In the United States, only one vaccine is given at birth: the first dose of the hepatitis B vaccine. It’s typically administered within the first 24 hours of life, before a newborn leaves the hospital. Your baby will also receive a vitamin K injection shortly after delivery, but that’s a nutrient, not a vaccine, even though it looks the same.
If you’re reading from outside the U.S., the picture is different. Many countries give additional vaccines at birth, including one for tuberculosis and one for polio. The details depend on where you live and what diseases are common in your region.
Why Hepatitis B Is Given So Early
Hepatitis B is a viral infection that attacks the liver. Adults who catch it usually fight it off, but babies are different. When a newborn is infected, the virus is far more likely to become a lifelong chronic infection that can lead to liver damage or liver cancer decades later. The birth dose works by training the baby’s immune system to recognize a protein on the surface of the virus, building protection before any potential exposure can take hold.
The timing matters most when a mother carries the virus, sometimes without knowing it. The birth dose alone reduces mother-to-child transmission by roughly 70%. When combined with a separate protective antibody injection given to high-risk newborns, that protection rises to 83% to 97%. But because not all infected mothers are identified during pregnancy, the CDC recommends the vaccine for every newborn regardless of the mother’s status. This universal approach catches cases that would otherwise slip through.
What Happens If the Mother Has Hepatitis B
If a mother tests positive for hepatitis B (or her status is unknown at the time of delivery), her baby receives both the vaccine and a dose of hepatitis B immune globulin, which provides immediate, temporary protection. Both are given as separate injections in different limbs within 12 hours of birth. This combination is the most effective way to prevent the virus from passing to the baby during delivery.
If the immune globulin is missed in those first 12 hours, it can still be given up to 7 days after birth. Beyond that window, it’s unlikely to be effective.
Adjustments for Premature or Low-Weight Babies
Babies born weighing less than about 4.4 pounds (2,000 grams) respond less strongly to the vaccine, so the timing may shift depending on the mother’s hepatitis B status. If the mother is negative, the birth dose is typically delayed until the baby reaches 1 month of age or is discharged from the hospital, whichever comes first. That first dose then “restarts” the series rather than counting toward it.
If the mother is positive or her status is unknown, the baby receives both the vaccine and immune globulin within 12 hours of birth regardless of weight. In this situation, the risk of infection outweighs the concern about a slightly weaker immune response.
Side Effects in Newborns
The hepatitis B vaccine is one of the most studied vaccines given to newborns. The most common reactions are mild: soreness at the injection site, slight fussiness, or a low-grade fever. Some infants may have brief changes in appetite or sleep patterns.
Severe allergic reactions are possible but extremely rare. A large CDC review of over 20,000 adverse event reports filed between 2005 and 2015 found that the most frequently reported issues were fever, redness at the injection site, and vomiting, and the vast majority of these occurred when hepatitis B was given alongside other vaccines at later visits rather than at birth alone. A separate study comparing vaccinated and unvaccinated newborns found no difference in death rates, fevers, or suspected infections. The largest case series review of hepatitis B vaccine reports among newborns found no serious health problems linked to the vaccine.
When the Vaccine Would Be Delayed
There are very few reasons to skip or delay the birth dose. The two recognized contraindications are a severe allergic reaction to a previous dose (relevant only if a baby somehow already received one) and a known hypersensitivity to yeast, since yeast is used in the manufacturing process. If a newborn has a moderate or severe acute illness at the time of birth, the vaccine may be deferred until the baby stabilizes.
Birth Vaccines Outside the United States
The U.S. schedule is unusually minimal at birth compared to much of the world. Over 150 countries include the BCG vaccine (which protects against tuberculosis) in their birth-dose schedule. This list spans most of Africa, South Asia, Southeast Asia, and Latin America, as well as parts of Eastern Europe and the Middle East. Countries like India, Brazil, China, South Africa, and the Philippines all administer BCG at birth.
Many of these same countries also give a dose of oral polio vaccine at birth, particularly in regions where polio has not yet been fully eliminated. The U.S. and most of Western Europe dropped both BCG and birth-dose polio from their schedules because the diseases became rare enough domestically that the benefit no longer justified routine use. If you’re traveling internationally with a newborn or living abroad, your baby’s birth vaccines may look quite different from the standard U.S. list.
What Comes After the Birth Dose
The hepatitis B vaccine given at birth is just the first in a series. Your baby will need a second dose at 1 month of age and a third dose between 6 and 18 months to complete the series and build lasting immunity. The next round of new vaccines, covering diseases like rotavirus, diphtheria, whooping cough, and pneumococcal disease, begins at the 2-month visit. The birth dose is the only vaccine your newborn receives before that point.