Large Study Confirms COVID Vaccination During Pregnancy Protects Infants

A three-year Norwegian study tracking 146,031 children has added the most substantial evidence yet that COVID-19 vaccination during pregnancy shields infants from hospitalization in their first months of life — a period when they are too young to be vaccinated themselves [1]. Published in the journal Pediatrics on March 25, 2026, the research lands in the middle of a widening gap between scientific consensus and U.S. federal health policy.

The Study: Scope and Findings

Researchers led by Dr. Helena Niemi Eide at the University of Oslo followed children born between March 2020 and December 2023, drawing on Norway's comprehensive national health registries to track medical outcomes for up to two years after birth [1]. Roughly one in four mothers in the cohort received a COVID-19 vaccine during pregnancy. The study received funding from the University of Oslo and Scandinavian government agencies, with no pharmaceutical company involvement [1].

The central finding: infants whose mothers were vaccinated were approximately 50% less likely to be hospitalized for COVID-19 in their first two months of life compared to infants of unvaccinated mothers [1]. Between three and five months of age, the risk reduction narrowed to 24% [1]. By six months, the protective effect had worn off — consistent with the known half-life of maternally transferred antibodies.

The study also addressed a persistent concern among vaccine skeptics: that prenatal vaccination might broadly weaken an infant's immune system. It found no increased risk of hospitalization for infections of any kind among vaccine-exposed infants [1]. Vaccinated mothers' babies were 5% more likely to visit primary care, a finding the researchers attributed to health-seeking behavior rather than increased illness [1].

How It Compares to Earlier Research

The Norwegian study is not the first to document this protective effect, but its size and duration make it the most robust population-level confirmation to date.

A landmark study published in the New England Journal of Medicine in 2022 found that maternal vaccination with two doses of mRNA vaccine was associated with a 52% reduction in COVID-19 hospitalization among infants under six months, and a 70% reduction in ICU admissions [2]. That study also revealed significant variation by variant: vaccine effectiveness reached 80% during the delta-predominant period but dropped to 38% during the omicron wave [2].

CDC surveillance data from 17 states between July 2021 and January 2022 corroborated these findings, showing that the incidence of infant COVID hospitalization was roughly five times higher among babies of unvaccinated mothers (100 per 100,000 person-years) than among babies of vaccinated mothers (21 per 100,000 person-years) [3].

A more recent MMWR report covering October 2022 through April 2024 documented a troubling trend: among 1,470 COVID-associated infant hospitalizations across 12 states, 87.5% of infants had no documentation of maternal vaccination during pregnancy [4]. Maternal vaccination rates among mothers of hospitalized infants plummeted from 17.6% in the 2022–23 season to just 4.3% in 2023–24 [4].

Source: New England Journal of Medicine

Data as of Mar 27, 2026CSV

The Biology: How Maternal Antibodies Protect Newborns

The mechanism behind this protection is transplacental antibody transfer — a process that occurs primarily in the third trimester. The placenta actively captures immunoglobulin G (IgG) antibodies from the mother's bloodstream and ferries them to the fetus via specialized receptors called neonatal Fc receptors (FcRn) [5].

Not all IgG subtypes cross equally. Research published in Nature Communications documented a transfer hierarchy: IgG1 crosses most efficiently, followed by IgG3, IgG4, and IgG2 [5]. The placenta also preferentially transfers antibodies that activate natural killer (NK) cells — a class of white blood cells that form a critical part of neonatal innate immune defense [5].

Timing matters. The NEJM study found that vaccine effectiveness was significantly higher when the second dose was administered after 20 weeks of pregnancy (69%) compared to earlier in pregnancy (38%) [2]. Research from Massachusetts General Hospital showed that at two months of age, 98% of infants born to vaccinated mothers had detectable anti-SARS-CoV-2 IgG; at six months, 57% still did [6]. This aligns with the Norwegian study's finding that protection wanes by the five- to six-month mark.

