What do we know about the AstraZeneca vaccine in pregnancy?

We have been asked lots of questions on WhatsApp regarding the use of the AstraZeneca Covid-19 vaccine in pregnancy. Here we answer a collection of the queries. 

We have written lots more about the AstraZeneca vaccine, and the other Covid-19 vaccines in pregnancy here. 

Why are other vaccines recommended over the AstraZeneca vaccine in pregnancy?

The Joint Committee on Vaccination and Immunisation (JCVI) told Full Fact that its decision to advise pregnant women in the UK to get the Pfizer-BioNTech or Moderna vaccines was based on “extensive experience of their use in pregnancy” in other countries, especially the US. It added “There is no evidence to suggest that other vaccines, such as AstraZeneca, are unsafe for pregnant women”. 

The JCVI also advises that adults under the age of 40 should be offered an alternative to the AstraZeneca vaccine. This is because of the balance of benefits in terms of avoiding serious Covid-19 illness and the small risk of blood clots with low platelets associated with the vaccine. 

Why are pregnant people still recommended to have a second dose of AstraZeneca vaccine?

Questions that we’ve received on this topic focus on the fact that while Moderna and Pfizer are the vaccines recommended for pregnant women, if someone has already received a first dose of the AstraZeneca vaccine they are still recommended to get the second while pregnant.

We put the question to Public Health England (PHE), which told us that mixing of doses of the vaccine between different brands is not currently recommended. The PHE Green Book, which provides health professionals with the latest information on vaccinations, states that “Individuals who experience severe expected reactions after a first dose of AstraZeneca or Pfizer vaccines appear to have a higher rate of such reactions when they receive a second dose of the alternate vaccine”. This also references a study comparing side effects associated with mix and matching of the two vaccines against giving two doses of the same vaccine.

The Green Book advises that people who have received a first dose of the AstraZeneca vaccine should have a second dose with the same vaccine. The exception to this are people who experienced anaphylaxis or blood clots associated with low platelets following their first dose. 

The JCVI also shared a letter from the Expert Haematology Panel, a group of specialists who have been providing advice to healthcare professionals, which states that there is no evidence that people with a prior history of, or risk factors for blood clots, are more likely to develop the blood clots with low platelets that have been reported after the AstraZeneca vaccine. PHE told us that things like pregnancy and contraception are not likely to increase the risk of this type of complication. 

In addition, the JCVI told Full Fact “there have been no safety concerns identified for thrombosis/thrombocytopenia associated with the second dose of the AstraZeneca vaccine”. 

The MHRA and Royal College of Obstetricians & Gynaecologists have both noted that there have been very rare reports of this type of reaction following a second dose of AstraZeneca, however the MHRA says that there is “no evidence of an association of this syndrome with the second dose of AZ vaccine”. A study published in the Lancet in August reviewing 220 of the first cases in the UK also found that individuals were affected after a first dose only. 

What studies have contributed to the JCVI decision to use the AstraZeneca vaccine in pregnancy? 

Full Fact asked the JCVI about the evidence behind its decision on recommending a second AstraZeneca vaccine dose during pregnancy. 

It pointed us towards developmental and reproductivity testing of the AstraZeneca vaccine in animals, which has not raised any safety concerns in these areas and another study from St George’s University that included 13 pregnant women who received the AstraZeneca vaccine. It also noted that other adenovirus vector vaccines such as the Ebola vaccine have been widely used without safety concerns.

The JCVI added that monitoring of all vaccinated individuals is ongoing through the MHRA Yellow Card Scheme. 

The information included in this article contains the latest evidence and official guidance available at the time it was written. This is not a substitute for medical advice. If you require specific medical advice please consult your GP or midwife.