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The interval between doses of the Oxford/Astra Zeneca vaccine for all age groups in now 12 weeks, according to updated guidance from the National Immunisation Advisory Committee (NIAC).
Previously NIAC had advised that, for those older than 65, a two-dose scheduling interval of four to six weeks was recommended, while for those less than 65 years of age, an interval of four to 12 weeks was endorsed.
Evidence shows that a higher vaccine efficacy of 82 per cent after the second dose is achieved if the booster dose was given at 12 weeks.
On 25 February NIAC issued updated advise stating the change for the Covid-19 vaccine, which is currently being administered to healthcare workers.
A decision was made by NIAC in January to administer mRNA vaccines to the over 70s in favour of the Oxford/Astra Zeneca vaccine, as there was insufficient clinical trial data to determine efficacy in those aged 55 and older.
The preference was recommended despite the European Medicines Agency (EMA) advising that the vaccine could be used in older adults.
This is because a similar immune response was found in all age groups during trials, meaning it is expected that a fall in Covid-19 will be achieved in older age groups.
The vaccine was licensed by manufacturers for administration at an interval of four to 12 weeks based on immunogenicity and efficacy data.
Evidence shows that protection starts from about three weeks after the first vaccine dose and lasts up to 12 weeks.
“Studies show 76 per cent protection overall against symptomatic Covid-19 disease in the first 90 days. Modelling showed no evidence of waning of protection in the first three months after vaccination,” according to the NIAC document, clinical guidance for Covid-19 vaccination.
It adds that when the vaccine is being administered in pregnancy, the two dose schedule should be given 12 weeks apart if possible.
“However, as the two dose schedule should be given between 14 and 33 completed weeks of gestation, a shorter interval can be used, 4-12 weeks apart.”