Rollout of second COVID-19 vaccine begins amid move to new dosing strategy

Patients have this week started receiving the second COVID-19 vaccine to be authorised for UK supply, as vaccination strategy shifts to maximise the number of vulnerable people given a single dose.

Prescribing information for the Oxford/AstraZeneca COVID-19 vaccine says the second dose should be administered between 4 and 12 weeks after the first dose. | GETTY IMAGES
Prescribing information for the Oxford/AstraZeneca COVID-19 vaccine says the second dose should be administered between 4 and 12 weeks after the first dose. | GETTY IMAGES

The newest vaccine, developed by the University of Oxford and AstraZeneca, uses a modified adenovirus vector to introduce the gene for the SARS-CoV-2 spike protein into the body. It was approved on 30th December, with 82-year-old Brian Pinker becoming the first patient to receive a dose outside clinical trials at 7.30am on Monday 4 January at Oxford's Churchill Hospital.

The DHSC has confirmed that 500,000 doses of the Oxford/AstraZeneca vaccine are available to be administered this week, and a similar number of the Pfizer/BioNTech vaccine are reportedly also ready for rollout this week.

The Oxford/AstraZeneca vaccine does not require storage at -70°C like the mRNA-based Pfizer jab, making it easier to transport and store. An updated version of NHS England's COVID-19 vaccination standard operating procedure recommends that PCN vaccination sites use the Oxford/AstraZeneca vaccine in smaller care homes and for housebound patients. The SOP suggests that the 15-minute observation period recommended for the Pfizer vaccine will also apply to the Oxford/AstraZeneca jab. 

Vaccination strategy

At the same time as authorisation of the Oxford/AstraZeneca vaccine, the DHSC announced a change recommended by the JCVI to focus UK vaccination strategy on administering a first dose of either of the two authorised vaccines to as many patients in at-risk groups as possible, with second doses postponed for up to 12 weeks.

The UK's four CMOs said in a letter to the profession on 31 December that 'in terms of protecting priority groups, a model where we can vaccinate twice the number of people in the next 2–3 months is obviously much more preferable in public health terms than one where we vaccinate half the number but with only slightly greater protection'.

'We are confident that based on publicly available data as well as data available to the JCVI that the first dose of either Pfizer or AstraZeneca vaccine provides substantial protection within 23 weeks of vaccination for clinical disease, and in particular severe COVID disease', they said.

The CMOs said they recognised that the request to re-schedule second appointments is operationally challenging, especially at short notice, and will distress patients who were looking forward to being fully immunised.

They added: 'However, we are all conscious that for every 1,000 people boosted with a second dose of COVID-19 vaccine in January (who will as a result gain marginally on protection from severe disease), 1,000 new people can’t have substantial initial protection which is in most cases likely to raise them from 0% protected to at least 70% protected.'

JCVI advice

The CMOs' letter included an evidence statement from the JCVI noting that short-term efficacy was around 90% for the Pfizer/BioNTech vaccine and 70% for the Oxford/AstraZeneca vaccine.

The statement said that, taking into account the seven days after the Pfizer second dose was administered when it would not be expected to provide additional protection, its phase 3 trial showed vaccine efficacy of about 90% 'from two weeks after the first dose and for the following two weeks'.

'It does not indicate [efficacy] beyond this time point as participants had received a second dose,' the JCVI added.

Protection from a single dose of the Oxford/AstraZeneca vaccine was assessed in an exploratory analysis, which 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,' the JCVI said. Prescribing information for the Oxford/AstraZeneca vaccine says the second dose should be administered between 4 and 12 weeks after the first dose.

Last week Pfizer warned that its vaccine's safety and efficacy had not been evaluated on any dosing schedule other than 21 days between jabs, adding that 'there are no data to demonstrate that protection after the first dose is sustained after 21 days'.

However, the JCVI highlighted that another vaccine being developed by Moderna, which like the Pfizer vaccine is based on mRNA technology, has data to support high efficacy up to 108 days after the first dose.

The JCVI said: 'There is currently no strong evidence to expect that the immune response from the Pfizer-BioNTech vaccine would differ substantially from the AstraZeneca and Moderna vaccines.'

Doctors' concerns

Some doctors have expressed concerns about the new approach. The Doctors Association UK (DAUK) has written to the CMOs, the UK health secretaries and the JCVI highlighting the lack of evidence for the Pfizer vaccine schedule change and warning of 'potential severe' medico-legal consequences for clinicians if there was a COVID-related adverse outcome because of a delayed second dose.

The DAUK also pointed out that extending the dosing schedule meant that clinicians were 'more likely to face the scenario of mixing vaccines due to supply issues and the number of vaccines ordered'. Current advice in the Green Book is that people should ideally receive the same vaccine for their second dose, although a different jab can be administered if the first vaccine is unavailable.

There are currently trials underway in the UK looking at mixing vaccines; however, the DAUK said at present there was no data to support this approach.

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