A question that researchers continue to study is whether high levels of maternal antibodies might blunt an infant's own immune response to later vaccinations — a phenomenon documented with other pathogens. Early evidence suggests some interference is possible, but the clinical significance remains unclear, and the consensus among immunologists is that the benefits of neonatal protection outweigh this theoretical concern [7].

Safety Data: Preterm Birth, Complications, and the Evidence Base

Multiple large studies have examined whether COVID-19 vaccination during pregnancy increases the risk of adverse obstetric outcomes.

A CDC analysis of over 40,000 pregnant women found no association between COVID-19 vaccination and preterm birth or small-for-gestational-age births, regardless of trimester or number of doses [8]. The New England Journal of Medicine published preliminary safety data in 2021 showing that rates of adverse pregnancy outcomes — including miscarriage (12.6%), preterm birth (9.4%), and small-for-gestational-age infants (3.2%) — among vaccinated pregnant people were comparable to pre-pandemic baseline rates [9]. No neonatal deaths were reported.

A systematic review in The Lancet Infectious Diseases confirmed that mRNA COVID-19 vaccination during pregnancy was not associated with increased risks of pregnancy loss, preterm birth, or congenital anomalies, including when administered in the first trimester [10].

Individual case reports and social media narratives have attributed various pregnancy complications to COVID-19 vaccination. Researchers note that observational studies cannot rule out every possible rare adverse event, but the consistency of findings across millions of vaccinated pregnancies globally provides strong reassurance. By contrast, COVID-19 infection itself during pregnancy is associated with significantly elevated risks of preeclampsia, preterm birth, and stillbirth [9].

The Policy Collision

The Norwegian study arrives at a moment of unusual tension between research findings and U.S. policy.

On May 27, 2025, HHS Secretary Robert F. Kennedy Jr. announced that the CDC would no longer recommend routine COVID-19 vaccination for healthy children and pregnant women [11]. "The COVID vaccine for healthy children and healthy pregnant women has been removed from the CDC recommended immunization schedule," Kennedy said in a video posted on social media [11]. The announcement was made alongside FDA Commissioner Dr. Marty Makary, bypassing the usual process of consultation with the CDC's Advisory Committee on Immunization Practices (ACIP) [11].

The decision drew sharp criticism from medical professionals. Dr. Thomas Nguyen, an obstetrician, said the Norwegian study "confirms that we were correct" in recommending vaccination during pregnancy [1]. The American College of Obstetricians and Gynecologists (ACOG) reaffirmed its recommendation for routine COVID-19 vaccination in pregnant individuals as recently as March 2026, calling it "standard preventive care" rather than something to be deferred to neutral shared decision-making [12].

An editorial in the New England Journal of Medicine described the revised recommendations as placing "U.S. vaccination policy under threat," arguing that the changes were not grounded in new safety or efficacy data but in political considerations [13].

Kennedy has a documented history of opposition to multiple vaccines. In 2021, he filed a citizen petition requesting that the FDA revoke COVID-19 vaccine authorization and described the vaccines as "the deadliest vaccine ever made" [11] — a claim not supported by safety monitoring data from the Vaccine Adverse Event Reporting System (VAERS), the Vaccine Safety Datalink, or international pharmacovigilance systems.

Vaccination Rates: Low and Falling

Even before the policy change, COVID-19 vaccination rates among pregnant people in the United States were well below those for other recommended maternal vaccines.

Source: CDC FluVaxView / COVIDVaxView

Data as of Mar 27, 2026CSV

CDC survey data from April 2024 showed that only 30.9% of pregnant women had received the updated 2023–24 COVID-19 vaccine, compared to 47.4% for influenza and 59.6% for Tdap (tetanus, diphtheria, and pertussis) [14]. By December 2024, uptake of the 2024–25 COVID-19 vaccine among pregnant women had fallen to just 13% [15].

Demographic breakdowns reveal disparities. Hispanic pregnant women had the highest COVID-19 vaccination rate at 38.6%, compared to 29.0% for Black women and 27.0% for White women [14]. For all three maternal vaccines, coverage was highest among women whose healthcare provider made a direct offer or referral (50.5%–76.1%) versus those who received no recommendation (0.3%–16.2%) [14]. Private insurance was associated with higher uptake across the board [14].

