Despite a recent endorsement from official and professional bodies unequivocally recommending COVID-19 vaccination, vaccine hesitancy among pregnant people remains high. The accumulated evidence demonstrates that pregnant people are a special risk group for COVID-19, with an increased risk of intensive care unit admission, extracorporeal membranous oxygenation requirement, preterm birth, and perinatal death. These risks are further increased with some variants of concern, and vaccination of pregnant people reduces the COVID-19–related increase in maternal or fetal morbidity. Data from more than 180,000 vaccinated persons show that immunization against COVID-19 with an mRNA vaccine is safe for pregnant people. Many observational studies comparing perinatal outcomes between vaccinated and unvaccinated pregnant people have had reassuring findings and did not demonstrate harmful effects on pregnancy or the newborn. Immunization with mRNA vaccines does not increase the risk of miscarriage, preterm delivery, low birthweight, maternal or neonatal intensive care unit admission, fetal death, fetal abnormality, or pulmonary embolism. Moreover, observational data corroborate the findings of randomized trials that mRNA vaccination is highly effective at preventing severe SARS-CoV-2 infection in pregnant people, emphasizing that the potential maternal and fetal benefits of vaccination greatly outweigh the potential risks of vaccination. Ensuring pregnant people have unrestricted access to COVID-19 vaccination should be a priority in every country worldwide.
Introduction
The rapid accumulation of data on COVID-19 and pregnancy during the pandemic resulted in many recommendations from professional bodies, which may, in retrospect, seem contradictory. This is especially true for COVID-19 vaccination during pregnancy. Pregnant people were not prioritized over their age-matched nonpregnant peers in the United States during the initial stages of vaccination rollout, and the Centers for Disease Control and Prevention (CDC) recommended that “getting vaccinated is a personal choice” owing to the lack of substantial safety data. In addition, a cautious approach was employed in other countries, such as the United Kingdom. Initially, pregnant people were recommended vaccination only if they were considered to be at increased risk of acquiring COVID-19 (such as healthcare workers) or having severe diseases if infected (such as those with underlying medical conditions). The World Health Organization (WHO) recommended vaccinating pregnant people “where the benefits outweigh the risks” until they changed their position to endorsement in November 2021. The accumulation of safety data and increasing evidence of substantial harms of COVID-19 to pregnant people led many professional organizations to fortify their stance, and they now unequivocally “recommend” vaccination of pregnant people. The Royal College of Obstetricians and Gynaecologists (RCOG), the American College of Obstetricians and Gynecologists (ACOG), the Society for Maternal-Fetal Medicine, and the CDC recommend that all pregnant people should be vaccinated. , Many countries underwent substantial policy changes during the pandemic as more permissive policies for vaccination of pregnant people were adopted worldwide. The COVID-19 maternal immunization tracker, a joint initiative by Johns Hopkins University and Berman Institute of Bioethics Center for Immunization Research, investigated and cataloged policy positions worldwide. As of April 2022, 162 countries recommend or permit COVID-19 immunization for some or all pregnant people compared with only 21 countries a year ago ( Figure ). Most recently, the CDC recommended urgent action to increase vaccination uptake among pregnant people, for whom the benefits of vaccination outweigh any potential or unknown risks.
Despite a strong endorsement from professional bodies, vaccine hesitancy among pregnant people remains high, and strategies that prioritize vaccination of pregnant people are needed. Vaccine hesitancy is particularly high among women who do not feel vulnerable to COVID-19 complications and lack access to accurate information about vaccine safety. Caregivers need to stay up to date with available evidence and provide thorough counseling to pregnant people at every stage of pregnancy.
COVID-19 in pregnancy: risk factors and perinatal complications
The susceptibility of pregnant people to severe disease, the mechanism of adverse effects on pregnancy outcomes, and the possibility of vertical transmission are yet to be fully ascertained. However, the accumulated body of evidence confirms that pregnant people are a special risk group for COVID-19. This is due not only to the direct effects of COVID-19 on pregnancy but also to the indirect effects of the pandemic, such as barriers to healthcare access affecting pregnancy outcomes. The risk factors for severe disease seem to be similar to those in nonpregnant people: socioeconomic deprivation; increased body mass index; Black and minority ethnicity; preexisting comorbidities, such as pregestational diabetes mellitus, hypertension, or chronic lung disease; and increased maternal age. Of note, 1 pregnancy-specific risk factor is timing of infection; women in their third trimester of pregnancy are more susceptible to severe disease, whereas critical COVID-19 rates are very low in the first trimester of pregnancy. This increased risk may be partly mediated through the physical burden on the lungs toward the end of pregnancy, as Pineles et al have shown that delivery stabilizes the deteriorating pO 2 -to-FiO 2 ratios in pregnant women with respiratory distress.
