February 20, Kathmandu
A three-month interval between doses of the Oxford COVID-19 vaccine results in higher vaccine efficacy than 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.
According to the researchers, including those from the University of Oxford in the UK, 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.
"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," said study lead author Professor Andrew Pollard from the University of Oxford.
"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.
From the study, the researchers try to understand the effect of intervals between the second dose and the risk of infection between gaps.
However, they have 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.
They also estimated the impact of one or two doses of the vaccine on reducing COVID-19 cases as an indicator of how the vaccine might help to reduce transmission in the community.
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.
They mentioned better efficacy results were mostly supported by the immune and antibody that one contains.
According to the scientists, participants who were given doses apart in 12 weeks had more effective protection than people who had taken two doses less than six weeks apart.
After receiving a single standard dose, the researchers said the vaccine efficacy in the participants from 22 days to three months after the immunization was 76 percent.
Modeling analysis indicated that this protection did not reduce over the three months, they added.
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.
So they still recommend a second dose of the vaccine.
"This latest analysis confirms our previous findings of the higher efficacy of a low- then standard-dose regimen," said study co-author Merryn Voyse from the University of Oxford.
"However, with additional data available, we have found that the enhanced efficacy and immunity may be partly driven by the longer interval between doses that were common in this trial group," Ms. Voyse said.
She believes the findings further support the relationship between vaccine interval and efficacy in those receiving two standard doses.