Most newborns who encounter SARS-CoV-2 do well. In a large U.S. study, COVID-19 was diagnosed in roughly one in a thousand neonatal hospital encounters, and only about 8 percent of those cases were classified as severe.1Pediatrics. Epidemiology of Neonatal COVID-19 in the United States That reassuring baseline, though, coexists with real dangers in specific circumstances: placental damage during pregnancy, a rare inflammatory syndrome triggered by maternal infection, and the particular vulnerability of preterm or medically fragile infants. Understanding when the risk is low and when it spikes makes a meaningful difference in the decisions parents and clinicians face.
How the Virus Reaches a Newborn
There are two broad routes. The first is vertical transmission, meaning the virus passes from mother to baby before or during birth, either through the placenta, during delivery, or through very early contact. The second is horizontal transmission, the familiar person-to-person spread through respiratory droplets and contaminated surfaces after the baby is born.
Vertical transmission gets most of the research attention because it is harder to prevent. A 2025 meta-analysis pooling over 200 studies estimated the rate at about 4 percent among babies born to mothers who tested positive.2Journal of Infection and Public Health. COVID-19 vertical transmission from mothers to neonates: A systematic review and meta-analysis of 204 studies That number varied widely across studies, partly because of differences in when and how babies were tested. Some smaller studies found no evidence of transmission at all, with negative results from amniotic fluid, colostrum, and newborn throat swabs.3medRxiv. Evaluation of vertical transmission of SARS-CoV-2 in utero: nine pregnant women and their newborns The consensus is that vertical transmission happens but is uncommon compared to the everyday postnatal exposure a baby gets from infected caregivers.
Horizontal transmission after birth is far more typical. Newborns can pick up the virus from a parent, sibling, or hospital visitor, especially in households where infection-control precautions are limited. One case report described an asymptomatic neonate who likely acquired the virus from family members, underscoring that even without obvious symptoms in the household, the virus can find its way to the baby.4Nigerian Journal of Paediatrics. Probable horizontal transmission of SARS-CoV-2 in an asymptomatic neonate: A case report
What Happens in the Placenta
The placenta is the gatekeeper between a pregnant person’s bloodstream and the fetus. SARS-CoV-2 enters human cells by latching onto a receptor called ACE2, and the placenta does express this receptor, particularly in the outer cell layer that lines the placental villi and sits right at the interface between maternal and fetal blood.5PubMed Central. Consistent localization of SARS-CoV-2 spike glycoprotein and ACE2 over TMPRSS2 predominance in placental villi of 15 COVID-19 positive maternal-fetal dyads A second protein the virus typically needs for entry, TMPRSS2, is present in much lower amounts in placental tissue, which may partially explain why the virus does not cross the placenta as efficiently as it infects the lungs.6Nature Cell Biology. A placental model of SARS-CoV-2 infection reveals ACE2-dependent susceptibility and differentiation impairment in syncytiotrophoblasts
When the virus does infect the placenta, the consequences can be devastating even without infecting the fetus directly. A pattern known as SARS-CoV-2 placentitis involves massive fibrin deposits, chronic inflammation, and destruction of the cells that keep the placenta functioning. In the most severe cases, this damage can affect more than three-quarters of the placental tissue, effectively cutting off the oxygen supply to the fetus.7PubMed Central. Stillbirth after COVID-19 in Unvaccinated Mothers Can Result from SARS-CoV-2 Placentitis, Placental Insufficiency, and Hypoxic Ischemic Fetal Demise, Not Direct Fetal Infection This mechanism was linked to stillbirths and neonatal deaths during the pandemic, particularly among unvaccinated mothers.8PubMed Central. SARS-CoV-2 placentitis, stillbirth, and maternal COVID-19 vaccination: clinical-pathologic correlations The baby itself may never test positive for the virus; it is the organ damage to the placenta that causes the harm.