SARS-CoV-2 variants of concern are another risk factor with consideration implications on prognosis. Recent studies show that Delta wave infections were associated with increased morbidity and mortality among pregnant people and the risk of advanced respiratory support was increased. The finding was consistent among multiple centers worldwide. Omicron wave infections seem to be milder, but the data are often confounded by a high vaccination rate in the reported cohorts. Of note, 2 studies reported on the severity of Omicron infection among pregnant people and concluded that Omicron wave infection may be milder than Delta wave infection and not necessarily milder compared with pre-Delta variants. , The Omicron variant shows marked evasion of immunity elicited by the current generation of vaccines. A recent study showed that breakthrough infections during the Omicron wave were mild without a need for respiratory support for vaccinated individuals and that 5% of unvaccinated individuals needed oxygen supplementation. It is important to address the misconceptions about the decreased severity of SARS-CoV-2 with emerging variants and emphasize the need for vaccination despite the apparent decline of protection elicited by the vaccines.
COVID-19 vaccination in pregnant people
Since the start of the vaccination rollout in the United States, and now in the United Kingdom, the recommendation is that COVID-19 vaccination should be offered to all pregnant people in parallel with the rest of the population, according to their age group and comorbidities (Figure). After the initial ambiguous and rapidly changing guidance on COVID-19 vaccination in pregnant people, there is now a renewed effort to prioritize pregnant people as vaccination uptake remains particularly low in pregnancy. All pregnant people need to receive detailed counseling about the benefits of COVID-19 vaccination during pregnancy, including the provision of an up-to-date summary of safety data. Barriers to accessing a consultation with healthcare providers (ie obstetricians, midwives, or general practitioners) should be addressed, and question-and-answer format decision aids should be readily available.
Available vaccine types and recommendations by the Centers for Disease Control and Prevention
Of note, 3 types of COVID-19 vaccine (mRNA, viral vector, and inactivated) are currently available worldwide, and a fourth type (protein subunit) is awaiting approval by the Food and Drug Administration (FDA) ( Table 1 ). Vaccines using mRNA particles (Pfizer or Moderna) are by far the most commonly used type in pregnant people and have the largest accumulated safety data so far. In light of the accumulated safety data and established effectiveness against COVID-19, mRNA vaccines are recommended as the first choice for pregnant people. The development of mRNA vaccines was unprecedented, not only because of their novel mechanism of action but also because of the speed with which they were made available. Traditionally, it takes more than a decade to develop a vaccine and obtain regulatory approval. However, thanks to generous funding by governmental agencies (ie, Operation Warp Speed) and the colossal threat posed by the pandemic, this arduous and lengthy process was cut down to less than a year. These vaccines contain mRNA particles that prompt the muscle cells in the injection area to synthesize and express a portion of the SARS-CoV-2 spike protein. mRNA half-life is very short, so it remains in the tissue for only a few days. Antigen-presenting cells show mRNA uptake, which can be observed in regional lymph nodes in the days after the administration of the vaccine. For individuals who express vaccine skepticism because of the novel nature of mRNA vaccines, the following points should be made clear. First, mRNA particles cannot interact with hereditary genetic material and cannot change DNA. Second, dissemination in the body is limited mainly to the injection site and the regional lymph nodes, and transplacental passage is unlikely. Once committed, the primary vaccination schedule is considered complete after receiving 2 doses taken 3 to 8 weeks apart. There is no need to repeat the first dose if the second dose is delayed more than 2 months. Booster shots are recommended after at least 5 months after the primary vaccination series. Pregnant people without a competent immune system (organ transplant recipients, stem cell transplant, primary or acquired immunodeficiencies, etc.) are required to take 3 vaccines for their primary vaccination series, whereas booster shots are recommended 3 months after the primary vaccination series. Booster shots are required to reverse the decline in the humoral response, which is more pronounced in elderly people, but there are no pregnancy-specific data on the subject. COVID-19 vaccines can be taken with other vaccines in the same visit (flu; tetanus, diphtheria, and pertussis; etc.) without a waiting period. Finally, individuals with SARS-CoV-2 are still recommended to receive their scheduled COVID-19 vaccine after their quarantine period. This recommendation is the same for individuals with SARS-CoV-2 who received a monoclonal antibody treatment; they can be vaccinated as soon as their quarantine period ends.
