ30µg were significantly declined to 47.8 % but remained at 89.0 % inhibition among SV6w/PZ30µg arm. In April 2022, 52 adolescents received a BNT162b2 booster dose. Proportion of participants with sVNT against Omicron strain > 80 %inhibition was significantly increased from 3.8 % pre-booster to 67 % post-booster. Proportion of participants with pVNT ID50 > 185 was 42 % at 14 days post 2nd dose and 88 % post booster, respectively. Conclusions: Heterologous prime-boost vaccination with CoronaVac followed by BNT162b2 induced high neutralizing titer against SARS-CoV-2 Delta strain. After 5-month interval, booster with BNT162b2 induced high neutralizing titer against Omicron strain.Thai Clinical Trials Registry (thaiclinicaltrials.org): TCTR20210923012.

Primary series vaccination with BNT162b2 followed by a booster 5 months later has been recommended for healthy adolescents. We aimed to describe the immunogenicity in a fractional dose of BNT162b2. Adolescents aged 12–18 years were randomized into six arms for primary series administration: 3wPZ30/30 (reference group), 3wPZ30/20, 3wPZ20/20, 6wPZ30/30, 6wPZ30/20, and 6wPZ20/20 μg. A booster was given at 5 months after the second dose using either 10 or 15 μg of BNT162b2. Immunogenicity following vaccination was determined by IgG against receptor-binding domain (anti-S-RBD IgG; BAU/mL), surrogate virus neutralization test (sVNT; %inhibition) and pseudovirus neutralization (pVNT;ID50) against Omicron. Non-inferiority criteria were defined as a lower boundary of the geometric mean ratio (GMR) being greater than 0.67. From September to October 2021, 118 adolescents with a median age (IQR) of 14.9 years (13.9–16.7) were enrolled. Fourteen days after the primary series, the geometric means (GMs) of anti-S-RBD IgG (BAU/mL) were 3090 (95% CI 2761–3460) in 3wPZ30/30. The GMRs of anti-S-RBD were: 0.80 (95% CI 0.67–0.97) in 3wPZ30/20; 1.00 (95% CI 0.83–1.20) in 3wPZ20/20; 1.37 (95% CI 1.13–1.65) in 6wPZ30/30; 1.24 (95% CI 1.02–1.50) in 6wPZ30/20; and 1.36 (1.13–1.64) in 6wPZ20/20. After a booster dose with 15 μg (n = 24) of BNT162b2, sVNT and pVNT against Omicron variant were 91.6 (95% CI 88.4–94.9) and 331 (95% CI 221–495), respectively. In the group that received 10 μg of BNT162b2 (n = 25), sVNT was 85.6 (95% CI 80.0–91.6) and pVNT was 397 (95% CI 267–590). Healthy adolescents had good immune responses to the fractional dose regimen of BNT162b2 and this may be considered as an alternative option.

Despite the BNT162b2 vaccination coverage, rapid transmission of Omicron SARS-CoV-2 has occurred, which is suspected to be due to the immune escape of the variant or waning vaccine efficacy of multiple BNT162b2 vaccination doses. Our study aims to compare immunogenicity against Omicron prior to and post a booster dose of BNT162b2 in healthy adolescents, and to evaluate their attitudes toward booster dose vaccination. A cross sectional study was conducted among healthy adolescents aged 12–17 who received two doses of BNT162b2 more than 5 months ago. Participants and their guardians performed self-reported questionnaires regarding reasons for receiving the booster. A 30 ug booster dose of BNT162b2 was offered. Immunogenicity was evaluated by a surrogate virus neutralization test (sVNT) against the Omicron variant, and anti-spike-receptor-binding-domain IgG (anti-S-RBD IgG) taken pre-booster and 14-days post-booster. From March to April 2022, 120 healthy Thai adolescents with a median age of 15 years (IQR 14–16) were enrolled. sVNT against Omicron pre- and post-booster had 11.9 (95%CI 0–23.9) and 94.3 (90.6–97.4) % inhibition. Geometric means (GMs) of anti-S-RBD IgG increased from 837 (728, 953) to 3041 (2893, 3229) BAU/mL. Major reasons to receive the booster vaccination were perceived as vaccine efficacy, reduced risk of spreading infection to family, and safe resumption of social activities. A booster dose of BNT162b2 elicits high immunogenicity against the Omicron variant. Motivation for receiving booster doses is to reduce risk of infection.