How Sick Do Infected Newborns Get
The short answer for most newborns: not very. In U.S. data, nearly two-thirds of neonates diagnosed with COVID-19 had no signs of infection at all when they first came to medical attention. The most common symptoms in those who did get sick were rapid breathing and fever. About 8 percent of diagnosed neonates met criteria for severe infection, and those babies were far more likely to need breathing support.1Pediatrics. Epidemiology of Neonatal COVID-19 in the United States
When onset matters: a study comparing early-onset cases (symptoms in the first few days of life, suggesting vertical or perinatal infection) with late-onset cases (symptoms developing later, likely from postnatal exposure) found that early-onset infections were more often asymptomatic. Late-onset infections accounted for the vast majority of mild and moderate cases. Across both groups, all patients were eventually cured and discharged, and no critical cases were observed.9PubMed Central. Comparison of neonatal COVID-19 clinical features based on onset timing
The picture changes when the mother had moderate to severe COVID during pregnancy. In one study of 200 pregnant women with COVID-19, those with moderate-to-severe disease were roughly six times as likely to deliver preterm and their babies were more than nine times as likely to have low birth weight compared to babies of mothers with mild or asymptomatic infection. Neonatal ICU admissions were ten times higher in the moderate-to-severe group.10Scientific Reports. Investigating the association between severity of COVID-19 infection during pregnancy and neonatal outcomes A broader synthesis confirmed the pattern: pregnant women diagnosed with COVID-19 had higher rates of preterm birth, cesarean delivery, and low birth weight compared to uninfected women.11PubMed Central. The impact of COVID-19 infections on pregnancy outcomes in women
The Neonatal Inflammatory Syndrome
One of the scarier complications, thankfully rare, is multisystem inflammatory syndrome in neonates, or MIS-N. This is not a direct viral infection of the baby’s organs but rather an overreaction of the immune system, triggered by exposure to maternal COVID-19 antibodies or viral particles. The heart and lungs are most commonly affected. A systematic review of 58 cases found cardiac involvement in about two-thirds and respiratory problems in a similar proportion. Fever was present in roughly half the cases.12Seminars in Fetal and Neonatal Medicine. Multisystem inflammatory disease in neonates (MIS-N) due to maternal COVID-19
Treatment typically involves corticosteroids and intravenous immunoglobulin, both of which were used in the vast majority of documented cases. Blood thinners were sometimes added when clotting markers were elevated. The rarity of MIS-N makes it difficult to study systematically, but awareness of the condition matters because symptoms can appear in the first days of life, before the baby has even had postnatal viral exposure. A newborn presenting with unexplained cardiac dysfunction and elevated inflammatory markers, born to a mother who had COVID-19 during pregnancy, should raise suspicion.
How Infants Fight the Virus Differently
Newborns have an immune system that is still calibrating itself, which has both upsides and downsides for a SARS-CoV-2 encounter. Research comparing infant and adult immune responses found that in severely ill infants, certain immune cells shifted almost entirely into a heightened antiviral state, a pattern that was only partially observed in severely ill adults.13Nature Communications. SARS-CoV-2 induced immune perturbations in infants vary with disease severity and differ from adults’ responses This suggests that infants mount a qualitatively different immune response: perhaps more all-or-nothing, with immune cells committing fully to the fight rather than splitting their efforts. Whether that full commitment is protective or contributes to inflammation in severe cases is an area of active investigation.
Protection Through Maternal Vaccination
The single most effective way to protect a newborn from COVID-19 begins before birth. When a pregnant person is vaccinated, antibodies cross the placenta and give the baby a head start. Studies consistently show that mRNA vaccination during pregnancy produces efficient antibody transfer, with median transfer ratios above 1.5, meaning the baby is born with higher antibody levels than the mother has at the time of delivery.14PubMed Central. COVID-19 booster vaccination during pregnancy enhances maternal binding and neutralizing antibody responses and transplacental antibody transfer to the newborn In one cohort, nearly 97 percent of vaccinated mothers and their cord blood samples tested positive for anti-spike antibodies.15PubMed Central. Immune Response and Transplacental Antibody Transfer in Pregnant Women after COVID-19 Vaccination
Timing of the vaccine during pregnancy matters. Getting vaccinated earlier in the third trimester, rather than close to the due date, gives the placenta more time to pump antibodies across. One study found that early third-trimester vaccination produced higher neonatal antibody concentrations and dramatically better transfer ratios for neutralizing antibodies compared to vaccination late in the third trimester.16PubMed Central. Timing of SARS-CoV-2 vaccination during the third trimester of pregnancy and transplacental antibody transfer: a prospective cohort study The second trimester or early third trimester appears to be the sweet spot.
