UK Announces World’s First Trial of Switching COVID-19 Vaccines Between Doses

February 4, 2021 Updated: February 4, 2021

The UK government has announced the world’s first clinical trial of switching between different COVID-19 vaccines for the first and second doses.

Scientists are hoping that the trial—which won’t yield initial results until the summer—will reveal how vaccines could be used more flexibly, potentially resolving logistical and supply challenges.

“It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer; unless this is evaluated in a clinical trial we just won’t know,” said UK Deputy Chief Medical Officer professor Jonathan Van-Tam, who is also overseeing the study.

The government emphasised that the current UK vaccine rollout, in which patients take only one vaccine—either Pfizer/BioNTech or Oxford/AstraZeneca—for both doses will not change.

Minister for COVID-19 Vaccine Deployment Nadhim Zahawi said, “Nothing will be approved for use more widely than the study, or as part of our vaccine deployment programme, until researchers and the regulator are absolutely confident the approach is safe and effective.”

The study, involving an expected 800 people, will last 13 months, with initial findings planned to be released in the summer. It will look at various combinations of the Pfizer/BioNTech and Oxford/AstraZeneca vaccines at doses either one month or three months apart.

With the exception of a handful of very small nations, the UK has vaccinated a higher percentage of its population than any other country.

However, vaccine rollout has coincided with the appearance of a more transmissible variant that sparked a second wave of the pandemic and brought with it the highest official COVID-19 death rates in the world.

That UK variant can still be tackled by current vaccines, according to research, although it is a little more resistant.

Another variant from South Africa is thought to be even more resistant to vaccines, although health officials stress that current vaccines still offer protection against it.

The emergence of community transmission cases of that South African variant in various places in England sparked the rollout of localised surge testing earlier this week.

Meanwhile, a spin-off mutation of the UK variant has emerged with the same potentially vaccine-hindering protein structure as the South African and Brazilian variants, according to English health officials.

Public Health England on Feb. 1 reported (pdf) that sample testing has revealed that a key mutation in the South African and Brazilian variants, called E484K, was found in a “limited number” of cases in England.

Out of a total sample of 214,159 cases, analysed on Jan. 26, only 11 were identified as the UK variant with the E484K change.

Despite the low numbers, scientists say that the development is concerning.

On Wednesday, AstraZeneca and the University of Oxford said that they aim to update their vaccine to address the different CCP (Chinese Communist Party) virus variants by the autumn.

The UK has been a world-leader in genomic sequencing of the CCP virus, meaning that it may be picking up on changes occurring globally rather than revealing phenomena unique to the UK.

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