Fourth, this study only included BNT162b2 vaccine recipients. 17. We shown that only 38.2% of BNT162b2 vaccine recipients and 26.7% of recovered COVID-19 individuals experienced their serum neutralization titre at or above the Acolbifene (EM 652, SCH57068) detection threshold in our live virus microneutralization assay. Furthermore, the neutralizing antibody titer against the Omicron variant was considerably Acolbifene (EM 652, SCH57068) lower than those against the ancestral disease or the Beta variant. Our results suggest that vaccine recipients and COVID-19 individuals in the pediatric age group will likely be more susceptible to vaccine breakthrough infections or reinfections due to the Omicron variant than earlier variants. value of 0.05 was considered statistically significant. Results This study included serum specimens from a total of 49 individuals, of whom 34 were COVID-19 vaccine recipients, and 15 were recovered COVID-19 individuals. All COVID-19 vaccine recipients were aged 12 years or above, because children aged 11 years or below were not included in the recommended group for the COVID-19 vaccine in Hong Kong SAR at the time of writing. All have received two doses of BNT162b2 vaccine, and the serum samples were collected at a median of 26.5 days after the first dose (range 24C87 days), and at a median of four days after the second dose (range 3C65 days). For recovered COVID-19 individuals, their age ranged from 2.6 to 17.9 years old (Table 1). These recovered individuals were 1st diagnosed to have COVID-19 between November 2020 and January Acolbifene (EM 652, SCH57068) 2021, and their serum samples were collected at a median of 44 days after the 1st laboratory analysis (range 29C96 days). Four of these individuals were infected with the B.1.36.27 lineage. The disease lineage information is not available for the 11 additional individuals, but they are likely infected with the B.1.36.27 lineage, which was the main lineage circulating in Hong Kong during this period [22]. Table 1. Demographics and medical info of recovered COVID-19 individuals and vaccine recipients. value /th /thead Female sex, no. (%)6 (17.6%)10 (66.7%)0.002aMedian age in years (range)15.0 (12.7C17.9)9.6 (2.6C17.9)0.001bSymptomatic, no. (%)N/A14 (93.3%)N/A Open in a separate window Notice: N/A, Not applicable. aFishers precise FLJ32792 test. bMann Whitney U test. All recovered COVID-19 individuals and vaccine recipients experienced an MN titer of 10 against the ancestral lineage A disease. Similarly, 94.1% (32/34) of vaccine recipients and all recovered individuals had MN titer of 10 against the Beta variant. However, only 38.2% (13/34) and 26.7% (4/15) of vaccine recipients and recovered individuals had an MN titer of 10 against the Omicron variant, respectively. The geometric mean microneutralization antibody titer (GMT) against the Omicron variant (Vaccine recipients: 7.2 [95% CI, 6.0C8.6]; Recovered individuals: 6.3 [95% CI, 5.0C8.0]) was significantly lower than those Acolbifene (EM 652, SCH57068) against the ancestral disease (Vaccine recipients: 150.5 [95% CI, 109.6C206.7]; Recovered individuals:127.0 [95% CI, 96.2C167.7]) or the Beta variant (Vaccine recipients: 49.05 [95% CI, 33.6C71.7]; Recovered individuals: 41.9 [95% CI, 28.2C62.3]) for both vaccine recipients and recovered COVID-19 individuals (Number 1). Relative to the ancestral lineage A disease, there was a significantly higher fold reduction for Omicron variant than those for the Beta variant for both vaccine recipients and recovered individuals ( em P /em ? ?0.0001) (Number 2). However, there was no statistically significant difference in the collapse reduction between vaccine recipients and recovered individuals for both Beta and Omicron variants. Figure 1. Assessment of microneutralization antibody (MN) titers between the Omicron variant and additional variants or ancestral SARS-CoV-2 disease. Vaccine recipients (early): serum specimens collected from 34 vaccine recipients at a median of four Acolbifene (EM 652, SCH57068) days after the 2nd dose. Vaccine recipients (late): serum specimens collected from 21 vaccine recipients at a median of 44 days after the 2nd dose. Open circles represent the MN titer of each serum specimen. The MN titers from your same patient were connected from the dotted collection. *** em P /em ? ?0.001; **** em P /em ? ?0.0001. Number 2. Fold reduction of microneutralization antibody.