christopher labos: why we vaccinate babies against hepatitis b

given the rising number of measles cases, being up to date with your immunizations (it takes two doses for measles) is very important.but there are always questions from concerned parents, including a few raised in a recent letter to my editors, and this seems like a good opportunity to provide some answers.first off, why do we vaccinate babies against hepatitis b?there is a common perception that hepatitis b is a disease of adults, transmitted via sexual intercourse or needles. if that were the case, vaccinating babies would be nonsensical.but the reality is that hepatitis b is a disease that affects many infants and young children worldwide. and unfortunately, the younger you get the virus, the more likely it is to become a chronic infection that can cause cirrhosis or liver cancer. while most diseases are more severe if you get them as an adult, hepatitis b is paradoxically worse if you get it young. infants less than one year old who get hepatitis b have an 80-90 per cent chance of developing a chronic infection, compared to 30-50 per cent of children under 6 and less than 5 per cent of adults.hepatitis b is one of three main hepatitis viruses that are clinically important in north america: hepatitis a, b and c. there is actually a hepatitis d and a hepatitis e as well, but hepatitis d is a strange virus that requires you to be infected with hepatitis b before it can infect you. hepatitis e is very similar to hepatitis a, but found mostly in east and south asia. hepatitis a is usually transmitted via contaminated food or water and is generally (but not always) a short-lived infection. hepatitis b and c are harder for the immune system to clear and can develop into chronic infections that cause liver failure.between 1990 (about the time when universal hepatitis b vaccinations started) and 2006, the rate of hepatitis b infection fell by 81 per cent to the lowest level ever recorded, and the decline was greatest among children. today, most hepatitis b infections in north america occur in adults. but worldwide, in places where hepatitis b is still common, infections can and do occur very frequently in children.which raises the question of how children and infants can be infected if hepatitis b is spread through sex and dirty needles. here, too, we have forgotten our history. although less frequently seen in north american now, worldwide one of the most common methods of hepatitis b spread is from pregnant mothers to their babies at the time of birth. also, while hepatitis b is an infection that lives in bodily fluids, it can survive outside the human body for several days, which means that sharing contaminated household products is a possible source of infection.in the end, there is a very simple answer to the question of why we vaccinate babies against hepatitis b. universal vaccination programs against hepatitis b have resulted in drastic reductions in hepatitis b cases in north america. unfortunately, in the rest of the world, where resources are scare and vaccines are not widely available, hepatitis b remains a huge problem.the hepatitis b vaccine, like many other vaccines, is a victim of its own success. it has led to such drastic reductions in infections that we no longer see hepatitis b as a threat. we don’t see hepatitis infections as much anymore, but if we stop vaccinating our children, we will.christopher labos is a montreal doctor and an associate with the mcgill office for science and society. he also co-hosts a podcast called the body of evidence.