"Compared to childhood vaccines, people would [probably] think 55% is not too impressive, because many childhood vaccines are in the range of 80% to 90% [effective]," says researcher Hung Fu Tseng, PhD, MPH, a research scientist at Kaiser Permanente Southern California.
However, he tells WebMD, the 55% risk reduction ''is pretty high compared to other adult vaccines."
Getting the vaccine makes it less likely that adults will get the painful rash that can occur when the varicella zoster virus, which causes childhood chickenpox, reactivates to cause shingles. The associated pain can last months or even years.
About a million episodes of shingles, sometimes debilitating, occur in the U.S. annually, Tseng says.
The new study is published in the Journal of the American Medical Association.
Another new study, published in the American Journal of Preventive Medicine, finds that by 2008, less than 7% of U.S. adults aged 60 and older had gotten the vaccine, which has been available just since 2006.
Called Zostavax, the shingles vaccine is made by Merck.
Shingles Vaccine: The Numbers
Tseng and his colleagues evaluated the risk of shingles in 75,761 members of the Kaiser Permanente Southern California health plan who got the vaccine from Jan. 1, 2007, through Dec. 31, 2009, and the risk in another 227,283 health plan members in the same age brackets who did not get the vaccine.
- Among those vaccinated, there were 6.4 cases per 1,000 people per year.
- Among those not vaccinated, there were 13 cases per 1,000 people per year.
The risk reduction was similar in men and women and in different racial groups, the researchers found, and in people who had chronic diseases such as diabetes.
Certain people should not get the vaccine, Tseng says, including people with a compromised immune system and certain cancers.
In a previous study, side effects were minor, such as redness and pain at the injection site.
The new study was funded internally by Kaiser, but Tseng reports getting research funding from Merck for previous vaccine research.