Newborns get hepatitis B mainly during birth from an infected parent; close contact with infected blood at home can also spread HBV.
Hepatitis B is a blood-borne virus. For babies, the biggest risk is exposure to an infected parent’s blood and body fluids during labor and delivery. A small share of infections happen in the womb or during the first months at home through contact with infected blood. The good news: quick steps at birth and a complete vaccine series protect babies with high success rates.
Main ways a newborn gets hepatitis B
The routes below explain when transmission tends to occur and which factors raise the chance of infection. For clinical background, see the CDC perinatal hepatitis B overview and the WHO guidance on mother-to-child HBV transmission.
| How transmission happens | When it happens | What raises risk |
|---|---|---|
| Exposure to infected blood and fluids during labor and delivery | At birth | High HBV viral load, HBeAg positivity, delayed newborn prophylaxis |
| Transplacental or intrauterine exposure | Before birth (uncommon) | Placental leakage, acute infection late in pregnancy |
| Household contact with infected blood | Weeks to months after birth | Shared items that can cut skin, open cuts, bites that break skin |
During delivery: exposure to infected blood
Most newborn infections start while the baby is being born. Tiny breaks in skin or mucosa can let HBV in. The risk climbs when the parent has a high viral load or tests positive for the e antigen (HBeAg). Timely birth-dose vaccination and, when indicated, hepatitis B immune globulin (HBIG) cut this risk sharply.
Before birth: rare intrauterine infection
HBV can cross the placenta in a minority of pregnancies. This is more likely if a parent contracts HBV near the end of pregnancy or has marked viremia. Even in these cases, prompt newborn prophylaxis still lowers the chance of infection.
After birth: contact in the home
Infants can acquire HBV later through close contact with infected blood from a caregiver or relative. Examples include contact with blood from an open wound, a bite that draws blood, or sharing items that can break skin. Breastfeeding is allowed once the baby receives the birth-dose vaccine; take extra care if nipples are cracked or bleeding, as the CDC breastfeeding guidance explains.
Can a newborn get hepatitis B at birth? timing and risk
Yes. Birth is the main window for transmission. Without protection, a baby infected in the perinatal period faces a high chance of chronic HBV. Chronic infection can lead to liver disease years later. That is why prevention starts in pregnancy and continues through the infant vaccine series.
Why the perinatal window matters
Infants who acquire HBV have about a nine-in-ten chance of chronic infection. The younger the age at infection, the higher the chronic risk. This pattern drives the push for a fast birth dose and follow-up shots for every baby, not only those with known maternal infection.
How to cut the risk right away
The steps below keep transmission odds low. They apply whether delivery is vaginal or by cesarean.
Prenatal screening and planning
Every pregnancy should include an HBsAg test. If positive, clinicians usually check HBV DNA to gauge viral load. Many programs start tenofovir in late pregnancy for people with high viral load to lower exposure at delivery. The 2024 WHO hepatitis B guideline supports expanded eligibility for antiviral prophylaxis in pregnancy.
Immediate newborn prophylaxis
All infants should receive a dose of hepatitis B vaccine at birth. When the parent is HBsAg-positive or status is unknown, the baby should get HBIG along with the vaccine, ideally within 12 hours of life. This two-part approach acts as post-exposure protection.
Finish the vaccine series on schedule
After the birth dose, the series continues during early infancy. The exact timing can vary by product, birth weight, and local schedule, but the goal stays the same: complete all doses in the first months of life so protection is locked in.
Post-vaccination testing for exposed infants
Babies born to an HBsAg-positive parent need a blood test later to confirm they are protected and not infected. This test checks for surface antigen (HBsAg) and protective antibody (anti-HBs). Programs often schedule it between 9 and 12 months of age, after the series ends.
Which babies need HBIG at birth
HBIG is a ready-made antibody that gives immediate, short-term protection while the vaccine teaches the immune system to respond. Newborns with an HBsAg-positive parent should receive HBIG plus vaccine within 12 hours. If the parent’s status is unknown at delivery, hospitals give HBIG while the test is pending. When the parent later tests negative, the infant just follows the routine schedule. Preterm infants also receive special timing based on weight and product type; your team will chart the exact schedule.
