The Oxford Covid vaccine is more effective when the second dose is delayed, according to the UK medicines regulator, with the Government’s expert vaccine committee adding that this is likely to also be the case for the Pfizer vaccine.
Regulatory documents filed by the Medicines and Healthcare products Regulatory Agency (MHRA) said there was ‘more certainty’ of the efficacy of Oxford/AstraZeneca Covid-19 vaccine if the second dose is delayed by eight to 12 weeks after the first.
And documents published by the Joint Committee on Vaccination and Immunisation (JCVI) this afternoon added that there was ‘no strong reason’ to believe the Pfizer/BioNTech vaccine would be any different.
The MHRA has authorised the Oxford/Astra Zeneca vaccine to be given as two doses, separated by four to 12 weeks, and the Pfizer one at two doses between three to 12 weeks.
However, in regulatory documents it has drawn up for healthcare professionals the MHRA said its analysis revealed ‘increased immunogenicity was associated with a longer dose interval’.
It said that giving the second dose eight to 12 weeks after the first provided a more certain immune response.
Oxford University, which developed the vaccine, has also noted the MHRA’s finding about longer intervals between doses ‘may translate into better protection’.
It comes after the UK’s four chief medical officers changed their advice about prolonging the interval between the two doses of the Pfizer/BioNTech vaccine.
GPs are now recommended to delay the second dose by up to 12 weeks – when initially they had been told to give it after three weeks.
The MHRA’s regulatory documents on the Oxford/AstraZeneca Covid-19 vaccine, published this week, said: ‘Exploratory analyses showed that increased immunogenicity was associated with a longer dose interval.
‘Efficacy is currently demonstrated with more certainty for dose intervals from 8 to 12 weeks. Data for intervals longer than 12 weeks are limited.’
Information published by Oxford University in an FAQ said: ‘Our interim results show that the vaccine works well, after the second dose, with an interval of between four and twelve weeks as licensed by MHRA. The MHRA have reviewed the data and believe that the protection is most robust when the booster dose is delivered between four and twelve weeks.
‘The data suggest that a longer interval between doses may increase the effectiveness of the vaccine after the second dose. However more data from the trials will provide greater certainty about this effect.’
It later added: ‘The MHRA label shows that the immune response is stronger with longer intervals between the two doses, and this may translate into better protection.’
Meanwhile, the JCVI report on the new dose regimen said: ‘With most vaccines an extended interval between the prime and booster doses leads to a better immune response to the booster dose. There is evidence that a longer interval between the first and second doses promotes a stronger immune response with the AstraZeneca vaccine.
‘There is currently no strong evidence to expect that the immune response from the Pfizer-BioNTech and AstraZeneca vaccines differ substantially from each other.’