A new modeling study estimates that moving the hepatitis B vaccine from a birth dose to a later start could mean more chronic infections in children: 255 cases per birth cohort under universal birth-dose vaccination, versus 303 if the first dose is delayed to 2 months and 467 under shared decision-making with an assumed 50% uptake. The study, published in Annals of Internal Medicine and announced by Mass General Brigham on Oct. 19, is a projection, not a count of real cases. Here is what it found, what it cannot tell us, and what parents can ask. This is general information, not medical advice.
What the new hepatitis B vaccine study found
The paper is titled “Projected Effect of 2026 Federal Changes to the Childhood Immunization Schedule on Chronic Hepatitis B Virus Infections in the United States.” The corresponding author is Amir Mohareb, MD, of the Mass General Brigham Center for Global Health. Ravi Jhaveri is among the other authors, according to the release.
The team built a computer model, described as a Markov cohort state-transition model. It follows 3.6 million people, one year of U.S. births, through the first 20 years of life. The researchers said they validated it against CDC estimates of pediatric infections.
Funding came from the National Institute of Allergy and Infectious Diseases (NIAID), an MGH Research Scholar Award and the Harvard Center for AIDS Research (CFAR), per the release.
The model compared three scenarios. In all three, infants born to mothers who test positive for hepatitis B virus (HBV) are still assumed to be vaccinated.
- Universal birth dose (baseline): every newborn gets the first hepatitis B vaccine dose shortly after birth.
- Delay to 2 months: infants of mothers without HBV wait until age 2 months, reflecting the ACIP recommendation of December 2025.
- Shared clinical decision-making: families and clinicians decide together, with an assumed 50% of children vaccinated at 2 months or older, reflecting the CDC’s 2026 approach.
The numbers: 255, 303 and 467 chronic infections
Here is how the modeled results compare, as reported by Mass General Brigham.
| Scenario | Chronic HBV infections | Change vs. baseline | Susceptible adults at age 20 |
|---|---|---|---|
| Universal birth dose | 255 | Baseline | 232,000 |
| Delay to age 2 months | 303 | About 19% more | About 474,000 |
| Shared decision-making (50% assumed) | 467 | About 83% more | About 1.8 million |
Put simply, the model projects that changing the hepatitis B vaccine timing could add roughly 48 more chronic infections in a delayed-dose scenario and about 212 more under shared decision-making, compared with the baseline. Those differences come from our subtraction of the reported figures, so treat them as approximate.
TIME reported a separate figure. If only about 26% of children were vaccinated, which it described as the estimated rate under shared decision-making, chronic cases would rise 225%. TIME’s report does not clearly state the baseline for that number, so we are noting it with that caveat rather than treating it as a headline result.
Mohareb said in the release: “Even a small increase in childhood HBV infections could have large clinical, public health, and economic effects.” He also told TIME: “Imagine that happening year after year after year after year.”
Why newborns get a birth dose
Hepatitis B is a virus that attacks the liver. For adults, many infections clear. For infants, the picture is different. TIME, citing public health sources, reported that up to 90% of babies infected before age 1 go on to develop chronic infection, and that early-life infection carries a 1 in 4 lifetime chance of liver cancer. Those are TIME’s attributions, and we have not independently verified them.
The U.S. began routine infant hepatitis B vaccination in 1991, according to TIME. The hepatitis B vaccine birth dose is designed to protect babies in the first hours and days of life, including when a mother’s infection status is unknown or was missed.
The CDC has long used its hepatitis B information pages to explain how the virus spreads and why screening during pregnancy matters. Parents can find the current agency guidance there.
Who recommends what on the newborn hepatitis B vaccine
The recommendations now differ by organization, so it helps to separate them. Here is the policy background as reported by Mass General Brigham and TIME.
- Before December 2025: the CDC recommended a universal hepatitis B vaccine birth dose.
- December 2025: the Advisory Committee on Immunization Practices (ACIP) recommended delaying the first dose until at least 2 months for infants of mothers without HBV.
- 2026 CDC approach on the hepatitis B vaccine: shared clinical decision-making, with the first dose “no earlier than 2 months” as an option. For babies whose mothers test positive, or whose status is unknown, the CDC still recommends a dose shortly after birth.
- American Academy of Pediatrics (AAP): still recommends a birth dose for all infants, per TIME.
- Legal action: TIME reported that 15 states sued over the schedule changes.
We are reporting who recommends what, not taking a side. Families who want the pediatric perspective can read the AAP’s parent-facing site, HealthyChildren.org.
What the study cannot tell us
A model of the hepatitis B vaccine schedule is only as good as its assumptions. This one deserves a careful read, because the headline percentages can sound more certain than they are.
- The 50% uptake is an assumption. It is a scenario input, not an observed vaccination rate.
- It models one birth cohort. The 3.6 million figure represents a single year of U.S. births, followed for 20 years.
- No deaths or liver cancer counts. The release reports chronic infections and susceptible adults, not downstream outcomes such as liver cancer cases.
- It is a projection. Real-world vaccination rates, screening practices and follow-up could differ from what the model assumes.
The hepatitis B vaccine numbers are also small relative to 3.6 million people. Mohareb’s point, as quoted above, is that even small annual increases could add up over time. Whether that concern is borne out will depend on what families and clinicians actually do, and that is not yet known.
We also do not have the full paper’s methods in our reporting, only the Mass General Brigham release and TIME’s coverage. Readers who want the details can go to the Mass General Brigham release and the study itself.
What parents can ask about the hepatitis B vaccine
If you are expecting a baby or have a newborn or toddler, these conversations are practical and low-pressure. They are not a substitute for your own clinician’s advice.
- Ask your OB about your hepatitis B test result. Find out whether you were tested during pregnancy and what the result was. Ask that it be shared with your baby’s hospital team and pediatrician.
- Ask about the hepatitis B vaccine birth dose. Ask your pediatrician and the hospital what they recommend for your baby and why, given your situation.
- Ask for the full schedule. The hepatitis B vaccine is given as a series of doses. Ask when each is due so nothing slips.
- Keep your records. Take a photo of your baby’s immunization record and bring it to every visit.
- Do not delay care. If you are unsure about the hepatitis B vaccine or any other shot, schedule the conversation early rather than skipping well-child visits.
- Check trusted pages. Compare what the CDC and the AAP say, and bring questions to your pediatrician.
Hepatitis B is one of several vaccine topics families are weighing this fall. Our reports on measles cases topping 4,000 and the 2026-27 flu vaccine checklist for kids cover other items worth putting on your list.
What is not yet known
Several questions remain open. We do not know how many families will choose a later first dose, so the 50% assumption could prove too high or too low. We do not know how hospitals will change their routines. And we do not know how the legal challenges by 15 states will end.
The study also does not say how the hepatitis B vaccine timing affects what any individual baby’s risk is. That depends on a mother’s test result, household exposures and other factors that only a clinician can weigh.
The bottom line
The new analysis projects that delaying the hepatitis B vaccine for newborns would lead to more chronic infections over time: 303 or 467 per birth cohort, versus 255 under a universal birth dose. It is a model with stated assumptions, and recommendations now differ between the CDC, ACIP and the AAP.
Your takeaway: find out your own hepatitis B test result, ask your pediatrician about the birth dose and the full schedule, and keep your baby’s records current. Stay with USA One News for updates as more research and guidance arrive.
