Tolerability and Immunogenicity After a Late Second Dose or a Third Dose of ChAdOx1 nCoV-19 (AZD1222)

Immunogenicity of Oxford-AstraZeneca COVID-19 vaccine in Vietnamese healthcare workers

“…However, the data also emphasize the importance of the second dose [15], especially in older people, while it remains unknown whether the third dose is needed to provide long-term protection. A decline in antibody titers was recorded at week 8-12 after the first two doses among 75 study participants in the UK [16]. But the administration of the third dose helped boost the immune response.…”

Low dose prime and delayed boost can improve COVID-19 vaccine efficacies by increasing B cell selection stringency in germinal centres

“…The higher efficacies observed above are thus argued to be due to the improved quality and quantity of the antibodies produced by the associated dosing protocols (5,8,9,11,21). For instance, higher antibody levels were observed following the boost upon increasing the dosing interval (9,10). In some cases, antibodydependent cellular functions too appeared to be better with the longer intervals (21).…”

“…While the role of cellular immunity is yet to be fully elucidated (14), several studies suggest that the efficacy of currently approved COVID-19 vaccines is attributable to the neutralizing antibodies they elicit (6,11,(15)(16)(17)(18)(19)(20). The higher efficacies observed above are thus argued to be due to the improved quality and quantity of the antibodies produced by the associated dosing protocols (5,8,9,11,21). For instance, higher antibody levels were observed following the boost upon increasing the dosing interval (9,10).…”

“…With the Oxford-AstraZeneca vaccine, where dosing protocols were adjusted during the trials, data has become available of the effects of different dosages used for the prime and boost doses and of different intervals separating them on vaccine efficacy (5)(6)(7)(8). A recent study has also examined the effects of increasing the interval beyond those in the trials (9). Intriguingly, the efficacy in preventing symptomatic infection was 63.1% when a standard dose (containing 5×10 10 virus particles) was used for both prime and boost, whereas the efficacy was substantially higher, 80.7%, when a low dose prime (containing 2.2×10 10 virus particles) followed by the standard dose boost was administered (5).…”

Covid-19: Third vaccine dose boosts immune response but may not be needed, say researchers

“…In a preprint, published on 28 June,1 researchers from the University of Oxford reported that extending the interval between the first and second dose to 45 weeks resulted in higher antibody titres. They also found that a third dose given 44 to 45 weeks after the second increased antibody titres further, and that adverse events were lower after the second or third dose than after the first.…”