How long do those borrowed antibodies last in the baby? The half-life of vaccine-induced antibodies in infants is roughly five weeks, with binding antibodies declining by half every 35 to 37 days.17Pediatrics. Infant Antibodies After Maternal COVID-19 Vaccination During Pregnancy or Postpartum Despite this steady decline, detectable antibodies persisted in most infants through six months.18iScience. Placental transfer dynamics and durability of maternal COVID-19 vaccine-induced antibodies in infants Vaccination also dramatically outperformed natural infection in this regard: at six months, 57 percent of infants born to vaccinated mothers still had detectable antibodies, compared to just 8 percent of those born to mothers who had been infected but unvaccinated.19JAMA. Durability of Anti-Spike Antibodies in Infants After Maternal COVID-19 Vaccination or Natural Infection
What Breastfeeding Adds
Breast milk delivers a different type of protection from what the placenta provides. While placental transfer is dominated by IgG antibodies circulating in the blood, breast milk is rich in secretory IgA, which coats the lining of the baby’s mouth, throat, and gut, acting as a local barrier right where the virus tries to enter.
After maternal infection, the IgA response in breast milk is both strong and long-lasting. One study found that nearly 90 percent of milk samples still had spike-specific IgA above the positive threshold nine to twelve months after infection, and half of participants showed less than a twofold decline over that entire period.20PubMed Central. The Secretory IgA Response in Human Milk Against the SARS-CoV-2 Spike Is Highly Durable and Neutralizing for At Least 1 Year of Lactation Postinfection Vaccination produces a similar milk antibody response, with detectable IgA, IgG, and neutralizing antibodies persisting for up to six months post-vaccination. Mothers who had both infection and vaccination showed the highest antibody levels at three months, consistent with the broader concept of hybrid immunity.21PubMed. Preservation of Anti-SARS-CoV-2 Neutralizing Antibodies in Breast Milk: Impact of Maternal COVID-19 Vaccination and Infection
Crucially, SARS-CoV-2 itself does not appear to transmit through breast milk in any meaningful way. The antibodies are present; live, transmissible virus is not. This is why major health organizations consistently encouraged breastfeeding even when the mother was actively infected, provided basic hygiene precautions like hand washing and mask wearing were followed.
Rooming-In Versus Separation
Early in the pandemic, many hospitals separated COVID-positive mothers from their newborns. The logic seemed straightforward: keep the virus away from the baby. But the practice came at a steep cost, disrupting breastfeeding, delaying bonding, and increasing maternal anxiety. As more data accumulated, the picture shifted. A retrospective study of protected rooming-in, where mothers and infants stayed together with infection-control precautions in place, found that none of the enrolled infants were hospitalized for COVID-19 and exclusive breastfeeding rates at discharge were actually higher than among separated pairs.22PubMed. Rooming-In Practice During the Pandemic: Results From a Retrospective Cohort Study
The psychosocial toll of separation also left marks. Mothers who experienced pandemic-era restrictions reported that limited partner presence in the maternity ward, inability to see relatives, and early interactions with their newborn while wearing a mask altered the bonding experience.23PubMed Central. Postnatal mental health during the COVID-19 pandemic: Impact on mothers’ postnatal sense of security and on mother-to-infant bonding These findings contributed to the shift in hospital policies toward keeping mothers and babies together unless the mother is too ill to provide care.
