Explainer on COVID vaccination, fertility, pregnancy and breastfeeding

Viki Male, Associate Professor in Reproductive Immunology at Imperial College London

v.male@imperial.ac.uk

@VikiLovesFACS 

Last updated 5 September 2025

1. I heard that the COVID vaccine might reduce female fertility. Is this true?

No. Multiple strands of evidence tell us that COVID vaccines do not harm female fertility.

Pregnant participants were not included in the first round of clinical trials of the COVID vaccines, and participants were asked to avoid becoming pregnant. Nonetheless a number of people became pregnant by accident. The accidental pregnancies occurred equally across the vaccinated and unvaccinated groups, which tells us that vaccines did not prevent pregnancy.

* Note that these pregnancy losses potentially include terminations reported as miscarriages, because the participant lives in a country in which termination of pregnancy is illegal. If the data from these countries is excluded, the pregnancy loss rate is 21% with the control and 14% with the vaccine.

Following the general rollout, we have collected further data about the effect of the vaccines on fertility. In a cohort of 2,126 couples trying to conceive in the USA and Canada between December 2020 and September 2021, vaccination status in the female partner did not change the per cycle rate of conception. In a follow-up study of 1815 of these couples who conceived, vaccination prior to conception did not affect outcomes in early pregnancy. In IVF patients, COVID vaccination does not affect ovarian function, egg quality, fertilisation or clinical pregnancy rate (Aharon, Bentov, Safrai, Morris, Morris again, Orvieto, Odeh-Natour, Avraham, Jacobs, Albeitawi, Aizer and Danielli Miller for mostly mRNA vaccines). Four studies looking at AMH as a measure of ovarian reserve before and after vaccination found that it did not change (Mohr-Sasson, Soysal, Horowitz, Yang). A meta-analysis that synthesises these results found no impact of COVID vaccination on female fertility.

2. I heard that getting the COVID vaccine might cause changes to my period. Is this true?

Yes, but the changes are small and cycles quickly return to normal.

Six studies  (Edelman, Gibson, Alvergne, Edelman again, Wesselink, Alvergne again) which recruited participants before they were vaccinated and asked them to record their cycles in real time found that vaccination was associated with a delay to the next period that was small compared to normal variation (0 - 3.9d, with the largest delay seen in those who received both doses in a single cycle) but that cycle timings returned to normal within one or two months. Another study which recruited participants before they were vaccinated (Darney) found that 4% of people experienced heavier than usual flow in the period after vaccination, with flow returning to normal the following cycle. This is in line with findings from two Norwegian cohorts (18-30 year olds and 12-15 year olds) who were asked to recall their pre and post-vaccine periods. periods and among whom 8% and 3%, respectively, reported heavier than usual flow immediately after vaccination.

A study of the entire female population in Sweden found that people who had been vaccinated against COVID were not more likely to seek medical advice about changes to their cycle, suggesting these changes were largely unconcerning. However, the same study did find a small increase in individuals seeking medical advice about post-menopausal bleeding within 90 days of vaccination.

3. I heard that the COVID vaccine might reduce male fertility. Is this true?

No. Multiple strands of evidence tell us that COVID vaccines do not harm male fertility.

In a cohort of 2,126 couples trying to conceive in the USA and Canada between December 2020 and September 2021, vaccination status in the male partner did not change the rate of conception and seven studies looking at sperm count and quality before and after mRNA COVID vaccination found no concerning changes (Orvieto, Safrai, Reschini, Gonzalez, Lifshitz, Barda, Gat and Danielli Miller). A meta-analysis that synthesises these results found no impact of COVID vaccination on male fertility.

On the other hand, COVID infection can cause inflammation of the testes and temporarily reduces male fertility;  COVID vaccination protects against testicular inflammation.

4. I am pregnant. What are the risks of catching COVID during pregnancy?

There is some evidence that COVID infection increases the risk of miscarriage (Balachandren, Sacinti), although not all studies have found this (Cosma, Freiesleben, Calvert). There is clearer evidence that COVD infection causes preterm birth and stillbirth and babies born to COVID patients are more likely to be admitted to the neonatal unit (summarised here). Babies born to unvaccinated individuals who catch COVID during pregnancy are also more likely to experience respiratory distress. Pregnant COVID patients are more likely to need intensive care than COVID patients who are not pregnant.

