An interesting preprint published by Bertrand and others in medRxiv evaluated this issue dated April 25th 2021. 

The American College of Obstetrics and Gynaecology and the Society for Maternal Fetal medicine have recommended that the mRNA vaccines produced by Pfizer and Moderna can be made available to lactating women.  

However, initial trials excluded breastfeeding women and this leads to a question about their safety.  

One study of 31 breastfeeding women who received an mRNA vaccine found that greater than 60% reported side effects.  

The researchers tried to evaluate this on a larger sample of vaccinated breastfeeding women and their breast fed children.  

They enrolled breastfeeding women in The US who had received an mRNA vaccine at the University of California.  

Demographics, health history, vaccine brand and maternal symptoms and child events were collected by maternal interview and questionnaire for seven days following each dose.  

Between December 2020 and February 2021, 180 women who had received either of the mRNA vaccines were enrolled in the study.  128, 71.1% received the Pfizer vaccine and 52, 28.9% received the Moderna vaccine.  Child age at enrolment was 7.47 months and the majority, 86% were exclusively breastfed.

Following the first dose, a similar proportion of women reported vaccine symptom by brand, 89.4% in the Pfizer, 98.1% in the Moderna.  

Frequency by specific symptom did not differ by brand.  

However, following dose two, women who had received the Moderna brand were significantly more likely to report systemic side effects including chills, muscle/body aches, fever, vomiting.  

They were also more likely to report localised symptoms including pain, redness, swelling or itching at the injection site than those women who had had dose two of the Pfizer vaccine.  

A small proportion of women following dose one of either vaccine reported a reduction in milk supply.  There was a significant difference in reduction of milk supply following dose two by brand, 8% for Pfizer, 23.4% for Moderna.  

However, in all cases milk production returned to normal within 72 hours.  

Three women reported a change in colour of milk to blue green following dose one and two reported a change in colour of milk following dose two. 

Few events were reported for children following maternal vaccination with either brand or either dose.  

The most common child event following dose two was irritability 10.3% and 10.4% for Pfizer and Moderna respectively.  

Poor sleep 7.8% and 8.3% for Pfizer and Madonna respectively, with significantly more drowsiness reported for children whose mother had received the Moderna versus the Pfizer vaccine, 0% versus 6.4%.  

The researchers concluded that greater than 85% of participants reported any symptom for both Pfizer and Moderna vaccine following either dose.  

This is substantially higher than the 61-67% of women who reported any symptom previously.  

This could be due to differences in methods of assessment, timing and number of symptoms specifically questioned.  

However, consistent with adult participation in clinical trials for each vaccine, they noted increased frequencies of most symptoms following the second dose compared to the first.  

They also found a significantly greater frequency of localised pain, redness, swelling and itching at the injection site. As well as systemic symptoms including chills, muscle body aches, fever and vomiting following dose two of the Moderna vaccine versus the Pfizer vaccine.  

Some participants reported a reduction in milk supply, which in all cases did, however, return to normal.  

They found a lower frequency of any event reported in children, all of which were non-serious.  

They argue that their data is reassuring regarding the safety of vaccination in breastfeeding women and their breastfed children with either of the mRNA COVID-19 vaccines.  

They further argue that additional studies are required to evaluate milk composition and antibody status in samples obtained from women participating in the current study.

An interesting study which suggests that vaccination in breastfeeding women is safe, but the efficaciousness is not as yet known.  

The London General Practice as the leading London doctors’ clinic commends the Government on its COVID vaccination programme and encourages all those applicable to consider and have vaccination.  

The London General Practice has developed a full programme of COVID testing, including PCR swabs, antibody testing, same day COVID testing and rapid antigen tests.

Dr Paul Ettlinger

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