Study: Most COVID-19 vaccine side effects mild in pregnant, breastfeeding people

COVID-19 vaccine side effects are common in pregnant people and those who are breastfeeding, but researchers said they generally are mild. File Photo by Debbie Hill/UPI
1 of 5 | COVID-19 vaccine side effects are common in pregnant people and those who are breastfeeding, but researchers said they generally are mild. File Photo by Debbie Hill/UPI | License Photo

Aug. 17 (UPI) -- Side effects to the three COVID-19 vaccines available in the United States are relatively common, most are mild -- such as pain at the injection site -- and none had a serious effect on a pregnancy, a study published Tuesday by JAMA Network Open found.

About 90% of pregnant people in the study reported injection-site pain after the first and second dose of the vaccine, about the same percentage as non-pregnant people in the study, while 30% indicated they experienced fatigue after the first dose and 61% did so following the second, the data showed.


Pregnant participants, overall, were half as likely to suffer serious symptoms of these side effects after either dose of the vaccine than those who were not pregnant, the researchers said.

Fewer than one in 10 people breastfeeding newborns following childbirth reported a decline in milk supply after receiving the second dose of a two-shot COVID-19 vaccine.


Five percent reported a disruption in milk supply after the first dose of the vaccine, and just over 7% cited the issue after the second dose.

"Our study shows that COVID-19 vaccines were well tolerated by pregnant and lactating women, as well as women planning pregnancy and provides further data that pregnant, breastfeeding individuals," study co-author Dr. Alisa Kachikis told UPI in an email.

"Those planning pregnancy in the near future should feel quite reassured about getting a COVID-19 vaccine," said Kachikis, a maternal-fetal medicine specialist at UW Medicine in Seattle.

Since the start of the pandemic, studies on the effects of COVID-19 have yielded conflicting results, though the majority, including one published last week by JAMA Network Open, suggest that the virus raises the risk for preterm delivery and other complications.

Pregnant people are also more likely to develop serious illness following infection, according to the Centers for Disease Control and Prevention.

A report issued by agency researchers found that there are "no safety concerns" for any of the COVID-19 vaccines -- the two-dose Moderna and Pfizer-BioNTech and the one-dose Johnson & Johnson -- in pregnant people or those who are breastfeeding.

Because of this data, the agency revised its guidance Aug. 11 to recommend that all pregnant people and those breastfeeding get vaccinated against the virus.


For this study, Kachikis and her colleagues compiled side effect reports among roughly 7,800 people who were pregnant, 6,800 who were breastfeeding and 2,900 who were neither pregnant nor breastfeeding, but planned to become pregnant.

Fewer than 100 of the study participants did not receive at least one dose of a COVID-19 vaccine, the researchers said.

Just over 60% of them completed the two-dose course of the Pfizer-BioNTech vaccine, while 38% had the Moderna vaccine and less than 1% opted for the Johnson & Johnson vaccine, according to the researchers.

Nearly half of the pregnant people in the study received their vaccines during the second trimester, while about 28% did so during the third.

Among all participants, 97% reported post-vaccination reactions after the first dose, with the most common reactions being pain at injection site, in 91%, and fatigue, in 31%.

Nearly 70% of study participants who received the Pfizer-BioNTech vaccine experienced fatigue after the second dose, compared with more than 80% of those given the Moderna shots.

With both vaccines, pregnant people were about twice as likely to report fatigue after vaccination compared to non-pregnant people and those who were lactating, according to the researchers

In addition, about 40% of pregnant people reported muscle pain or headache after getting their second dose of the Pfizer-BioNTech vaccine, while more than 60% of those given the Moderna shot did so.


People in the study who were not pregnant at the time of vaccination, or those who were breastfeeding, were about half as likely to report these side effects.

Although the study assessed vaccine-related side effects in nearly 8,000 pregnant people, the researchers did not address the outcomes of their pregnancies.

Roughly 95% of pregnant participants were still expecting at the conclusion of the study and just over 4% had given birth, while less than 1% suffered a miscarriage.

"Pregnant people should get vaccinated," Kachikis said.

"Not only will it protect the pregnant person from getting severe COVID-19 illness but ... antibodies transferred to the baby over the placenta during pregnancy and in breastmilk after delivery may also help provide some protection to the newborn baby," she said.

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