5. Does the vaccine prevent people from catching COVID during pregnancy?

Five studies from the pre-omicron era found that the primary course of COVID vaccination is as effective during pregnancy as they are in the general population (Goldshtein, Dagan, Magnus, Butt and Morgan). More recent studies have looked at the effectiveness of boosters against omicron. Schrag found boosters 97% protective against hospitalisation and 81% protective against infection in the delta period, and 86% protective against hospitalisation and 79% protective against infection in the omicron period. Guedalia found boosters 97% effective against hospitalisation and 99% against severe disease in the delta period, and 94% effective against severe disease in the omicron period. Villar found boosters 30% effective against any infection and 76% effective against severe disease in the omicron period, with mRNA vaccines more effective than adenovirus vectored vaccines.

Five studies have looked at how vaccination impacts disease severity in those who catch COVID despite having been vaccinated, finding that even in this population, vaccination is 80-90% protective against moderate or severe disease (Morgan, Ilter, UK ONS, Decenti, Martinez-Varea). There is also some evidence that vaccination reduces the rate of preterm birth and babies suffering respiratory distress in people who catch COVID despite having been vaccinated. No case of COVID stillbirth has been reported in a vaccinated individual.

A meta-analysis synthesising all the evidence on this to January 2023, and looking at mostly mRNA COVID vaccines, found that vaccination in pregnancy reduces the chance of infection by 61% and hospitalisation by 94%.

6. Can the COVID vaccine cross the placenta?

Two studies have looked to see if vaccine mRNA can be found in placenta or cord blood. One study of 19 babies could not find any (Prahl) but a case study of two babies found degraded mRNA in the placenta of two babies and umbilical cord blood of one (Hanna).

A study of 48 placentas collected shortly after vaccination was unable to detect any Spike protein or mRNA. Vaccination is also not associated with any placental pathology (Shanes, Boelig).

To determine whether and vaccine mRNA that crosses the placenta is active (able to produce protein) we look at anti-spike IgM in babies. Four studies looking at a total of 192 babies born following COVID vaccination do not find anti-spike IgM in babies, indicating that they have not been exposed to vaccine protein (Mithal, Beharier, Bashi, Prahl).

7. Is it safe to have the COVID vaccine during pregnancy?

Yes. 221 pregnant participants received mRNA COVID vaccines as part of clinical trials (Pfizer 1, Pfizer 2, Moderna) and these found no evidence of safety concerns in pregnancy. However, because the trials only included small numbers of pregnant participants, more detailed information about safety has been collected during the general rollout.

Passive monitoring schemes, such as Yellow Card in the UK and VAERS in the USA, collect information that doctors, patients and their families report. Neither of these schemes has detected adverse events occurring more often following COVID vaccination than they normally do in pregnancy. You can read Yellow Card reports here. You can find peer-reviewed publications on the safety of COVID-19 vaccination in pregnancy based on VAERS data here (to October 2021) and here (for boosters).

49 studies that actively track the outcomes after COVID vaccination have also been done, across 10 countries and at least 523,429 people vaccinated in pregnancy. You can find a summary of all these studies here. A meta-analysis synthesising all the evidence to January 2023 found vaccination was associated with a reduced risk of hypertensive disorders of pregnancy, C-section and babies being admitted to intensive care, and no increased risk of any adverse outcome in pregnancy, at birth, or in newborns.

Importantly, studies that have followed up babies after birth, for up to twelve months, have found no increased risk of serious illness or death between babies in the vaccinated and unvaccinated groups (Goldshtein, Carlsen, Halasa, Jorgensen, Zerbo, Lipschuetz, Cassidy, Jorgensen again). A study looking at neurodevelopment at 12 and 18 months found no difference between babies in the vaccinated and unvaccinated groups (Jaswa).

8. Will being vaccinated while I am pregnant give my baby any protection against COVID once they are born?

Yes. Although the vaccine itself does not cross the placenta, the protective antibodies made by the body (IgG) do, and this provides some protection for babies after birth (first report, Gray, Mithal, Prabhu, Collier, Beharier, Zdanowski, Rottenstreich, Atyeo, Prahl, Shook, Sajadi, Yang, Matsui, Otero, Cassidy and Murphy).