| Vaccine type | Brands | US FDA approved | Recommended for pregnant people in the United States | Booster needed? a | Data on pregnancy outcomes |
|---|---|---|---|---|---|
| mRNA | Pfizer-BioNTech Moderna | Yes (Pfizer-BioNTech, Moderna) | Yes | At least 5 mo after completing primary COVID-19 vaccination series | Available |
| Viral vector | J&J Janssen AstraZeneca Gamaleya Research Institute | Yes (J&J Janssen) | Yes with reservations b | At least 2 mo after receiving J&J Janssen COVID-19 vaccination. mRNA booster is preferred | Limited availability |
| Inactivated | SinoPharm, Sinovac, Bharat Biotech | No | No | No recommendation | Limited availability |
| Protein subunit | Novavax | Under consideration | No | No recommendation | N/A |
a Centre for Disease Control and Prevention recommendation
b Individuals who had a severe reaction after an mRNA vaccine dose or who have a severe allergy to an ingredient of Pfizer-BioNTech or Moderna. Possibility of vaccine-induced thrombosis and thrombocytopenia should be disclosed.
In areas where mRNA vaccines are not widely available, viral vector and inactivated vaccines are also in common use, but safety data for these vaccines in pregnant people are unfortunately relatively lacking. Viral vector vaccines are not recommended for pregnant people in some countries (the United Kingdom and Canada), although the CDC states that they can be used in certain situations ( Table 1 ). Booster shots are recommended at least 2 months after a primary vaccination schedule with viral vector vaccines; the booster dose should be an mRNA vaccine.
Vaccine safety
The exclusion of pregnant people from the initial COVID-19 vaccine trials prevented the acquisition of pregnancy-specific safety data and limited the ability of professional organizations to make evidence-based recommendations on COVID-19 vaccination in pregnancy at the initial stage of vaccine implementation. To date, there are ongoing or planned randomized controlled trials of COVID-19 vaccines in pregnancy (Pfizer-BioNTech, Janssen vaccine [BNT16B2b2] Horizon 1 study, and the Preg-CoV pragmatic trial), which will explore the immunogenicity and reactogenicity of different vaccines and different schedules. However, the results from these trials are not expected before 2022 to 2023, and it is unclear whether trials will meet their target quota at all, given that vaccines are readily available and recommended to willing pregnant people outside the trial setting.
In the United States, pregnant or lactating women can choose any one of the vaccines licensed by the FDA. These include 2 mRNA vaccines (Pfizer-BioNTech [New York] and Moderna [mRNA1273; Cambridge, Massachusetts]) and 1 viral vector vaccine (Johnson & Johnson [J&J] Janssen [Titusville, New Jersey]). A large cohort of pregnant people is being followed up as part of the CDC V-safe and V-safe COVID-19 Vaccine Pregnancy Registry ( https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/vsafepregnancyregistry.html ). A preliminary report of more than 35,000 women, most vaccinated with an mRNA vaccine, identified no safety concern, and no “red flag signal” has been raised from the entire cohort. Several other vaccine safety surveillance systems are in place, including the Vaccine Adverse Event Reporting System (VAERS) implemented by the CDC in the United States, the Public Health England Inadvertent Vaccination in Pregnancy system, and the UK Medicines and Healthcare Products Regulatory Agency “Yellow Card” monitoring system. Public Health England and Public Health Scotland have reported that more than 81,000 pregnancies in England and more than 19,000 pregnancies in Scotland have received a COVID-19 vaccine. Reassuringly, reactogenicity rates seem to be similar in pregnant and nonpregnant individuals receiving the vaccine. Although pregnant people reported slightly higher rates of injection site pain, they reported lower rates of headache, myalgia, chills, and fever. A recent US study suggested that the incidence of adverse reactions, including fever, was lower in pregnant people compared with those who were neither pregnant nor lactating.
VAERS is an invaluable source for monitoring vaccine safety, but healthcare providers should be aware that the data have been misappropriated by some groups on social media, claiming vaccines are not safe for pregnant people. It is important to understand that social media is an important information source for some patients and knowledge level along with its sources may need to be queried. Clarifying that both the CDC and ACOG unequivocally recommend COVID-19 vaccination without reservations about its safety can be important for reducing vaccine hesitancy in some individuals.
