What are the symptoms and how does hepatitis B progress?

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It is helpful to think of two phases of infection with hepatitis B virus. An acute phase when you are first infected, and a chronic (persistent) phase when the virus remains long-term in some cases.

Acute infection

Acute means 'new' or 'for a short time'. Symptoms of acute hepatitis may develop shortly after you first become infected with the virus (within 1-6 months which is the 'inclubation period'). Symptoms include: feeling sick, vomiting, abdominal pains, fever, and feeling generally unwell. Some people become jaundiced (go 'yellow'). This is due to a build up of the chemical bilirubin which is made in the liver and spills into the blood in some liver conditions. (With jaundice due to hepatitis your urine goes dark, your faeces (stools) may go pale, and and you tend to itch.)

Symptoms of acute hepatitis B infection usually go after a few weeks as the immune system either clears the virus, or brings it under control. Rarely, an acute severe ('fulminant') hepatitis develops which is life-threatening.

However, in about half of cases, no symptoms or only mild 'flu-like' symptoms develop in the acute phase. You may not be aware that you have been infected with hepatitis B. In particular, babies who are infected from their mothers during childbirth usually have no symptoms at first.

Following the initial 'acute' phase:

In more than 9 in 10 cases in adults, the virus is cleared from the body by the immune system within 3-6 months. In this situation you are no longer infectious and you are immune to further infection.
In up to 1 in 10 cases in adults, the virus remains long-term ('chronic hepatitis B infection'). This may occur whether or not you have symptoms in the acute phase.
In more than 9 in 10 babies infected from their mothers, the virus remains long-term.

So, in other words, there is a good chance of full recovery and clearing the virus for adults who become infected with hepatitis B, but not so for new-born babies who become infected.