In the pre-omicron era, vaccination in pregnancy was 61% effective at protecting babies under six months old from hospitalisation with COVID (Halasa, Danino). More recent studies (Carlsen, Halasa again, Jorgensen, Zerbo, Simeone, Guedalia) looking at protection specifically during the omicron era, found two doses of vaccine in pregnancy approximately 30-50% protective against hospitalisation with omicron, and three doses 60-80% protective. Studies looking at protection for babies after a booster in pregnancy compared to two doses only find that the booster dose adds approximately 50% protection, compared to no booster (Lipschuetz, Cardemil). Vaccination also increases protection of infants, even following prior maternal infection (Guedalia).

9. I am breastfeeding. Should I get the vaccine if I am offered it?

Based on Yellow Card data, the MHRA says “There is no current evidence that COVID-19 vaccination while breastfeeding causes any harm to breastfed children or affects the ability to breastfeed.” A study that asked 50 breastfeeding people to document any side effects in themselves or their babies found no severe adverse events.

Six studies have looked for vaccine mRNA in breast milk. Two of these (Golan, Mattar) were unable to detect it, whereas four that first concentrated the mRNA from milk, were able to detect it in some donors at very low levels. Low found mRNA at 2 parts per billion in 3 out of 10 milk donors. You can read an explanation of what 2 parts per billion means here. Yeo found mRNA in 4 out of 31 milk donors at a maximum of 0.17 parts per billion and Hanna found mRNA in 3 out of 11 milk donors at a maximum of 0.011 parts per billion. In a follow-up study Hanna (again) went on to confirm that the trace amounts of mRNA do found in breast milk are not active. A study that looked for the chemical PEG, which is used to stabilise mRNA vaccines, in the breast milk of 13 people did not find that its levels increased after vaccination (Golan).

A number of studies have shown that the protective antibodies your body makes get into breast milk at high concentrations. One of these studies found that antibodies could persist in breast milk for as long as six months after vaccination. There is also some evidence that T cells that respond to COVID19 get into breast milk (Goncalves, Armistead), although it is not clear whether this provides any protection to babies.

Revision history

Updated 24 January 2021 to include a trial-by-trial breakdown of the outcomes for participants who became pregnant during the trials.

Updated on 26 January 2021. Q3. “Following the publication of the data showing that the vaccine is safe in pregnant animals...” changed to “Following the publication of the interim data showing that the vaccine is safe in pregnant animals...” Q5 updated to more closely mirror the language of the JCVI report.

Updated on 3 February 2021 to incorporate developmental and reproductive toxicity studies using the Oxford/AZ vaccine in mice. I have also changed the link on the risks of COVID-19 infection during pregnancy to point to a living systematic review in the BMJ, which acts as a more comprehensive and up-to-date resource than the individual studies.

Updated on 10 February 2021 to add the safety data that has so far been collected in the USA and UK.

Updated on 19 February 2021 to add further safety data collected in the USA and UK.

Updated on 24 February 2021 to add an easy-reference table summarising the accidental pregnancy data.

Updated on 3 March 2021 to add the safety data that has been collected through V-safe in the USA, and to update the data that has been collected through the VAERS and Yellow Card schemes.

Updated on 4 March 2021 to add data about transfer of antibodies across the placenta and through breast milk following vaccination, and to add a link to my article at Nature Reviews Immunology.

Updated on 11 March 2021 to add data about accidental pregnancies in the Janssen vaccine trial, reformat to move the details of the accidental pregnancies to question 2, and new data about the effects of vaccination on antibodies crossing the placenta and into breast milk. I have also updated the VAERS data, to include data collected to 26 February.

Updated on 19 March 2021 to update VAERS data, collected to 11 March.

Updated on 23 March 2021 to add a new study on transfer of antibodies across the placenta, and to update the first preprint that came out on this to its final, published form.

Updated on 29 March 2021 to add a new study about the transfer of antibodies into breast milk and to update VAERS data, collected to 19 March.

Updated on 1 April 2021 to add another study looking at transfer of antibodies across the placenta following vaccination.

Updated on 5 April 2021 to reformat the answer to Question 6 and to add information about the UK’s new active surveillance system.

Updated on 8 April 2021 to add another study showing that antibodies are transferred across the placenta following vaccination.

Updated on 9 April 2021 to update VAERS data, collected to 4 April.

