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Study Will Test Different Time Intervals for COVID-19 Vaccines in Pregnant Individuals

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Study Will Test Different Time Intervals for COVID-19 Vaccines in Pregnant Individuals

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A new UK-based clinical trial will test the most appropriate time interval between two doses of an mRNA COVID-19 vaccine in pregnant individuals. 

COVID-19 vaccines and pregnancy


In 2020, clinical trials of COVID-19 vaccines now authorized for human use did not include pregnant or breastfeeding individuals. This approach is typical for the clinical study of a new investigational medicinal product and is enforced by regulatory bodies such as the US Food and Drug Administration (FDA) to protect both mothers and pregnancies.

As the global rollout of several COVID-19 vaccines commenced, many pregnant individuals opted to be immunized against SARS-CoV-2 regardless. This enabled scientists to gather real-world retrospective data on the safety and efficacy of the different types of vaccines in this population. Based on the growing data supply, in April, the UK's Joint Committee on Vaccination and Immunisation (JCVI) advised that pregnant persons in the UK should be offered two doses of mRNA-based vaccines (Pfizer–BioNTech's BNT162b2 or Moderna's mRNA-1273) where available.

However, data gaps remain,  Professor of Pediatric Infectious Diseases Paul Heath from St George's University of London explained in a recent press release: "Tens of thousands of pregnant women have now been vaccinated in both the US and the UK with no safety concerns reported, but we still lack robust, prospective clinical trial data on COVID-19 vaccines in pregnant women."

More information is required to determine the best time schedule for administering the two mRNA COVID-19 vaccine doses in pregnant individuals in order to achieve the optimum immune response. A new study led by Heath – known as Preg-Cov – will provide this vital clinical information.

Vaccine dose intervals in pregnancy


Preg-Cov will recruit over 600 low-risk pregnant women aged 18-45-years-old across a number of sites in the UK. All participants will receive two doses of an mRNA-based COVID-19 vaccine (either Pfizer–BioNTech's BNT162b2 or Moderna's mRNA-1273). The eligibility criteria permits the inclusion of individuals that have received their first dose prior to enrolling in the trial. Speaking to Technology Networks, Heath said: "All will be blinded to the COVID-19 vaccine they receive except for the group that have received a dose before pregnancy – as they obviously know what they had already."

Participants must be between 13 and 34 weeks pregnant on the date of the first COVID-19 vaccination, and will be divided into two groups: short interval and long interval dosing. The short interval group will receive their second COVID-19 vaccine between four to six weeks after their first dose, whereas the long interval group will receive their second dose between 8 and 12 weeks after their first. Consequently, some individuals will receive their second dose after delivering their baby. The study will follow all recruits for a period of one year.

"It's important to highlight that all participants in this study will receive a COVID-19 vaccine. This is particularly important with the rising number of cases, the easing of restrictions and low vaccine uptake among pregnant women," Professor Asma Khalil, lead obstetrician for the trial said.

Throughout the duration of the trial, various data will be collected. Recruits will be asked to maintain a symptom diary and blood samples will be obtained from the mother. In some instances, cord blood will also be extracted. "The blood samples are taken from all mothers but cord blood only from mothers at certain sites. This is because we don’t actually need to take as many samples to address the question about transfer of antibody from mother to baby in the cord blood," Heath told Technology Networks.

The trial – which is now open for enrollment – is supported by £7.5 million worth of funding from the UK government. "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," said the Minister for Covid-19 Vaccine Deployment, Nadhim Zahawi. "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."

Professor Paul Heath was speaking to Molly Campbell, Science Writer for Technology Networks. 

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Molly Campbell
Molly Campbell
Science Writer
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