Are Covid-10 vaccines safe for pregnant women?

New Zealand’s Covid-19 vaccination programme began on February 20, 2021 with people working in border-related jobs and their families being the first to be offered the jabs. [1]  At this stage the only Covid-19 vaccine available in NZ is the Pfizer/BioNTech  mRNA vaccine (“COMIRNATY”) and due to the short shelf life of this product once it is out of the deep freeze, some health professionals are also being offered shots in order to to use up defrosted batches before it has to be discarded. [2]

Some of the women in the occupations that have been targeted for early vaccination will be pregnant or considering starting a family, so a specific discussion what is known (and not known) about the effects of Covid-10 vaccines on fertility and pregnancy seems timely.

UK health professionals advised to rule out pregnancy prior to vaccinating women with COMIRNATY

When the Pfizer/BioNTech mRNA vaccine COMIRNATY was “authorisation for temporary supply” and a mass vaccination campaign began in the UK, the advice to health professionals was that a negative pregnancy test was a prerequisite prior to vaccinating women and that women should be advised to avoid pregnancy for at least two months following vaccination.

A document (last updated on December 11, 2020) on the website of the MHRA (Britain’s prescription medicines and healthcare products regulator) stated in relation to the Pfizer/BioNTech mRNA vaccine:

“The data to support safety in pregnancy are insufficient. Therefore, BNT162b2 is not recommended during pregnancy. However, use in women of childbearing potential can be supported provided healthcare professionals are advised to rule out known or suspected pregnancy prior to vaccination. As a precautionary measure, women of childbearing potential are advised to avoid becoming pregnant until at least 2 months after vaccination.” [3]

“In the context of supply under Regulation 174, it is considered that sufficient reassurance of safe use of the vaccine in pregnant women cannot be provided at the present time: however, use in women of childbearing potential could be supported provided healthcare professionals are advised to rule out known or suspected pregnancy prior to vaccination. Women who are breastfeeding should also not be vaccinated.” [4]

What is the reason for the recommendation that breastfeeding women not be vaccinated?

“It is unknown whether BNT162b2 is excreted in breast milk. Therefore, it is recommended that BNT162b2 should not be administered to women who are breastfeeding. Information for Healthcare Professionals and the Information for UK recipients reflect these recommendations. Use in pregnancy and lactation is included as missing information in the RMP [Risk Management Plan]. Use in pregnancy will be investigated as part of the pharmacovigilance plan.” [5]

New advice to health professionals on COMIRNATY and pregnancy

Fast forward to February 2021 and the specific link to “REG 174 INFORMATION FOR UK HEALTHCARE PROFESSIONALS” [6] has revised text (as of 26 January 2021) and no longer states that a test is necessary to rule out pregnancy prior to vaccination.

Instead it states: “Administration of the COVID-19 mRNA Vaccine BNT162b2 in pregnancy should only be considered when the potential benefits outweigh any potential risks for the mother and foetus.”

This is the same phrase used in the NZ datasheet for COMIRNATY on Medsafe’s website.  (A comprehensive analysis of the shortcomings of the datasheet for “COMIRNATY” and information about the potential risks of the vaccine that are omitted from the datasheet may be read at this link: If you are considering this vaccine for yourself (or your patients) please take the time to read the above article which is referenced and followed by additional notes that discuss possible mechanisms for some of the adverse events that have been reported.)

As of late January 2021, COMIRNATY had been available in a few countries for no more than six or seven weeks.  (Its use in the UK began on December 8, for example.) 

So what has changed in a few short weeks that caused the UK regulator to change its stance on the use of COMIRNATY in pregnancy so significantly?

In a single word:  Rats.

Some data from a study of rats vaccinated with COMIRNATY was apparently made available to regulators and on the basis of results reported about an unspecified number of vaccinated rats, they decided that pregnant women could also be vaccinated with COMIRNATY.