Updated on 13 April 2021 to add another study showing that antibodies are found in breast milk following vaccination

Updated on 18 April 2021 to reflect the new advice in the UK that all pregnant people should be offered the vaccine, and to update VAERS data, collected to 8 April.

Updated on 22 April 2021 to incorporate the updated V-safe data.

Updated on 26 April 2021 to update VAERS data, collected to 16 April

Updated on 5 May 2021 to update VAERS data, collected to 3 May, and to add a new study on the immune properties of breast milk following vaccination.

Updated on 14 May 2021 to add a new study on antibodies crossing the placenta and entering breast milk following vaccination

Updated on 25 May 2021 to add a new study on antibodies crossing the placenta following vaccination

Updated on 28 May 2021 to add data to show that vaccines do not cross the placenta, and further data to show they don’t cross into breast milk. Also added, data to show that they don’t raise antibodies to the placental protein syncytin, and another study into the outcomes for babies whose mothers are vaccinated during the third trimester of pregnancy.

Updated on 2 June 2021 to add a study showing no placental pathology is associated with COVID vaccination.

Updated on 3 June 2021 to add two studies showing no impact of vaccination on fertility in IVF patients.

Updated on 4 June 2021 to add another study showing no impact of vaccination on pregnancy rate in IVF patients.

Updated on 7 June 2021 to update VAERS data, collected to 28 May.

Updated on 30 June 2021 to add a new study looking at antibodies and vaccine mRNA in breastmilk following vaccination

Updated on 13 July 2021 to add a new study on safety and efficacy of the Pfizer vaccine specifically in pregnant people

Updated on 15 July 2021 to add new information on the safety of COVID vaccination in pregnancy, collected in Ontario, Canada.

Updated on 22 July 2021 to add a pregnancy registry study from Israel, and another study showing that antibodies cross the placenta following vaccination

Updated on 26 July 2021 to add UKOSS data on COVID19 hospitalisations during pregnancy, and to reorder and reformat the document as some parts of it were getting out of hand!

Updated on 27 July 2021 to add another study showing no impact of vaccination on fertility in IVF patients, and to add studies about the effect of COVID19 vaccination on sperm quality

Updated on 10 August 2021 to add a new study on the safety of COVID vaccinations in pregnancy from the UK.

Updated on 12 August 2021 to add data from the V-safe datalink, showing that 1073 people who had completed their vaccinations had gone on to report pregnancies to their healthcare providers.

Updated on 13 August 2021 to add the follow-up study done in the V-safe pregnancy registry cohort, plus two new studies on antibodies in breast milk following vaccination

Updated on 18 August 2021 to add a statement from the MHRA on Yellow Card reports of vaccination during pregnancy, to the 16th August

Updated on 26 August 2021 to add another study showing transfer of antibodies into breast milk following vaccination

Updated on 3 September 2021 to add a statement from the MHRA on Yellow Card reports of vaccination in people who are breastfeeding, to the 25th August

Updated on 8 September 2021 to add a second study from Israel on the effectiveness of COVID vaccination specifically in pregnancy

Updated on 9 September 2021 to add a case-control study using Vaccine Safety Datalink data to show no association between miscarriage and COVID vaccination in the previous 28 days.

Updated on 13 September 2021 to reflect a post-publication change to this study. Originally, they estimated miscarriage rates. In the update, they state the absolute numbers without an estimate of rate. Rates are now calculated in a study on the same dataset, with longer follow-up

Updated on 15 September 2021 to cite a review of studies about COVID and male fertility, rather than just one.

Updated on 27 September 2021 to add another study showing transfer of antibodies into breast milk following vaccination - although note that this study found that mRNA vaccines are rather better at doing this than the Janssen vaccine.

Updated on 29 September 2021 to add data from V-safe and Vaccine Safety Datalink presented at the ACIP meeting on September 23rd.

Updated on 14 October 2021 to add a new study showing that antibodies raised by vaccination do not bind the placental protein syncytin-1.

Updated on 22 October 2021 to add a case-control study from Norway showing no association between miscarriage and COVID vaccination in the previous three or five weeks.

