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In the era of globally predominant omicron strains, a COVID-19 booster vaccine is needed. Our study aimed to evaluate the immunogenicity of a half-dose BNT162b2 booster after AZD1222 in healthy adults. A randomized trial of volunteers aged 18–69 years who received two-dose AZD1222 was conducted. The participants were randomized to receive the BNT162b2 vaccine intramuscularly—half (15 µg) vs. standard dose (30 µg). The immunogenicity was evaluated by a surrogate virus neutralization test (sVNT) against omicron variants and anti-spike-receptor-binding-domain IgG (anti-S-RBD IgG). From November–December 2021, 100 adults with a median age of 59.3 years (IQR 33.4–65.5) were enrolled. A booster dose was given at median of 98 days (IQR 92–128) after AZD1222. At day 14, the geometric means (GMs) of anti-S-RBD IgG in half- vs. standard-dose group were 2329.8 vs. 2574.7 BAU/mL, with a geometric mean ratio (GMR) of 0.90 (0.77–1.06). The GMs of sVNT against the omicron variant in the half- and standard-dose groups were 74.4% inhibition (95% CI 68.8–80.5) and 67.3% inhibition (57.9–78.1), respectively, with GMR of 0.95 (0.69–1.30). At day 90, the sVNT indicated 22.3% inhibition (95% CI 14.9–33.4) and 20.4% inhibition (13.1–32.0), respectively, with GMR of 1.09 (0.60–1.98). The fractional low-dose BNT162b2 mRNA booster vaccine provided non-inferior immunogenicity responses. During a shortage of vaccine supply, a fractional low dose should be considered for a booster vaccination program.

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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 ug (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.

<b><i>Introduction:</i></b> Food allergy is the major cause of pediatric anaphylaxis. Characteristics and triggers may be different in different geographical regions. Studies focusing on food-induced anaphylaxis (FIA) in Asian developing countries are limited. Our study aimed to study characteristics of FIA in a tertiary care center in an Asian developing country. <b><i>Methods:</i></b> Retrospective review of pediatric anaphylaxis admission and outpatient visit at a tertiary care hospital in Bangkok, Thailand during 2008–2018 was performed. Data regarding clinical presentation, place reaction occurred, time of onset, investigations (serum tryptase, specific immunoglobulin E, and skin test), treatment, and follow-up periods were collected. <b><i>Results:</i></b> One hundred seventy-four anaphylaxis admission records of which 61 episodes of FIA were retrieved. Data from outpatients visit consisted of 17 patients. Most patients were male (76.7%). The median age was 7.1 years (interquartile range 1.9–12.4). The major causes of FIA were shrimp/shellfish (37%), wheat (15.1%), and cow’s milk (11%). Food causing anaphylaxis varied according to age-group: infants had anaphylactic reactions to egg, wheat, and cow’s milk, preschools to wheat and peanut, and older children to shrimp/shellfish. Cutaneous manifestations occurred in all patients, followed by lower respiratory tract symptoms (83.6%) and gastrointestinal symptoms (50.8%). There was no biphasic anaphylaxis reported. Elevated serum tryptase was found in only 4 patients (7%). <b><i>Conclusion:</i></b> Recognizing characteristics of pediatric FIA is crucial. The common causes of FIA in our study in Asian children were egg in infants, wheat and peanut in preschool children, and shrimp/shellfish in school-age children and adolescents. Skin manifestation presented in all patients with FIA.

Background Currently, booster dose is needed after 2 doses of inactivated COVID-19 vaccine. With limited resource and shortage of COVID-19 vaccine, intradermal(ID) administration might be a potential dose-sparing strategy. Objective To determine antibody response and reactogenicity of ID ChAdOx1 nCoV-19 vaccine(AZD1222,Oxford/AstraZeneca) as a booster dose after completion of 2-dose CoronaVac(SV) in healthy adult. Methods This is a prospective cohort study of adult aged 18-59 years who received 2-dose SV at 14-35 days apart for more than 2 months. Participants received ID AZD1222 at fractional low dose(1x1010 viral particles,0.1ml). Antibody responses were evaluated by surrogate virus neutralization test(sVNT) against wild type and delta variant and anti-spike-receptor-binding-domain immunoglobulin G(anti-S-RBD IgG) at prior, day14 or 28, and day90 post booster. Solicited reactogenicity was collected during 7 days post-booster. Primary endpoint was the differences of sVNT against delta strain ≥80%inhibition at day14 and 90 compared with the parallel cohort study of 0.5-ml intramuscular(IM) route. Results From August2021, 100 adults with median(IQR) age of 46(41-52) years participated. At baseline, geometric means(GMs) of sVNT against delta strain prior to booster were 22.4%inhibition(95%CI 18.7-26.9) and of anti-S-RBD IgG were 109.3(95.4-125.1)BAU/ml. GMs of sVNT against delta strain were 92.9%inhibition(95%CI 87.7-98.3) at day14 and 73.1%inhibition(66.7-80.2) at day90 post ID booster. The differences of proportion of participants with sVNT to delta strain≥80%inhibition in ID recipients versus IM were +4.2%(95%CI-2.0to10.5) at day14, and -37.3%(-54.2to-20.3) at day90. Anti-S-RBD IgG GMs were 2037.1(95%CI1770.9-2343.2) at day14 and 744.6(650.1-852.9) BAU/ml at day90, respectively. Geometric mean ratios(GMRs) of anti-S-RBD IgG were 0.99(0.83-1.20) at day14, and 0.82(0.66-1.02) at day90. Only 18% reported feverish, compared with 37% of IM(p=0.003). Only 18% reported feverish, compared with 37% of IM(p=0.003). Common reactogenicity was erythema(55%) at injection site while 7% reported blister. Conclusion Low-dose ID AZD1222 booster enhanced lower neutralizing antibodies at 3 months compared with IM route. Less systemic reactogenicity occurred, but higher local reactogenicity.

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