The NZ datasheet for COMIRNATY [7] states that the rats in the study were administered four doses of the vaccine over the period of 21 days before mating and up until 20 days of gestation.  The datasheet states that the rats were followed up until their offspring were 21 days old.  Antibodies (to SARS-CoV-2, the virus that causes Coivd-19) were present in both the mother rats, the rat foetuses and the baby rats.  In relation to this research, the datasheet includes this curiously worded sentence: “There were no vaccine related effects on female fertility and pregnancy rate.” [Emphasis added.]  

The datasheet further states: “Animal studies do not indicate direct or indirect harmful effects with respect to pregnancy, embryo/fetal development, parturition or post-natal development.”

There is no study number cited with the brief description of these animal studies in the NZ datasheet so it appears that the animal fertility/reproductive toxicity studies may have been purely in-house research that has not been peer reviewed. 

So what can we learn from this very scanty reporting on the rat study?

  1.  One significant finding is that antibodies were found in foetal rats.

This is an interesting finding because it opens up an important question, which is:

What was the source of the antibodies that were found in the foetal rats?

Were these antibodies generated in the pregnant rats and then crossed the placenta and made their way into the rat foetuses?

Or were the antibodies that were found in the foetal rats produced by the rat foetuses themselves?

In this latter case, the only ways that the foetal rats could produce antibodies to the spike protein for SARS-CoV-2 would be if …

…the spike protein generated in the pregnant mother rats after they had been vaccinated crossed the placenta and stimulated the foetal rats to produce antibodies…


…the synthetic mRNA in COMIRNATY that codes for the spike protein for SARS-CoV-2 crossed the placenta and forced cells in the rat foetuses to produce the spike protein which then stimulated the formation of antibodies in the foetal rats…

It’s not possible to know from reading the datasheet which of the above scenarios may have resulted in antibodies being present in the foetal rats.  However, if the foetal rats were generating antibodies themselves (due to either the spike protein for SARS-CoV-2 and/or the synthetic mRNA that codes for this protein crossing the placenta) this has implications for the health of human babies whose mothers are vaccinated in pregnancy.

How could foetal exposure to the spike protein for SARS-CoV-2 or synthetic mRNA that codes for spike protein for SARS-CoV-2 impact on the health of babies of mothers who are vaccinated in pregnancy?

Research into SARS-CoV-2 suggests several avenues by which vaccination against SARS-CoV-2  during pregnancy might harm the developing embryo/foetus.

  1. There is evidence that suggests the spike protein can cross the blood brain barrier [8] and has caused damage to the brain in some adults who have Covid-19 [9]. (NB: The spike protein alone can cause damage to endothelial cells that form the inner lining of blood vessels – it is not necessary for the whole virus to be present.) If the spike protein can damage an adult brain, any spike protein that is present in a developing foetus could presumably also harm his or her rapidly developing brain.
  2. There is potential for the spike protein to cause damage to the cardiovascular system, liver and kidneys (as well as the brain) as the tiny blood vessels in all of these organs contain high numbers of ACE2 receptors. [10] Therefore, if the spike protein passes through the placenta into the embryo/foetuses (or is generated in the developing foetus if the mRNA passes through the placenta), this might adversely affect the development of other vital organs such as the heart, liver or kidneys.
  3. If the synthetic mRNA makes it through the placenta into the foetal circulation there is a possible risk of the synthetic mRNA becoming incorporated into the rapidly dividing foetal tissues.  The two articles below discuss the mechanisms by which mRNA may be incorporated into nuclear DNA: 

Is there any evidence of adverse outcomes in pregnant women who have been vaccinated with mRNA Covid-19 vaccines?

In a word, sadly, yes. Health professionals and pregnant women are beginning to report pregnancy complications, miscarriage or stillbirth following Covid-19 vaccination.

The link below discusses some of the cases of adverse events in pregnancy including  miscarriage/stillbirth that have been reported to the US VAERS vaccine adverse events system after Covid-19 vaccination.  They do not make happy reading. 

