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Vaccination supply dips but effectiveness data provide cheer

Vaccination supply

Costanza Pearce looks at the latest victories and hurdles in the Covid-19 vaccination programme

On the face of it, March seemed to provide the first major setbacks since the start of the vaccination programme. But while supply issues dominate, there was encouraging news around effectiveness in the real world, and transmission rates.

Supply delay

After months of high Covid vaccination rates in the UK – with a doubling of activity in mid-March as supplies increased – the number of jabs will now be restricted this month.

The slowdown stems from ‘a significant reduction in weekly supply’, which GPs were warned about in a letter from NHS England on 17 March.

The letter said mass vaccination centres and community pharmacy-led services should close unfilled Covid vaccine bookings from 29 March and book no further appointments from 1-30 April. However, GPs were told to continue to book patients on the priority list into GP-led vaccination sites – for first and second doses.

Health secretary Matt Hancock later clarified the situation, suggesting the supply shortages would not stop second doses from going ahead. He told the House of Commons on 18 March:

‘There will be no weeks in April with no first doses. There will be no cancelled appointments as a result of supply issues. Second doses will go ahead as planned.’

He confirmed the issue was partly due to a four-week delay in the delivery of five million doses of the Oxford/AstraZeneca vaccine from India – alongside the re-testing of another 1.7 million-dose vaccine batch.

Since mid-February, GPs have been focusing on patients in priority group six – people aged 16 to 64 years with underlying health conditions. By mid-March, NHS England had started inviting all over-50s to book jabs. This marked the final stage of the first phase of the rollout, which aimed to protect those most at risk by ensuring they have at least a first dose by 15 April.

Vaccine proving effective

Despite what Mr Hancock described as a ‘lumpy’ supply, the vaccination programme is proving a success.

The vaccine has now been proven to work well at stopping people from becoming ill. Early results from the first real-world study of the UK vaccine programme – which so far includes the Pfizer/BioNTech vaccine as well as the Oxford one – found ‘a single dose of either vaccine provides significant protection against Covid-19’.

Published as an early pre-print study last month, Public Health England’s review backed up preliminary trial results that said both vaccines would be highly effective against coronavirus.

PHE head of immunisation Dr Mary Ramsay said: ‘We’re increasingly confident vaccines are making a real difference.’

PHE’s analysis, based on 156,930 people, even suggests the vaccines could be more effective than the trials suggested, at least after one dose,  although the data are based on over-70s only.

Pfizer’s phase-three trials, published in November, reported 52% efficacy from 12 days after the first dose. The real-world data show 70% effectiveness for a single dose after 28 days – which is especially encouraging after the UK adopted the policy of administering the second dose after 12 weeks, and not the three weeks measured in the trials.

In terms of second doses, the Pfizer trial showed 95% efficacy seven days after second dose. But the real-world data show a slight drop – to 89% efficacy 14 days after the two-dose course was completed. This is based on the difference in dose intervals, however.

The Oxford vaccine trials reported a 64% efficacy for the first dose  – from 21 days after – while real-world data shows 73% effectiveness from 35 days after the first dose. Rollout in the UK started almost a month after the first Pfizer jabs, so no real-world data on second doses are yet available.

PHE study author Jamie Lopez Bernal tells Pulse: ‘Prior to this, there was very limited data on how effective a single dose of the vaccine was and there was a lot of concern about using this prolonged schedule. But what we are showing is that even a single dose of the vaccine is effective against symptomatic disease, and in particular against hospitalisation and death.’

The team used routine symptomatic testing data to estimate how well the vaccines prevent disease by comparing vaccination rates in those who tested positive with those who tested negative.

With the vaccines reducing the risk of symptomatic disease by around 70%, this translates to around three in 1,000 vaccinated people becoming a symptomatic case, compared with 10 in 1,000 without vaccination, he explains.

Reduced transmission

Health officials have previously cautioned that there was a lack of evidence about whether the jabs stop people passing the virus on.

But now there is an indication the vaccines do stop transmission, based on real-world data. Public Health Scotland reviewed 300,000 health records and found the chance of healthcare workers passing Covid onto others reduced by at least 30% after one vaccine dose.

Researchers looked at people who lived with vaccinated and unvaccinated healthcare workers between 8 December and 3 March to find how many tested positive for Covid-19 or were hospitalised.

The study, which has yet to be peer-reviewed, concluded that after a second vaccine dose, healthcare staff were 54% less likely to pass on the virus.

Dr Diane Stockton, Public Health Scotland lead for the Covid-19 Vaccination Surveillance Programme, said: ‘These results are very encouraging because they suggest the vaccine helps prevent people passing on the virus.’

But she warned: ‘It is important to remember that infection prevention and control practices in healthcare settings remain of paramount importance, as do the mitigations to prevent spread in our daily lives. The risk of transmission did not go down to zero.’

Blood-clotting scares

Last month, GPs reported patients cancelling bookings after some European countries suspended use of the Oxford vaccine over fears around blood clotting.

After a safety review, the European Medicines Agency concluded on 18 March: ‘The vaccine is not associated with an increase in the overall risk of blood clots in those who receive it.’

It added: ‘The benefits of the vaccine in combating the still widespread threat of Covid-19 (which itself results in clotting problems and may be fatal) continue to outweigh the risk of side effects.’

The vaccine may be associated with ‘very rare’ cases of blood clots associated with thrombocytopenia, the EMA said. It stressed it had only reviewed seven cases of blood clots in multiple blood vessels and 18 cases of cerebral venous sinus thrombosis out of 20 million people in the UK and Europe who had received the Oxford vaccine.

As a ‘precautionary measure’, the UK’s MHRA has issued guidance saying patients with a headache lasting more than four days after their Covid vaccination should ‘seek medical attention’ to help rule out thrombosis.