Globally, vaccine hesitancy among pregnant people is driven primarily by concerns about safety — specifically, fears about short- and long-term effects on the pregnancy and fetus [16]. A scoping review published in npj Vaccines found that lack of confidence in vaccine safety was the most prevalent theme, compounded by limited access to information and distrust of medical institutions [16]. Younger women (average age 28 versus 31 among vaccine-acceptant women) and those already hesitant toward other vaccines were more likely to decline COVID-19 vaccination [16].

The removal of the CDC recommendation is expected to further depress uptake, in part because insurance coverage for the vaccine may become less reliable without the backing of an official recommendation [11].

How COVID Vaccination Compares to Other Maternal Immunizations

Maternal immunization is not a new concept. Tdap vaccination during pregnancy has been recommended since 2012 to protect newborns against pertussis (whooping cough), and influenza vaccination during pregnancy has been standard practice for decades.

Research from the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP) estimates that maternal Tdap vaccination is 88.6% effective against pertussis-related hospitalizations or emergency department visits in infants, while maternal influenza vaccination is 69.7% effective against flu-related hospitalizations [17]. Maternal Tdap vaccination reduces the risk of pertussis in infants under two months by up to 78% and prevents severe cases in the first three months with over 90% efficacy [17].

By comparison, maternal COVID-19 vaccination effectiveness against infant hospitalization has ranged from 38% to 80%, depending on the variant in circulation and the timing of vaccination [2]. During the delta wave, effectiveness rivaled that of Tdap; during omicron, it was closer to the lower range of influenza vaccine effectiveness.

Maternal RSV vaccination, approved in 2023, has shown effectiveness of 68% or more against hospitalization, with protection reaching 82% in the first three months when administered between 32 and 36 weeks of gestation [17].

The pattern across all maternal vaccines is consistent: vaccination during pregnancy provides meaningful — sometimes substantial — protection to infants during their most vulnerable weeks, through the same mechanism of transplacental IgG transfer. Vaccinating household contacts after birth (known as "cocooning") offers some indirect protection by reducing the infant's exposure to circulating virus, but it does not provide the infant with their own circulating antibodies [7].

What Researchers and Clinicians Are Calling For

The researchers behind the Norwegian study and the broader body of evidence are largely aligned on policy recommendations.

ACOG continues to recommend COVID-19 vaccination as part of routine prenatal care, not as an optional discussion topic [12]. Dr. Kevin Ault, an expert in maternal immunization, stated that "one of the benefits of COVID vaccination during pregnancy is the passage of antibodies" that directly protect newborns [1].

Several researchers have called for COVID-19 vaccination to be formally added to pregnancy immunization schedules alongside Tdap and influenza vaccines. The WHO continues to recommend COVID-19 vaccination for pregnant individuals as a priority group, though specific scheduling guidance varies by country [18].

The timeline for any reversal of U.S. policy remains uncertain. ACIP, the independent advisory body that traditionally guides CDC vaccine recommendations, was sidelined in the May 2025 decision [11]. Whether the committee will revisit the issue — and whether its recommendations would be implemented under the current administration — is an open question.

In the meantime, state-level guidance varies. New York, for example, issued its own 2025–2026 COVID-19 immunization guidance for pregnant people, continuing to recommend vaccination regardless of the federal policy change [19].

The Broader Picture

The Norwegian study adds to a body of evidence that now spans millions of pregnancies across dozens of countries. The findings are consistent: COVID-19 vaccination during pregnancy reduces infant hospitalization, does not increase adverse pregnancy outcomes, and provides measurable protection during the months when infants are most vulnerable.

That this evidence is growing stronger at the same time the U.S. federal government has stepped back from recommending the vaccine presents pregnant individuals and their healthcare providers with a confusing landscape. The gap between the scientific literature and official U.S. guidance is wider now than at any point during the pandemic.

For clinicians, the message from professional societies is clear: continue recommending the vaccine. For patients, the decision increasingly depends on which source of authority they trust — their doctor, or the federal government.