O-10554

The CoronaVac vaccine is widely used in Thailand to combat the coronavirus disease 2019 (COVID-19) pandemic. The limited immunogenicity of this vaccine is a concern, especially because of expanding delta variant outbreaks. A third boost may enhance antiviral immune responses.

This non-inferiority randomized controlled trial evaluated the immunogenicity and safety of an intradermal (ID) fractional third dose of AZD1222 vaccine compared with those of a standard intramuscular (IM) third dose. Participants were enrolled from August 9, 2021 to August 13, 2021 at Chulabhorn Hospital, Bangkok, Thailand. The eligibility criteria were age 18 years or older and prior two-dose Coronavac vaccination completed at least 2 months previously. Participants were randomly assigned to one of three groups by block randomization: (i) standard dose by IM administration (IM), (ii) 20% of the standard dose ID (ID1), or (iii) 40% of the standard dose ID (ID2). The primary endpoint was the geometric mean ratio of anti-receptor binding domain antibody in the ID1/ID2 vs. the IM groups 14 days post-vaccination.

A total of 125 participants were randomized (IM, n = 41; ID1, n = 41; and ID2, n = 43). One participant was lost to follow-up by day 14 post-vaccination in the ID1 group. The geometric mean ratio (95% confidence interval) of anti-receptor binding domain antibody was 0.94 (0.80-1.09) in the ID1 group and 1.28 (0.95-1.74) in the ID2 group. Immunogenicity in both ID groups met the non-inferiority criteria. Local adverse events were more common in the ID groups than in the IM group but were mostly mild to moderate in severity.

An ID fractional third dose of AZD1222 was non-inferior to a standard IM third dose among individuals previously vaccinated with CoronaVac. Adverse events associated with the ID fractional third dose included mild to moderate local site reactions. This vaccination strategy may help conserve vaccine supply.

Biological molecules isolated from organisms that live under subzero conditions could be used to protect oocytes from cryoinjuries suffered during cryopreservation. This study examined the cryoprotectant role of exopolysaccharides of Pseudomonas sp. ID1 (EPS ID1) in the vitrification of prepubertal and adult cow oocytes. IVM oocytes were vitrified and warmed in media supplemented with 0, 1, 10, 100 or 1000µgmL−1 EPS ID1. After warming, oocytes were fertilised and embryo development, spindle morphology and the expression of several genes in Day 8 blastocysts were assessed. Vitrification led to significantly lower proportion of prepubertal oocytes exhibiting a normal spindle configuration. In fresh control oocytes and most groups of vitrified adult oocytes, similar percentages of oocytes with a normal spindle configuration were observed. Percentages of Day 8 blastocysts were similar for prepubertal oocytes vitrified in the absence or presence of 1 or 10µgmL−1 EPS ID1 and for adult oocytes vitrified in the presence of 10µgmL−1 EPS ID1 compared with non-vitrified oocytes. EPS ID1 supplementation had no effect on solute carrier family 2 member 3 (SLC2A3), ubiquitin-conjugating enzyme E2A (UBE2A) and histone deacetylase 1 (HDAC1) expression in Day 8 blastocysts form adult oocytes. However, supplementation with 10 and 100µgmL−1 EPS ID1 led to increased expression of genes involved in epigenetic modifications (DNA methyltransferase 3 alpha (DNMT3A) and K (lysine) acetyltransferase 2A (KAT2A)) and apoptosis (BCL2 associated X apoptosis regulator (BAX) and BCL2-like 1 (BCL2L1)). The lowest BAX:BCL2L1 ratio was found in the 10µgmL−1 EPS ID1-supplemented group. The results suggest that 10µgmL−1 EPS ID1 added to vitrification and warming media may help protect bovine oocytes against cryodamage.