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The University of Southampton

New study into COVID-19 vaccine dose interval for pregnant women launches in Southampton

Published: 5 August 2021
Baby Bump

The country’s largest clinical study investigating the best gap between first and second COVID-19 vaccine doses for pregnant women is launching in Southampton.

The Preg-CoV study, which will take place in the NIHR Southampton Clinical Research Facility (CRF) at University Hospital Southampton NHS Foundation Trust, will begin recruiting participants later this month. Dr Chrissie Jones, Associate Professor in Paediatric Infectious Diseases at University of Southampton, will be the local investigator for the trial. 

Led by St George’s, University of London, and backed by £7.5 million of government funding, the study will provide vital clinical trial data on the immune response to vaccination at different dose intervals. This will help determine the best dosage interval and tell us more about how the vaccine works to protect pregnant mothers and their babies against COVID-19.

Participants will receive two doses of either the Pfizer/BioNTech or the Moderna vaccines (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. More than 600 pregnant women will take part in the study across 13 NIHR-supported sites.

Participants will need to be between 18 and 44-years-old, generally healthy and between 13 and 34 weeks pregnant on the day of vaccination. Participants will be closely monitored by health professionals throughout their pregnancy and following the birth, with the safety of the women taking part in the study the utmost priority.

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.

Pregnant women are more likely to develop severe COVID-19 or die from the disease, but are excluded from clinical trials with new vaccines. This means there is currently very limited clinical trial data on the immune response and side effects caused by the vaccines for these women.

Following 130,000 pregnant women being vaccinated in the US and no safety concerns being raised, the Pfizer/BioNTech and Moderna vaccines were recommended by the independent experts at the Joint Committee on Vaccination and Immunisation (JCVI) for pregnant women in the UK. Over 52,000 pregnant women in England have now been vaccinated - similarly, with no safety concerns.

Recent data published last week by NHS England and the University of Oxford 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 99% of those admitted to hospital have not received a jab.

The scientists behind the trial will analyse blood samples from the participants and one blood sample from their newborn babies, alongside samples from breastmilk. They will use the samples to help understand more about how the vaccines are protecting both pregnant women and potentially also their babies from COVID-19, with initial results expected by the end of the year.

Those interested in finding out more and taking part can visit the study’s website:

Participants will also be recruited to the study by invites sent through the NHS COVID-19 Vaccine Research Registry, which allows research teams to speak to suitable volunteers who have signed up to be contacted about taking part in vaccine studies.

Dr Chrissie Jones said:

"While we have a large amount of real-world data which tells us that it's safe for pregnant women to receive approved COVID-19 vaccines, the data gathered from a clinical trial like this will give us additional information about how these approved vaccines can be used in pregnancy to ensure optimal protection for the mother and baby.

“All women taking part in the study will receive the approved Pfizer/BioNTech or Moderna vaccines, as well as additional monitoring and support from their local research team."

Dr Matthew Coleman, Consultant Obstetric Physician at University Hospital Southampton, added:

“Current experience strongly suggests that COVID-19 vaccination in pregnancy is the safest choice in reducing the risk of occasionally serious COVID-19 illness for mothers and early birth for babies. However, more research is required to understand how COVID-19 vaccination achieves this, including the best timing for vaccination.

“Pregnant women, especially later in pregnancy, seem to be at additional risk from more serious COVID-19 illness, so this study is important for women as individuals and for the wider community, including other pregnant women and their families.”

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.”

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