‘A study (preprint for The Lancet) of data from the Phase 3 clinical trials of the AstraZeneca-Oxford University vaccine evaluated vaccine efficacy after a single dose and for alternate timing for the booster dose. Notably, the UK adapted the timing for the booster dose from 4 weeks after the first dose—which is how the vaccine was designed to be administered and the timing used for clinical trials—to 12 weeks in an effort to provide the first dose to as many people as possible. This study assessed the vaccine’s efficacy in participants who received the 2 doses between 4 and 12 weeks apart.
‘The researchers found that the efficacy after the first dose did not wane in the first 12 weeks. A single dose of the vaccine was 76% efficacious in preventing symptomatic COVID-19 disease in the first 90 days after vaccination, although it was associated with a substantial decrease in efficacy with respect to preventing asymptomatic infection. Notably, however, the additional asymptomatic infections could potentially be among participants who would have otherwise developed COVID-19 symptoms. Additionally, the efficacy in preventing symptomatic disease was higher in participants who received the booster dose later than in those who received it earlier. Vaccine efficacy was 82.4% among participants who received their booster dose 12 weeks or longer after the first dose, compared to 54.9% in those who received their 2 doses less than 6 weeks apart. These results provide support for vaccination plans that delay the booster dose beyond the intended 4 weeks, considering that the immunity conferred after the first dose appears to be relatively stable over the first several months and the overall protection appears to increase with an increased time between the prime and booster doses.
‘The researchers also found that vaccination was associated with an overall reduced risk of infection—54.9% efficacy for 2 doses and 67% efficacy for 1 dose—which provides evidence that the vaccine could also provide protection against SARS-CoV-2 transmission. The role of SARS-CoV-2 vaccines in mitigating transmission risk remains uncertain, but these findings provide a promising indication that vaccination could reduce community spread of the virus, which would be a major tool to bring the pandemic under control.’
**The above summary was contained in an update of Feb 5, 2021, on the COVID-19 pandemic from the Johns Hopkins Center for Health Security
- Single dose administration, and the influence of the timing of the booster dose on immunogenicity and efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine
Read here (The Lancet, Feb 1, 2021)