Updated on 25 October 2021 to add updated fertility and pregnancy loss data published from the AstraZeneca trials

Updated on 19 November 2021 to add two new studies looking at the transfer of antibodies across the placenta following vaccination in pregnancy

Updated on 25 November 2021 to add new data released by UKHSA on birth outcomes of vaccinated vs unvaccinated people in the UK from January to August 2021

Updated on 30 November 2021 to add an Israeli study looking at outcomes at birth for those vaccinated in pregnancy, compared to those who were not vaccinated

Updated on 6 December 2021 to add a new preprint showing spike-specific T cells in breastmilk, and to update a preprint on the same topic to the paper, now published following peer review.

Updated on 10 December 2021 to add a new preprint showing that vaccination does not lead to the production of anti-Syncytin1 antibodies

Updated on 16 December 2021 to add a new preprint looking at the ability of mRNA COVID vaccines to cross the placenta

Updated on 17 December 2021 to add a new preprint looking at how long maternal anti-COVID IgG lasts in babies after birth

Updated on 22 December 2021 to add an update from the BORNOntario registry showing no difference in the rate of stillbirths between vaccinated and unvaccinated people in Ontario, January - October 2021

Updated on 28 December 2021 to add a new preprint looking at antibodies in babies following vaccination before pregnancy or while breastfeeding and this study on the safety of mRNA vaccination in those who are breastfeeding.

Updated on 5 January 2022 to add recent data from UKOSS and MBRRACE to the section on vaccine effectiveness in pregnancy and to tidy up and reformat the section on vaccine safety in pregnancy (but with no new data).

Updated on 6 January 2022 to add a new cohort study using data from the Vaccine Safety Datalink

Updated on 6 January 2022 to add a new section on COVID vaccination and menstrual changes with links to new studies from the USA and Norway.

Updated on 10 January 2022 to add a study looking at ovarian reserve before and after vaccination in fertile volunteers

Updated on 14 January 2022 to add new data on the safety and effectiveness of COVID vaccines in pregnancy from Scotland

Updated on 21 January 2022 to add a new study looking at conception rates following COVID infection and vaccination

Updated on 24 January 2022 to update from preprints to peer reviewed versions of articles, where these have become available, to update the systematic review on the risks of COVID in pregnancy to this newer one, and to make the links to the studies on transplacental antibody transfer and transfer of antibodies to breast milk easier to navigate

Updated on 28 January 2022 to add a new study on how COVID vaccination affects the success of IVF and to change the link to the UK HSA data to the latest release

Updated on 11 February 2022 to add a new cohort study on vaccination in pregnancy, including six months of post-birth follow-up data

Updated on 15 February 2022 to update from the preprint to the peer-reviewed version of Shook et al

Updated on 16 February 2022 to add the first study looking at how effective vaccination in pregnancy is at protecting newborns from COVID

Updated on 8 March 2022 to fix a broken link

Updated on 10 March 2022 to add V-safe data about post-vaccination pregnancies to June 2021

Updated on 18 March 2022 to add a link to my Nature Reviews Immunology article which is basically a peer-reviewed version of this Explainer (shh! don’t tell the journal!)

Updated on 23 March 2022 to add a new preprint looking at transfer of antibody across the placenta.

Updated on 25 March 2022 to add a new study done using the BORN Ontario registry.

Updated on 1 April 2022 to add this study, which looked for Spike mRNA and protein in placentas after vaccination

Updated on 4 April 2022 to add this study, which looked at rates of congenital abnormalities specifically following vaccination in the first trimester

Updated on 23 April 2022 to add the updated UKHSA data on pregnancy outcomes for vaccinated compared to unvaccinated people in the UK

Updated on 25 April 2022 to update the section on breastfeeding and vaccination. Two preprints looking for vaccine mRNA in milk have been updated to link to their peer-reviewed versions: Golan and Low, and a third study (Yeo) on the same topic has been added. The list of studies on antibodies in breast milk is getting too long to be manageable, so has been replaced with a systematic review. The list of studies replaced by the systematic review is: Gray, Perl, Friedman, Baird, Collier, Charepe, Low, Kelly, Jakuszko, Romero Ramirez, Fox, Sajadi, Golan and Juncker.

Updated on 13 May 2022 to add new data on vaccine coverage from UKHSA, a systematic review and meta-analysis showing that COVID vaccination reduces the rate of stillbirth, and three vaccine safety in pregnancy studies that have come out over the last few months, but I only just spotted (Trostle, Dick, Magnus).

Updated on 16 May 2022 to add two studies that look at effectiveness of COVID vaccination at preventing disease severity in pregnancy: Ilter and  Morgan.