In one case, a woman who had an ultrasound showing a healthy placenta at 28 weeks just prior to vaccination (with the Moderna mRNA Covid-19 vaccine) reports that she was found to have a prematurely aged and calcified placenta only a week later. (Hers was a comparatively happy outcome as she was in hospital having her health carefully monitored and her baby was alive at the time of the report. )

Another link that reports on cases of miscarriage/stillbirth that have been reported to the US VAERS reporting system after Covid-19 vaccination is below:

NB: At the reference above it is possible to go to the VAERS site and read the VAERS entry for each case by clicking on the VAERS reference number which is in blue.  (There may be some overlap on the cases reported between the two links.)

Please note that reports of adverse events can be made to VAERS before there is formal ascertainment that a vaccine was a cause of the adverse health outcome.

Government policy

In the USA, health officials are apparently advocating for pregnant women to be vaccinated against Covid-19 [11]  even though the FDA has given the Moderna and Pfizer/BioNTech mRNA Covid-19 vaccines emergency use authorisation only. (This is an acknowledgement by that agency that these vaccines are experimental.)

Let’s hope that the NZ public health authorities take a more responsible stance and do not try to push pregnant women (or anyone else, for that matter) into accepting any experimental Covid-19 vaccines.

Given the possible risks from being vaccinated during pregnancy is it a better idea to be vaccinated prior to trying for a baby?

This is a good question.  Probably no one knows the answer yet because the mRNA vaccines are so new to the market.  In fact, they are so new that a major clinical trial of COMIRNATY has not yet been completed (and the trial did not enrol pregnant or breastfeeding women as volunteers). [12]

Concern was raised in December 2020 that Covid-19 vaccination might have an adverse effect on female fertility by resulting in the formation of antibodies that target a protein called syncytin-1.  Syncytin-1 is necessary for the formation of the placenta so if this protein were targeted by maternal antibodies, the placenta would not develop and the pregnancy would miscarry.

An article outlining the concerns of Michael Yeadon, PhD and a German medical doctor  Wolfgang Wodarg may be read at this link:

A PDF of the petition that Drs. Yeadon and Wodarg sent to the European Medicines Agency (which also included its authors’ concerns that the vaccine could cause severe allergic reactions due to PEG being included in its formulation) may be downloaded from the link below:


In relation to whether there may be any male fertility concerns in relation to vaccination with Covid-19 vaccines, a study to evaluate possible effects on the fertility (sperm concentration and motility) of vaccinated men began in mid-December 2020. This study is not expected to be completed until June 2021. See:

(It is not clear from the information above whether the study will examine only the Pfizer/BioNTech mRNA vaccine or whether men vaccinated with the Moderna mRNA vaccine will also be recruited for the trial.)

Website editor’s note:  This short article is not intended to be the last word on whether or not vaccination against Covid-19 in pregnancy (or prior to pregnancy) is either safe or desirable.  Nor should this article (or any other articles relating to any health-related topic on this website) be mistaken for medical advice.  Please consult a qualified health professional in relation to your health.

Ed note: References for this article may be found further down this page.

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[3] Pages 49-50 of the British MHRA’sPublic Assessment Report Authorisation for Temporary Supply Public Assessment Report Authorisation for Temporary Supply COVID-19 mRNA Vaccine BNT162b2 (BNT162b2 RNA) concentrate for solution for injection” (henceforth to be abbreviated as the “Public Assessment Report”). (Version that was last updated 11 December 2020)

[4] Pages 49-50 of the British MHRA’sPublic Assessment Report Authorisation for Temporary Supply Public Assessment Report Authorisation for Temporary Supply COVID-19 mRNA Vaccine BNT162b2 (BNT162b2 RNA) concentrate for solution for injection” (henceforth to be abbreviated as the “Public Assessment Report”). (Version that was last updated 11 December 2020)

[5] Page 44 of the British MHRA’sPublic Assessment Report Authorisation for Temporary Supply Public Assessment Report Authorisation for Temporary Supply COVID-19 mRNA Vaccine BNT162b2 (BNT162b2 RNA) concentrate for solution for injection” (henceforth to be abbreviated as the “Public Assessment Report”). (Version that was last updated 11 December 2020)


[7] [7]