According to a new study, an interval of three months between the administration of the first dose and the second dose of AstraZeneca’s Covid-19 vaccine may yield better efficacy.
The study, published in the journal Lancet, suggested that the first dose could offer 76 per cent protection against the coronavirus if the second dose was inoculated after three months.
For the research, the authors carried out post-hoc exploratory analyses from a phase three randomised controlled trial. The trials found that the interval between doses can be safely extended to 3 months given the protection a single dose offers. This may also allow countries to vaccinate a larger proportion of the population more rapidly.
Study lead author Professor Andrew Pollard, University of Oxford, United Kingdom (UK), said, "Vaccine supply is likely to be limited, at least in the short term, and so policy-makers must decide how best to deliver doses to achieve the greatest public health benefit.”
He added, “Where there is a limited supply, policies of initially vaccinating more people with a single dose may provide greater immediate population protection than vaccinating half the number of people with 2 doses. In the long term, a second dose should ensure long-lived immunity, and so we encourage everyone who has had their first vaccine to ensure they receive both doses."
Other vaccines, including for flu, Ebola and malaria, also give greater protection and stronger immune responses after a longer interval between doses.
Methodology
For this study, the researchers combined data from randomized controlled trials in the UK, Brazil, and South Africa, including 8,948, 6,753, and 1,477 people, respectively (totaling 17,178 people).
Participants were aged 18 years and over (see appendix table S1 for more detail), and either received two standard doses of the Oxford Covid-19 vaccine (8,597 participants) or a control vaccine/saline placebo (8,581).
In the UK trial, a subset of participants (1,396 people) received a lower dose of the vaccine than their first dose.
The primary outcome of the trial was the number of symptomatic Covid-19 cases in the control and Covid-19 vaccine groups occurring more than 14 days after the second dose.
Findings
The results revealed that participants who were given their doses 12 or more weeks apart had greater protection (81 per cent) than people who were given their two doses less than 6 weeks apart (55 per cent).
Following a single standard vaccine dose, vaccine efficacy from 22 days to three months after vaccination was 76 per cent. Their modeling further indicated that this protection did not reduce over the 3 months.
Notably, antibody levels against the SARS-CoV-2 spike protein remained at similar levels for 3 months.