Why viral load and HBeAg status matter
A high amount of virus in the blood makes transmission more likely during delivery. HBeAg positivity usually signals higher viral replication. In such cases, late-pregnancy antiviral therapy plus on-time infant prophylaxis lowers the chance that HBV will pass to the baby. These steps work together; neither replaces the other.
Breastfeeding with hepatitis B
Once the birth dose is given, breastfeeding can start. HBV does not spread through breast milk. If nipples are cracked or bleeding, pause on that side until healed to avoid contact with blood. Pediatric teams can help with latch and wound care while feeds continue on the other side or with pumped milk.
Household steps that lower exposure
Simple habits protect infants at home. Keep personal items that can break the skin off limits to others. Cover open cuts. Clean blood spills with a fresh bleach solution. Teach anyone who cares for the baby to use gloves when handling blood or body fluids. Relatives with HBV should stay in medical care and follow their treatment plan.
What if something was missed?
Late or missed birth dose
If the birth dose was delayed, give the first vaccine shot as soon as possible. For infants of HBsAg-positive parents, HBIG can still be given up to seven days after birth, though earlier is better. Resume the remaining doses on the catch-up schedule your clinic uses.
Unknown parental status at delivery
Hospitals should treat this as an exposure. That means the baby gets the vaccine within 12 hours and HBIG while the parent’s test is pending. If the parent later tests negative, the infant simply continues the routine series.
Concerns after a bite or blood contact
Wash the area with soap and water. If blood was involved and the source has HBV or status is unknown, call the baby’s clinician or an on-call service to plan next steps. A fully vaccinated infant has strong protection, yet timely advice is still wise after a blood exposure.
Clinic follow-up during the first year
After the hospital stay, routine visits keep HBV prevention on track. At early well-baby visits, teams check that the birth dose was given and schedule the next shots. They also review the parent’s HBV status in the chart so nothing gets lost between facilities. For infants exposed at birth, clinics place reminders to draw the post-vaccination blood test once the last dose is done and the child reaches the target age. If the antibody response is low, a repeat series or extra dose may be advised.
Newborn hepatitis B protection plan: what to do and when
Here is a quick timeline that families can use to track steps from delivery through the first year.
| Time point | What the baby should get | Notes |
|---|---|---|
| Within 12–24 hours of birth | Hepatitis B vaccine for all; HBIG if the parent is HBsAg-positive or status unknown | Give both in different thighs |
| 1–2 months | Second vaccine dose | Follow the product’s schedule |
| 6–18 months | Final vaccine dose | Age varies by product and local schedule |
| 9–12 months (if exposed at birth) | Blood test for HBsAg and anti-HBs | Confirms protection or detects infection |
Why universal newborn vaccination is standard
Not every pregnancy includes complete prenatal care. Some infections are new and may not show on early tests. Giving a birth-dose vaccine to every baby closes those gaps. Programs in many countries report sharp drops in infant HBV once the birth dose became routine.
When to talk to your clinician
Reach out if a dose was missed, if a needle or sharp object touched the baby, or if anyone in the home has HBV and the plan is unclear. Ask questions about antiviral therapy in late pregnancy, vaccine timing for preterm infants, and how to arrange the post-vaccination blood test. Clear steps keep stress low and keep protection on track.
Clear takeaways for parents
Know the plan
Ask your team to confirm HBV testing during pregnancy, note the result in the chart, and set a delivery plan. If you have HBV, ask about antiviral therapy in late pregnancy, the timing of HBIG, and the exact infant vaccine schedule.
Act fast at delivery
Make sure the birth dose is given on time. If HBIG is needed, it should be given with the vaccine in separate sites.
Finish the series and check protection
Put the later shots on your calendar. If the parent has HBV, plan the post-vaccination blood test during the first year.
When care teams and families follow these steps, newborns stay protected from a virus that can cause lifelong illness. That protection starts in the delivery room and continues through the first year. Stay prepared together.