More than 600 pregnant women will be recruited in Shropshire and a dozen other areas of the country as part of the new study which will look at what is the optimum time to leave between the first and second doses.
Following 130,000 pregnant women being vaccinated in the US and no safety concerns being raised, the Pfizer and Moderna vaccines were recommended by the independent experts at the Joint Committee on Vaccination and Immunisation for pregnant women in the UK.
Almost 52,000 pregnant women in England have now been vaccinated – similarly, with no safety concerns reported.
Data published last week by NHS England and the University of Oxford also shows no pregnant women who have had both doses of a vaccine have been admitted to hospital with Covid-19.
Only three have been admitted after having their first dose, meaning 98 per cent of those admitted to hospital have not received a jab.
The Preg-CoV study, backed by £7.5 million of government funding and led by St George’s, University of London, will provide vital clinical trial data on the immune response to vaccination at different dose intervals – either four to six weeks or eight to 12 weeks.
This data will help determine the best dosage interval and help to understand about how the vaccine works to protect pregnant mothers and their babies against Covid-19.
Minister for Covid-19 vaccine deployment Nadhim Zahawi said: "Pregnant women are more likely to get seriously ill from Covid-19 and we know that vaccines are safe for them and make a huge difference – in fact no pregnant woman with two jabs has required hospitalisation with Covid-19.
"This government-backed trial will provide more data about how we can best protect pregnant women and their babies, and we can use this evidence to inform future vaccination programmes.
"I encourage anyone who is pregnant and eligible to sign-up and contribute to research that will save lives for years to come."
The trial will involve over 600 pregnant women being vaccinated with either the Pfizer or the Moderna vaccine.
They will be closely monitored by health professionals throughout their pregnancy and following the birth.
Participants will need to be between 18 and 44-years-old, have no health conditions and be between 13 and 34 weeks pregnant on the day of vaccination.
They will receive two doses of a vaccine – or one dose if they’ve already had their first – at either the shorter interval of four to six weeks, or the longer interval of eight to 12 weeks.
They will be scheduled to attend nine visits in total and will be required to complete an electronic diary between visits on any symptoms.
They will also be given a 24-hour mobile number so they can contact one of the trial team at any time if they have concerns.
The scientists behind the trial will analyse blood samples from the participants and one blood sample from their newborn babies, alongside samples from breast milk.
They will use the samples to help understand more about how the vaccines are protecting these individuals from Covid-19, with initial results expected by the end of the year.
The study is open for applications from volunteers, with vaccinations set to start from mid-August.
The trial will be run across 13 National Institute for Health Research sites in England, including Princess Royal Hospital in Telford.
Volunteers can sign up at vaccine.ac.uk/research/preg-cov-trial