Updated on 22 May 2022 for easier navigability

Updated on 31 May 2022 to add a new cohort study from Boelig and colleagues.

Updated on 1 June 2022 to add new data from the Swiss COVI-PREG registry.

Updated on 6 June 2022 to update a preprint on the lack of anti-syncytin antibodies following COVID-19 vaccination to its peer-reviewed version and to add a new study looking at protection of babies under 4 months old following vaccination in pregnancy

Updated on 9 June 2022 to replace the original December 2020 FDA briefing document for the Pfizer vaccine with the updated data submitted for full approval in August 2021 - more pregnancies and longer follow ups are now shown in the table in q1. You can find the original figures shown in that table here

Updated on 24 June 2022 to include a new study looking at protection of newborns against COVID hospitalisation, following vaccination in pregnancy, and to update the section on sperm count and quality before and after vaccination by adding three more studies (Barda, Lifshitz and Gat).

Updated on 7 July 2022 to add a new preprint on vaccine safety in pregnancy from Australia and to update a preprint on antibody transfer across the placenta following vaccination to the version published following peer review.

Updated on 12 July 2022 to add data from the UK office for national statistics on vaccine effectiveness against hospitalisation in pregnancy, among those who already have a positive COVID test

Updated on 26 July 2022 to add a new preprint from Israel looking at the effectiveness of boosters in pregnancy

Updated on 4 August 2022 to add two new studies on the effects of vaccination on the menstrual cycle (Alvergne and Gibson).  

Updated on 23 August 2022 to add studies on the risk of miscarriage following SARS-CoV2 infection (Balachandren, Sacinti, Cosma and Freiesleben) and on COVID vaccine safety in pregnancy (Fell, Piekos, Sadarangani).

Updated on 25 August 2022 to add studies on IVF outcomes following COVID vaccination (Odeh-Natour, Avraham, Xia).

Updated on 29 August 2022 to point to the latest version of the UKHSA data

Updated on 27 September to add a new study on the levels of vaccine mRNA in breast milk

Updated on 27 September to add a new study on the effectiveness of boosters during pregnancy

Updated on 2 October to add a new study on the effect of COVID vaccination on periods

Updated on 4 October to add a new meta-analysis looking at maternal and neonatal outcomes following COVID vaccination in pregnancy

Updated on 10 October to add a new study looking at the effect of inactivated COVID vaccines on outcomes following frozen embryo transfer.

Updated on 20 October to add the data on safety and effectiveness of COVID vaccines in pregnancy presented at the ACIP meeting. I have also removed some links to population-level data that is now more than a year old (UK intensive care data between February and July 2021 and between May and October 2021).

Updated on 3 November to add a new study looking at the risk of miscarriage or ectopic pregnancy following COVID vaccination in early pregnancy

Updated on 5 November to change a preprint to the version published after peer review

Updated on 15 November to change another preprint to the version published after peer review

Updated on 28 December to add another study on the effect of vaccination on IVF outcomes

Updated on 10 January to add a systematic review and meta-analysis showing no effect of COVID vaccination on male or female fertility. I have also removed the section that keeps a count of how many on-the-record post-vaccination pregnancies there are, as these are now out of date (USA: 27,370 people had reported post-vaccination pregnancies to the CDC by 14 June 2021, 10,178 people in the USA who had had at least one dose of the COVID vaccine had reported a pregnancy to one of the nine largest healthcare providers by 31 July 2021; Ontario: 712 people had reported becoming pregnant after having received two doses of COVID vaccine by June 2021; UK: 20,691 people had received at least one dose of the COVID vaccine prior to pregnancy, become pregnant and given birth by January 2022).

Updated on 13 January 2023 to add a new cohort study on COVID vaccine safety in pregnancy

Updated on 18 January 2023 to add a new study on vaccine effectiveness in the omicron period

Updated on 19 January 2023 to add a vaccine safety in pregnancy study that I missed when it came out last year

Updated on 26 January 2023 to add a new study looking at vaccine effectiveness against moderate or severe disease

Updated 6 February 2023 to add studies on COVID vaccine safety and effectiveness in pregnancy not previously compiled: de Silva, 2022, NEJM; Moro, 2022, Obstet Gynecol; Schwarz, 2022, AJOG; Magnus, 2023, Clin Infect Dis

