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.