I believe it is very common. Anyone who is not immunized against Hep B is neglecting their health. 

A blood test will let you know if your hep B shots are still effective

Dont take a chance. Get immunized.

Hepatitis B is indeed very common in China,  And it is very good advise to get the proper vaccination prior to coming to China, and do keep it renewed as recommended if necessary.  And here, not only it is a very common sickness, but "carries" face discrimination at their work place and neighborhood once it becomes public that he or she is infested.

In China, however, discrimination against people who carry the hepatitis B virus is not only possible but widespread. Even though at least 10 percent of the Chinese population carries the virus, which can attack the liver and cause lifelong infection, cirrhosis or liver cancer, there is a failure among many to understand that it cannot spread through casual contact.

Experts say the barriers faced by people with the virus fit into a larger context of job discrimination in China, where labor laws are not enforced or are contradictory. Institutions such as universities and the Foreign Ministry are said to discriminate against applicants based on height -- they prefer taller candidates -- while private employers routinely push middle-age women to retire early in favor of younger, cheaper employees, for example.

A 13-year-old labor law prohibits discrimination on the basis of ethnicity, race, sex or religious beliefs, but the regulation is too vague to be of use, experts say. In a survey of more than 3,000 people in 10 cities, results of which were published last month by the Beijing Morning Post, 85 percent of respondents said they believed there was discrimination in the workplace.

In the case of hepatitis B, experts say, discrimination is on the increase, partly because the dangers of the virus have been exaggerated by medical testing companies touting services and advertisers pushing fake cures. Such ploys gain attention in China, where 120 million carry the hepatitis B virus.

The virus is transmitted in body fluids, primarily blood and semen, but occasionally saliva as well. About 90 percent of people infected at birth, and about 10 percent infected later, become carriers, able to infect others for years. Many Chinese were infected by needles that were reused during mass vaccination programs for tuberculosis, tetanus and encephalitis from the 1970s to the 1990s.

Although many carriers have no symptoms, at least one-quarter will ultimately suffer some complication from the infection.

In the southern parts of China, it is especially dangerous. You should have both the Hep. A and B shot. It's not an investment, it's your life.

how often do you need to renew hepatitis shots?

Hepatitis B is a series of three shots spaced over a few months time, exactly when I do not recall.  But it is also important to have a blood test to see if they were successful and you are really immune or not.  If you are, for some people it will last a lifetime, no need for booster shots.  

But after a few years, it is advisable to renew the blood test to check immunity levels, and if low, then a booster shot should be required.

Along with what happy said, typically every two years. They do a liver test for antibodies and the ability to fight off Hep. Some people actually do not need the shots for the antibodies in their blood have the ability to fight off the disease but they can still be carriers, this is why even though I was told I didn't need the shot, I got it anyway.