The hepatitis B vaccine is a shot that trains your immune system to fight off the hepatitis B virus, a infection that can cause serious liver damage, liver cancer, and liver failure. It works by exposing your body to a single protein from the virus’s outer surface, not the virus itself, so there’s no risk of infection from the vaccine. Over 90% of healthy adults who complete the full series develop protective immunity, and that protection lasts at least 30 years when vaccination starts in infancy.
How the Vaccine Works
The hepatitis B virus has a protein on its outer shell called hepatitis B surface antigen, or HBsAg. Rather than using any part of the live virus, vaccine manufacturers take the gene responsible for producing that surface protein and insert it into common baker’s yeast. The yeast cells then grow in large cultures and churn out copies of the protein, which is harvested, purified, and combined with an aluminum-based compound that boosts your immune response.
When injected, this harmless protein fragment is enough to alert your immune system. Your body produces antibodies specifically designed to recognize and neutralize the real virus if you’re ever exposed. An antibody level above 10 mIU/mL in your blood is the recognized threshold for protection. Because the vaccine contains only a single viral protein grown in yeast, not a weakened or killed virus, it cannot cause hepatitis B infection.
Vaccines Currently Available
Several hepatitis B vaccines are on the market, and they differ in their ingredients, dose count, and target age groups.
- Engerix-B and Recombivax HB are the traditional options, both using aluminum as an immune-boosting ingredient. They require three doses given at 0, 1, and 6 months and are approved for all ages, including newborns.
- Heplisav-B uses a different immune-boosting ingredient derived from synthetic bacterial DNA instead of aluminum. The key advantage: it requires only two doses, given one month apart, making it easier to complete. It’s approved for adults 18 and older.
- PreHevbrio contains three viral surface proteins instead of just one, which may produce a broader immune response. It follows a three-dose schedule at 0, 1, and 6 months, is approved for adults 18 and older, and is the only hepatitis B vaccine that does not contain yeast. That makes it a safe option for people with yeast allergies.
For adults who have trouble responding to standard vaccines, such as those over 45, people living with HIV, or those with kidney disease, PreHevbrio has shown consistent immune responses across these groups. A two-dose schedule of PreHevbrio has been enough to achieve protective antibody levels in over 95% of recipients in studies.
Who Should Get Vaccinated
The CDC recommends hepatitis B vaccination for all infants starting at birth and for all unvaccinated people through age 19. For adults, the recommendation is now universal for those aged 19 through 59, with vaccination also recommended for adults 60 and older who have risk factors or simply want protection.
Infants born to mothers who test positive for the virus receive the vaccine along with a separate injection of hepatitis B immune globulin, which provides immediate, temporary protection while the baby’s own immune response builds. Babies weighing at least 2,000 grams (about 4.4 pounds) should receive their first dose within 24 hours of birth. Smaller newborns get their first dose at one month of age or when they leave the hospital, whichever comes first.
The Standard Dosing Schedule
For infants, the routine schedule is three doses: one at birth, one at 1 to 2 months, and a final dose between 6 and 18 months. The last dose should not be given before 24 weeks of age. If a combination vaccine that includes hepatitis B is used after the birth dose, your child may end up receiving four total doses, which is safe and acceptable.
Adults getting vaccinated for the first time can choose between a three-dose series (at 0, 1, and 6 months) with the traditional vaccines, or a two-dose series one month apart with Heplisav-B. The two-dose option is particularly useful for people who might not return for a third appointment.
How Effective It Is
More than 90% of healthy adults develop protective antibody levels after completing the full series. Among healthy people vaccinated in infancy, immunity persists for at least 30 years.
The picture is somewhat different for higher-risk groups. In a study of 640 children born to infected mothers, protective antibody levels dropped from 93% shortly after vaccination to 70% at 5 years, 40% at 10 years, and 25% at 15 years. This decline in measurable antibodies doesn’t necessarily mean those individuals are unprotected, though. The immune system retains memory cells that can mount a rapid response if the virus is encountered, even when antibody levels have fallen below the detectable threshold. About 90% of people still show evidence of protection 30 years after their primary series, suggesting that immune memory fills the gap as circulating antibodies fade.
A small percentage of people, roughly 5%, don’t respond adequately to the initial series. For infants born to infected mothers, the failure rate ranges from about 2% when tested shortly after vaccination to nearly 22% when tested over a year later, reflecting that natural antibody decline rather than true immune failure.
Side Effects
The hepatitis B vaccine has been in use for decades and has a well-established safety profile. The most common side effects are mild and local: soreness, redness, or swelling at the injection site. Some people experience a low-grade fever or fatigue for a day or two. Severe allergic reactions are extremely rare.
The main contraindication is a known allergy to yeast, since most formulations are produced using baker’s yeast and may contain trace amounts (less than 1% yeast protein per dose). If you have a yeast allergy, PreHevbrio is the one option manufactured without yeast. A severe allergic reaction to a previous dose of any hepatitis B vaccine is also a reason to avoid further doses of that same product.
Checking Your Immunity
If you were vaccinated years ago and want to know whether you’re still protected, a simple blood test can measure your antibody level. A result above 10 mIU/mL confirms you have protective immunity. This testing is particularly relevant for healthcare workers, people with ongoing exposure risk, and those with weakened immune systems who may not have responded fully to the original series. If your levels have dropped below the threshold, a booster dose or revaccination series can restore protection.