Vaccine-associated myocarditis
Myocarditis following COVID-19 vaccination seems to be specific to mRNA vaccines. According to the US VAERS reports, there is an apparent increase in observed compared with expected rates of myocarditis following mRNA vaccination among young individuals. This increased risk is observed predominantly in males below 40 years of age. Published studies corroborate the VAERS reports, with cases occurring at a median age below 30 years, approximately 90% after the second dose, and overwhelmingly (98%) in males. In women of reproductive age, the potential risk of mRNA vaccine-associated myocarditis is approximately 2 and approximately 4 to 5 cases per million vaccinations (after the second dose) for women aged 25 to 40 years and 18 to 25 years, respectively. The excess risk of myocarditis that could be attributed to mRNA vaccination is <4 per million vaccination doses. Most cases of vaccine-associated myocarditis are mild and resolve spontaneously or with nonsteroidal antiinflammatory drugs. Vaccine-associated myocarditis should be suspected in pregnant people with chest pain, pressure, discomfort, shortness of breath, or palpitations occurring within approximately 5 days after vaccination. Elevated cardiac enzymes, abnormal cardiac rhythm, echocardiogram, or magnetic resonance imaging in the absence of other obvious causes should prompt consideration of vaccine-related myocarditis. Documentation of possible cases and outcomes is important for continued safety surveillance of mRNA vaccines. Reassuringly, in the hitherto published literature, there is no report of vaccine-associated myocarditis in the pregnant people.
Vaccine-induced thrombosis and thrombocytopenia
The rare syndrome of vaccine-induced thrombosis and thrombocytopenia (VITT), also known as thrombosis with thrombocytopenia syndrome (TTS), has been reported in rare instances with the viral vector vaccines (AstraZeneca and J&J Janssen) at a rate of 7 cases per million doses. The condition more commonly affects adults under the age of 50 years. It is an idiosyncratic reaction often occurring after the first dose of a vaccine but also possible after the second dose, although rarely. The condition does not seem to be more likely in those at prothrombotic risk, including pregnant people. Patients with VITT typically present within a few weeks of vaccination (approximately 5 to 30 days). , The diagnosis is more likely in persons presenting with thrombosis in atypical locations, such as splanchnic and cerebral veins, thrombocytopenia (<150×10 9 /L), and high D-dimer levels (>2000 μg/L). The exact pathogenesis of VITT is not clear, but antibodies against platelet factor 4 polyanion complexes were detected in most cases. In cases with clinical suspicion, the diagnosis can be confirmed by demonstrating platelet factor 4 antibodies using an enzyme-linked immunosorbent assay. The management of VITT is complex as patients are prone to both coagulopathy and hemorrhage. Intravenous immunoglobulin (IVIg) infusion is recommended to alleviate thrombocytopenia. Cases refractory to IVIg infusion have been successfully treated with plasma exchange. , Anticoagulation should be achieved with direct oral anticoagulants (fondaparinux, danaparoid, or argatroban), although concurrent bleeding is not a contraindication to anticoagulation, and decisions should be made on a case-by-case basis. The use of unfractionated heparin is not recommended as it may aggravate the condition. There is a single reported case of VITT in a pregnant people, who presented with headache, bilateral leg pain, and malaise 7 days after the first dose of AstraZeneca viral vector vaccine. She had mild thrombocytopenia (121×10 9 /L), but unfortunately, a diagnosis of VITT was not made at the time. The woman was readmitted with severe headache and thrombocytopenia (33×10 9 /L) 4 days after her initial discharge. Computed tomography revealed cerebral venous sinus thrombosis and parenchymal hemorrhage in the temporal lobe. Despite medical and surgical management of complications, both the mother and fetus died. This tragic case emphasized the importance of awareness of the condition.
Vaccination against SARS-CoV-2 using viral vector vaccines seems to be safe for pregnant people notwithstanding the extremely rare risk of VITT. Viral vector vaccines do not require stringent transfer and storage conditions and are more widely available in low- and middle-income countries (LMICs), where they may be of importance for preventing COVID-19–associated mortality and morbidity in pregnant people. As of December 14, 2021, the WHO Strategic Advisory Group of Experts has classified the Bharat Biotech Covaxin (BBV152 A, BBV152 B, BBV152 C; Hyderabad, India), Sinopharm BIBP-CorV (Hayat-Vax; Beijing, China), and Sinovac (CoronaVac; Beijing, China) (SARS-CoV-2–inactivated vaccine) vaccines to be “permitted” for pregnant people, which implies that all pregnant people can receive or choose to receive these vaccines.
