Three month gap between Oxford vaccine jabs provides better efficacy
A three-month interval between doses of the Oxford COVID-19 vaccine results in higher vaccine efficacy compared to a six-week gap, according to a new study which says the first dose can offer up to 76 percent protection in the months between the two jabs. The results of the analysis from a Phase III randomized controlled trial were published in The Lancet journal.
Dosage regimen can prove beneficial during limited vaccine supply
The study results suggest that the interval between doses can be safely extended to three months given the protection a single dose offers. According to the researchers, including those from the University of Oxford, this dosage regimen is beneficial while vaccine supplies are initially limited, and may allow countries to immunize a larger proportion of the population more rapidly.
Second dose will provide long-lived immunity
"Vaccine supply is likely to be limited, at least in the short-term, and so policy-makers must decide how best to deliver doses," said study lead author Professor Andrew Pollard. "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," he added.
For immediate protection, more people should be given single dose
Pollard, from the University of Oxford, believes that policies of initially vaccinating more people with a single dose may provide greater immediate population protection than immunizing half the number of people with two doses, especially in places where the Oxford vaccine is in limited supply.
Data from clinical trials held in four countries were combined
Researchers combined data from clinical trials in the UK, Brazil, and South Africa, which together included a total of 17,178 adult participants. According to the researchers, these participants either received two standard doses of the Oxford COVID-19 vaccine, or a control vaccine/saline placebo. In the UK trial, they said a subset of participants received a lower dose of the vaccine than their first dose.
Researchers studied the effect different intervals had on protection
From the study, researchers sought to understand the effect of different intervals on protection after the second dose, and the risk of infection between jabs - either due to lower efficacy of a single dose or rapid waning of efficacy while waiting for the second.
The basis on which participants were assessed
To evaluate the efficacy of a single dose, the authors assessed participants who had taken their first standard dose but tested positive for COVID-19 more than 21 days afterward. According to the scientists, participants who were given their doses 12 or more weeks apart had greater protection than people given their two doses less than six weeks apart.
Binding-antibody response higher in those with longer delay between jabs
Researchers said that the efficacy results were supported by immune response results in the participants, which found that binding-antibody responses were more than two-fold higher in the group having their two vaccines with a longer delay. After receiving a single standard dose, the researchers said that the vaccine efficacy in the participants from 22 days to three months after the immunization was 76 percent.
How long does a single dose offer protection?
Researchers said, "Modelling analysis indicated that this protection did not reduce over the three-months. According to the study, the antibody levels against the SARS-CoV-2 spike protein remained at similar levels for three months. However, the scientists said it is not yet clear how long protection with a single dose of the vaccine might last, since the trial results are limited to three months.