Adolescents with underlying diseases are at risk of severe COVID-19. The immune response of BNT162b2 may be poor among immunocompromised adolescents. We aim to describe immunogenicity of mRNA BNT162b2 among adolescents who are immunocompromised or have chronic diseases. We recruited adolescents 12–18 years of age; group A impaired-immunity (post-transplantation, cancer, on immunosuppressive drugs) and group B chronic diseases. A two-dose regimen of BNT162b2 was given. Immunogenicity was determined by surrogate virus neutralization test (sVNT) and IgG against receptor-binding domain (RBD). From August to October 2021, 312 adolescents, with a median age (IQR) of 15 years (13.7–16.5), were enrolled (group A 100, group B 212). The geometric means (GMs) of sVNT (% inhibition) against Delta strain and anti-RBD IgG (BAU/mL) after the 2nd dose among group A were: post-transplantation recipients 52.9 (95% CI 37.7–74.2) and 233.6 (95% CI 79–690.6); adolescents with cancer 62.3 (95% CI 29.2–133.1) and 214.9(95% CI 34.2–1348.6); and adolescents with other immunosuppressive conditions 66.7 (95% CI 52.4–84.8) and 849.8 (95% CI 393.4–1835.8). In group B were: adolescents living with HIV 98 (95% CI 97.3–98.8) and 3240.3 (95% CI 2699–3890.2), and adolescents with other chronic disease 98.6 (95% CI 98.3–98.9) and 3818.5 (95% CI 3490.4–4177.4). At day 90, immunity declined; among impaired-immunity participants were 43.9 (95% CI 30.8–62.4) and 178.7 (95% CI 91.2–350.1) and adolescents with chronic diseases were 90.6 (95% CI 88.4–92.8) and 1037.1 (95% CI 933.3–1152.5). In conclusion, adolescents with impaired immunity had a poor response to 2-doses of BNT162b2, additional dose should be considered. Adolescents with chronic diseases had excellent response but immunity waned after 3 m, booster dose may be required.

Inactivated SARS-CoV-2 vaccine (CoronaVac) is commonly used in national immunization programs. However, the immune response significantly declines within a few months. Our study assessed the immune response against SARS-CoV-2 after receiving booster shots of BNT162b2 or ChAdOx1 among health care workers who previously received CoronaVac as their primary immunization. Fifty-six participants who received ChAdOx1 and forty-two participants who received BNT162b2 were enrolled into this study, which evaluated immune responses, including anti-SARS-CoV-2 spike total antibodies (Elecsys®), surrogated viral neutralization test (sVNT) to ancestral strain (cPass™; GenScript), five variants of concern (Alpha, Beta, Gamma, Delta, and Omicron) (Luminex; multiplex sVNT) and the ELISpot with spike (S1 and S2) peptide pool against the ancestral SARS-CoV-2 strain. The samples were analyzed at baseline, 4, and 12 weeks after primary immunization, as well as 4 and 12 weeks after receiving the booster. This study showed a significant increase in anti-SARS-CoV-2 spike total antibodies, sVNT, and T-cell immune response after the booster, including against the Omicron variant. Immune responses rapidly decreased in the booster group at 12 weeks after booster but were still higher than post-primary vaccination. A fourth dose or a second booster should be recommended, particularly in health care workers.

Background: Children aged 6 months to 4 years have been recommended to receive three doses of BNT162b2, after COVID-19 infection, to immunize against SARS-CoV-2. Therefore, they might need fewer doses of vaccine compared with COVID-naïve children. Objective: To describe the immunogenicity of 2-dose BNT162b2 following COVID-19 in healthy young children previously infected with SARS-CoV-2. Materials and Methods: A prospective cohort study was conducted among children aged 6 months to 4 years who had SARS-CoV-2 infection during Delta-variant, which was July to November 2021, or Omicron-variant-predominant eras, which was February to August 2022. Participants received two doses of intramuscular BNT162b2 at an 8-week interval. Neutralizing antibodies against SARS-CoV-2 Omicron variant BA.4/5 were measured using pseudovirus neutralization tests (pVNT; ID50) at baseline and 28 days after the second dose. Results were compared with a parallel cohort of COVID-naïve children who received 3-doses of BNT162b2 at 0, 4 and 12 weeks. Results: Between November and December 2022, 80 children with a median age of 2.9 years (IQR 2.1 to 3.8) were enrolled. The median time from COVID-19 infection to the first dose was 13.8 months (IQR 13.8 to 16.2) in the Post-Delta Group, and 8.0 months (IQR 3.7 to 8.2) in the Post-Omicron Group. After 2-doses of BNT162b2, the geometric means (GMs) of pVNT increased from 105 (95% CI 48 to 231) to 863 (95% CI 638 to 1,168) in the Post-Delta Group and from 264 (95% CI 192 to 361) to 2,268 (95% CI 1,831 to 2,811) in the Post-Omicron Group. In comparison, the GM of pVNT was 59 (95% CI 31 to 114) in the parallel cohort of COVID-naïve children who received 3-doses of BNT162b2. Conclusion: Two doses of BNT162b2 were able to boost the immune response with high neutralizing antibodies against the circulating Omicron variant in children who were previously infected with SARS-CoV-2. [ABSTRACT FROM AUTHOR]