In the United States, the advice is that pregnant people can be offered the viral vector vaccine with some reservations. They should be informed of the possible risk of VITT, particularly in individuals under the age of 50 years, and the fact that alternatives (ie, mRNA vaccines) are available.
Adverse perinatal outcomes following vaccination
Although regulatory bodies and public health agencies collect postmarketing surveillance data and monitor for safety signals, observational studies investigating perinatal outcomes in vaccinated women are equally important. Several studies compared perinatal outcomes between vaccinated and unvaccinated mothers, and the findings were reassuring. Table 2 lists the observational studies published before December 2021, reporting the perinatal outcomes of pregnant people who received COVID-19 vaccination during pregnancy and those who did not.
| Study | Sample size (of whom outcomes are reported) | Outcomes reported | Rate in vaccinated women, % (n/N) | Rate in unvaccinated women, % (n/N) | Effect estimate |
|---|---|---|---|---|---|
| Goldshtein et al, 2021 | 7530 vaccinated vs 7530 unvaccinated | SARS-CoV-2 infection (≥28 d after the first dose) | 0.2 (10/4788) | 1.0 (46/4788) | OR: 0.21 (95% CI, 0.09–0.43) |
| Abortion | 1.7 (128/7530) | 1.6 (118/7530) | OR: 1.08 (95% CI, 0.83–1.41) | ||
| Fetal growth restriction | 0.5 (36/7530) | 0.5 (38/7530) | OR: 0.94 (95% CI, 0.58–1.53) | ||
| Preeclampsia | 0.3 (20/7530) | 0.3 (21/7530) | OR: 0.95 (95% CI, 0.48–1.84) | ||
| Stillbirth | <0.1 (1/7530) | <0.1 (2/7530) | OR: 0.49 (95% CI, 0.01–9.60) | ||
| Maternal death | 0.0 (0/7530) | 0.0 (0/7530) | Not estimable | ||
| Pulmonary embolism | 0.0 (0/7530) | 0.0 (0/7530) | Not estimable | ||
| Preterm birth at <37 wk | 5.6 (77/1387) | 5.9 (85/1427) | OR: 0.92 (95% CI, 0.66–1.29) | ||
| Blakeway et al, 2022 | 133 vaccinated vs 399 unvaccinated | SGA | 12.0 (16/133) | 12.0 (48/399) | OR: 1.00 (95% CI, 0.55–1.82) |
| Fetal abnormalities | 2.3 (3/133) | 2.5 (10/399) | OR: 0.89 (95% CI, 0.24–3.31) | ||
| Stillbirth | 0.0 (0/133) | 0.2 (1/399) | Not estimable | ||
| Cesarean delivery | 30.8 (41/133) | 34.1 (136/399) | OR: 0.86 (95% CI, 0.56–1.31) | ||
| Postpartum hemorrhage | 9.8 (13/133) | 9.0 (36/399) | OR: 1.09 (95% CI, 0.56–2.12) | ||
| Intrapartum fever | 3.7 (5/133) | 1.0 (4/399) | OR: 3.85 (95% CI, 1.01–14.60) | ||
| Placental abruption | 0.0 (0/133) | 0.0 (0/133) | Not estimable | ||
| NICU admission | 5.3 (7/133) | 5.0 (20/399) | OR: 1.05 (95% CI, 0.43–2.54) | ||
| Maternal ICU admission | 6.0 (8/133) | 4.0 (16/399) | OR: 1.53 (95% CI, 0.64–3.66) | ||
| Theiler et al, 2021 | 140 vaccinated vs 1862 unvaccinated | SARS-CoV-2 infection (any time) | 1.4 (2/140) | 11.3 (210/1862) | OR: 0.11 (95% CI, 0.01–0.42) |
| Maternal death | 0.0 (0/140) | 0.0 (0/1862) | Not estimable | ||
| Pulmonary embolism | 0.0 (0/129) | 0.1 (2/1580) | Not estimable | ||
| Early neonatal death | 0.0 (0/140) | 0.0 (0/1862) | Not estimable | ||