How Different Variants Changed the Picture
Not all waves of the pandemic posed the same risk to pregnant women and their babies. A prospective registry across France and Switzerland tracked outcomes during the pre-Delta, Delta, and Omicron periods among unvaccinated pregnant women. The Delta wave was the most dangerous: severe maternal outcomes were reported in about 6.5 percent of cases, roughly double the rate during the pre-Delta period. The Omicron period, by contrast, brought the lowest maternal risk at around 1 percent, about a third of the pre-Delta rate.24The Lancet Regional Health – Europe. Maternal and perinatal outcomes following pre-Delta, Delta, and Omicron SARS-CoV-2 variants infection among unvaccinated pregnant women in France and Switzerland These differences reflected the general pattern seen in the broader population: Delta hit harder, and Omicron, while more transmissible, caused less severe illness on average. But the data came from unvaccinated women, so the effect of the variant itself is somewhat separated from the protection offered by immunity.
Treatment When a Newborn Is Severely Ill
Treatment options for neonatal COVID-19 are limited and largely borrowed from pediatric and adult protocols with dose adjustments. Remdesivir, the antiviral that became a mainstay of adult COVID treatment, has been used in severe neonatal cases. A small case series reported no side effects during or after administration, with follow-up out to ten months showing no complications.25Archives of Pediatric Infectious Diseases. The Drug Effectiveness and Side Effects of Remdesivir in Neonatal COVID-19: A Case Series Study Larger pediatric studies found that remdesivir was generally well tolerated, with the most common side effects being drops in albumin levels and mild anemia rather than the liver or kidney toxicity that clinicians initially worried about.26PubMed Central. Efficacy and Safety of Remdesivir in Hospitalized Pediatric COVID-19: A Retrospective Case-Controlled Study
The evidence base for treating neonates specifically remains thin. Most of the data comes from case series and retrospective reviews rather than randomized trials, which are extraordinarily difficult to conduct in this population. For the rare newborn who develops severe respiratory disease from COVID-19, supportive care, including supplemental oxygen and mechanical ventilation if needed, remains the backbone of treatment, with antivirals reserved for the sickest patients.
Neurodevelopmental Concerns After Prenatal Exposure
One of the murkier areas of research involves what happens in the longer term to children who were exposed to SARS-CoV-2 in utero. A study tracking neurodevelopmental outcomes in early childhood found a modestly elevated risk of autism spectrum disorder diagnosis among girls whose mothers had been infected during pregnancy, with no similar increase seen in boys. The same study found a slightly lower risk of motor delay in boys exposed prenatally. Neither sex showed any association between prenatal exposure and speech or language delays.27Translational Psychiatry. SARS-CoV-2 infection during pregnancy and neurodevelopmental outcomes in early childhood
These findings are preliminary and should be interpreted cautiously. The effect sizes are small, the follow-up periods are short by neurodevelopmental standards, and separating the effects of the virus itself from the stress, isolation, and healthcare disruption of the pandemic is extremely difficult. Still, they illustrate why researchers continue to follow pandemic-era birth cohorts: the developing brain is sensitive to maternal immune activation, and it will take years before the full picture emerges.
Practical Steps for Protecting a Newborn
For parents expecting a baby or already caring for one, the evidence points toward a few concrete strategies:
- Vaccinate during pregnancy: mRNA COVID-19 vaccination in the second or early third trimester produces the best antibody transfer to the baby and provides protection that lasts months after birth.
- Breastfeed if possible: breast milk delivers secretory antibodies directly to the mucosal surfaces where the virus enters, and this protection persists for months regardless of whether it came from vaccination or prior infection.
- Keep the baby close: rooming-in with basic hygiene measures is preferable to separation, which disrupts feeding and bonding without clearly reducing infection risk.
- Limit close contacts early on: because horizontal transmission is the dominant route of neonatal infection, limiting the number of people who handle the baby in the first weeks, especially anyone with respiratory symptoms, makes a practical difference.
- Watch for warning signs: rapid breathing, fever, poor feeding, and unusual lethargy in a newborn warrant prompt medical attention, especially if there has been a known COVID-19 exposure.
The pandemic’s most dangerous phase for pregnant women and newborns has passed, thanks to population-level immunity and less virulent circulating variants. But SARS-CoV-2 has not disappeared, and the virus continues to evolve. The tools available now, particularly maternal vaccination and breastfeeding, offer layers of protection that did not exist during the earliest and deadliest waves. For a newborn’s immune system, still weeks or months away from being able to mount its own robust response, those borrowed defenses matter.