Updated on 9 February 2023 to add a new study looking at congenital abnormalities following vaccination in pregnancy and a new study on vaccination in pregnancy protecting babies after birth

Updated on 20 February 2023 to add a new preprint looking at pregnancy outcomes after vaccination in Scotland

Updated on 22 February 2023 to add a 2022 vaccine safety study from Romania

Updated on 15 March 2023 to add a new study on vaccination in pregnancy protecting babies after birth

Updated on 24 March 2023 to add another study on protection of infants following vaccination in pregnancy

Updated on 19 April 2023 to add a new prospectively recruited study of menstrual flow following COVID vaccination

Updated on 10 May 2023 to add a fourth study showing no anti-spike IgM in cord blood following COVID vaccination in pregnancy and a new national cohort study from Sweden on people seeking medical advice for menstrual changes post-vaccination

Updated on 19 May 2023 to add studies that are not new but came up in a literature search I had a chance to do today: Peretz-Machluf (vaccine safety in pregnancy), Butt (vaccine effectiveness in pregnancy), Morgan (vaccine effectiveness in pregnancy)

Updated on 20 May 2023 to replace data presented at an ACIP meeting with the analysis published after peer review 

Updated on 21 June 2023 to streamline information about COVID vaccination and fertility. Evidence that antibodies against Spike protein do not cross-react with Syncytin are no longer included in the main body of text, but you can still find them  here, here and here.

Updated on 22 June 2023 to add two new studies on AMH levels before and after COVID vaccination in fertility patients  (Horowitz, Yang).

Updated on 23 June 2023 to add a new study on the risk of congenital abnormalities following COVID vaccination in pregnancy

Updated on 15 July 2023 to add a study that followed up babies born after COVID vaccination in pregnancy until they were 12 months old

Updated on 11 August 2023 to add a new study on antibody crossing the placenta

Updated on 1 September 2023 to add recently-released data from the trial of the Pfizer vaccine specifically in pregnant participants

Updated on 6 September 2023 to check all links still working and update where necessary

Updated on 20 September 2023 to add a study confirming that vaccine mRNA in breast milk is inactive

Updated on 3 October 2023 to add a new study on vaccine effectiveness in pregnancy against hospitalisation of babies

Updated on 10 November 2023 to add a study on vaccine effectiveness against severe COVID in pregnancy

Updated on 15 November 2023 to add a study looking at the effect of COVID vaccination prior to conception on early pregnancy outcomes

Updated on 8 December 2023 to update the total number of observational studies and participants, as given in the linked table

Updated on 17 January 2024 to add a study on the effect of COVID vaccination on menstrual cycle length published last year

Updated on 26 January 2024 to add a study on neurodevelopment of babies born after vaccination in pregnancy and on the effect of vaccination on respiratory distress in babies born following COVID infection in pregnancy and remove information on vaccines used largely in China (Cao, Shi, Huang, Xia, Zhu).

Updated on 7 February 2024 to add a new, large cohort study on neonatal outcomes following COVID vaccination in pregnancy

Updated on 8 February 2024 to add a study that looked for vaccine mRNA in umbilical cord blood

Updated on 16 February 2024 to add a study comparing protection for babies born after a booster dose in pregnancy, compared to two doses only

Updated on 10 April 2024 to add two studies on the effectiveness of COVID vaccination during pregnancy in protecting infants after birth. One new (Guedalia), one new to me (Danino).

Updated on 25 April 2024 to add a new study of pregnancy outcomes following COVID vaccibation in IVF patients

Updated on 23 May 2024 to replace two outdated meta-analyses on the safety and effectiveness (Prasad, Watanabe) of COVID vaccination in pregnancy with a more recent one 

Updated on 4 July 2024 to add a new study looking at vaccination specifically in the first trimester, and major congenital abnormalities

Updated on 26 June 2025 to remove guidance specific to the pandemic eara, and to add two new case-control studies from the Vaccine Safety Datalink, showing no association between COVID vaccination and stillbirth or miscarriage 

Updated on 17 July 2025 to to add a new study from V-safe, showing no increased risk of congenital abnormalities associated with COVID vaccination during the first trimester

Updated on 5 September 2025 to add a new study from the Vaccine safety datalink showing reduced risk of preterm birth and no altered risk of any other condition, associated with COVID vaccination during pregnancy