| NICU admission | 0.7 (1/140) | 0.5 (11/1862) | OR: 1.31 (95% CI, 0.03–9.17) | ||
| Maternal ICU admission | 0.7 (1/140) | 0.1 (2/1862) | OR: 7.24 (95% CI, 0.12–14.02) | ||
| Postpartum hemorrhage | 4.3 (6/140) | 3.1 (57/1862) | OR: 1.54 (95% CI, 0.53–3.67) | ||
| Transfusion | 17.8 (25/140) | 12.9 (241/1862) | OR: 1.61 (95% CI, 0.97–2.58) | ||
| Cesarean delivery | 31.4 (44/140) | 29.8 (555/1862) | OR: 1.21 (95% CI, 0.81–0.80) | ||
| Preeclampsia or eclampsia | 0.7 (1/140) | 1.2 (23/1862) | OR: 0.62 (95% CI, 0.01–3.91) | ||
| Stillbirth | 0.0 (0/140) | 0.4 (6/1862) | Not estimable | ||
| Low birthweight (<2500 g) | 2.1 (3/140) | 6.5 (121/1862) | OR: 0.34 (95% CI, 0.07–1.05) | ||
| Beharier et al, 2021 | 92 vaccinated vs 66 unvaccinated | Preterm birth at <37 wk | 4.3 (4/92) | 7.6 (5/66) | OR: 0.55 (95% CI, 0.10–2.70) |
| NICU admission | 4.3 (4/92) | 1.5 (1/66) | OR: 2.93 (95% CI, 0.28–14.76) | ||
| Dagan et al, 2021 | 10,861 vaccinated vs 10,861 unvaccinated | SARS-CoV-2 infection (≥28 d after the first dose) | 0.04 (3/7577) | 0.80 (64/7519) | RR: 0.04 (95% CI, 0.00–0.11) |
| Kharbanda et al, 2021 | 15,079 vaccinated vs 90,367 unvaccinated | Miscarriage | Vaccination rate in miscarriages is 8.6 (1128/13,160) Vaccination rate in ongoing pregnancies is 8.0(20,139/250,944) | OR: 1.02 (95% CI, 0.96–1.08) | |
| Rottenstreich et al, 2022 | 712 vaccinated vs 1063 unvaccinated | Preterm birth at <37 wk | 1.0 (7/712) | 0.9 (10/1063) | OR: 1.04 (95% CI, 0.33–3.05) |
| Cesarean delivery | 15.6 (111/712) | 10.8 (115/1063) | OR: 1.04 (95% CI, 0.33–3.05) | ||
| Postpartum hemorrhage | 7.3 (52/712) | 10.0 (106/1063) | OR: 0.71 (95% CI, 0.49–1.01) | ||
| Placental abruption | 1.1 (8/712) | 2.3 (25/1063) | OR: 0.47 (95% CI, 0.18–1.08) | ||
| Maternal ICU admission | 0.0 (0/712) | 0.0 (0/1063) | Not estimable | ||
| Transfusion | 0.5 (4/712) | 0.6 (7/1063) | OR: 0.85 (95% CI, 0.18–3.36) | ||
| Puerperal fever | 3.2 (23/712) | 3.4 (36/1063) | OR: 0.95 (95% CI, 0.53–1.66) | ||
| Magnus et al, 2021 | 1003 vaccinated vs 17,474 unvaccinated | Miscarriage within the 5-wk exposure window | 23.0 (231/1003) | 24.5 (4290/17474) | OR: 0.91 (95% CI, 0.75–1.10) |
| Wainstock et al | 913 vaccinated vs 3486 unvaccinated | Hypertensive disorders of pregnancy | 5.5 (50/913) | 4.7 (165/3486) | OR: 1.17 (95% CI, 0.84–1.61) |
| 5-min Apgar score of <7 | 0.4 (2/913) | 1.1 (30/3486) | OR: 0.33 (95% CI, 0.08–1.40) | ||
| Cesarean delivery | 19.9 (182/913) | 17.2 (601/3486) | OR: 1.19 (95% CI, 0.99–1.44) | ||
| Placental abruption | 0.3 (3/913) | 0.3 (11/3486) | OR: 1.04 (95% CI, 0.29–3.74) | ||
| Postpartum hemorrhage | 1.1 (10/913) | 0.9 (30/3486) | OR: 1.28 (95% CI, 0.62–2.62) | ||
| Postpartum fever | 0.2 (2/913) | 0.3 (12/3486) | OR: 0.64 (95% CI, 0.14–2.85) | ||
| SGA | 2.8 (26/913) | 3.8 (131/3486) | OR: 0.75 (95% CI, 0.49–1.15) | ||
| Butt et al | 407 vaccinated vs 407 unvaccinated | SARS-CoV-2 infection | 10.5 per 10,000 person-weeks | 82.5 per 10,000 person-weeks | HR: 0.12 (95% CI, 0.03–0.56) |
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