Deaths from chickenpox, although rare, have dipped steeply after the U.S. began vaccinating against the virus in 1995, a new government report concludes.
Since the early 1990s, the bug has gone from killing 105 a year to causing fewer than 20 annual deaths between 2003 and 2007.
Writing in the journal Pediatrics, researchers from the Centers for Disease Control and Prevention (CDC) call the results "impressive" and say they show the benefit from the vaccine program is larger than expected.
Chickenpox is caused by the varicella zoster virus and produces fever and an itchy rash. In rare cases, it can be complicated by bacterial infections, swelling of the brain or pneumonia.
Before vaccination became mandated, a few million Americans caught the infection every year. Although most cases are mild, thousands of people landed in the hospital due to the disease.
Now, the number of people who get infected has been cut dramatically. The CDC's new report, which updates an earlier analysis from 1995 to 2001, shows deaths have dropped by as much as 88 percent over the first 12 years since the varicella vaccine was introduced.
That's a decline from 0.41 to 0.05 annual deaths per one million Americans between the early 1990s to the mid-2000s.
The varicella vaccine is mandated in all states, and in 2006 the dose was upped from one to two shots, which researchers say give better protection.
About a fifth of infants get some swelling and soreness around the injection site, and 10 percent also experience passing fever. Fewer than one in 1,000 of those who get the shot also develop a seizure from the fever, although experts say it's usually harmless.
Varivax, a varicella vaccine developed by Merck, costs about $84 per dose, but the new report says the vaccination program has exceeded expectations in terms of cost-effectiveness.
"Our analysis documents the impressive impact on varicella mortality of the US vaccination program, largely during a period when only 1 dose was administered," the researchers conclude.
"With the current 2-dose program, there is potential that these most severe outcomes of a vaccine-preventable disease could be eliminated."