A July 30 article incorrectly said that thimerosal, a compound used to preserve some vaccines in multi-dose vials, contains "a minute amount of mercury." Thimerosal contains about 50 percent mercury by weight. Childhood vaccines in the past contained a small amount of thimerosal, and current formulations contain smaller amounts or none.

The article also said that the National Academy of Sciences' Institute of Medicine "reviewed the evidence for the compound's hazards and found none." The institute's report in May concluded that "the body of epidemiological evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism" and that the "potential biological mechanisms for vaccine-induced autism . . . generated to date are theoretical only." (Published 9/17/04)

Immunization of infants and toddlers in the United States reached an all-time high last year, with nearly 80 percent of children vaccinated against nine diseases before their third birthdays.

Immunization rates have risen steadily since 1999, and increased nearly 5 percent -- an unusually large jump -- in 2003, according to data released yesterday by the Centers for Disease Control and Prevention. The trend suggests that vaccine skeptics, whose views have led to significant decline in immunization rates in Britain, have had little practical effect here.

Rates varied geographically, with lower levels in the West than the East, and lower in big cities than in states as a whole. Overall, 79 percent of children younger than 3 had received the basic schedule of vaccines. In the District, the rate was 76 percent; in Maryland, 81 percent; and in Virginia, 84 percent. The highest rate -- 94 percent -- was in Connecticut. For reasons that baffle CDC epidemiologists, Colorado had the lowest rate, 68 percent.

The CDC estimates that childhood immunization prevents 10.5 million cases of illness and 35,000 deaths a year. Nevertheless, there are about 1 million American children who are not fully immunized, Julie L. Gerberding, the CDC director, said at a news conference here.

"This is the record year . . . but we still have challenges in protecting children from these devastating diseases," she said.

The rates announced yesterday covered vaccination against diphtheria, pertussis, tetanus, measles, mumps, rubella, Haemophilus influenza Type B, polio and hepatitis B. They did not include two recently introduced vaccines -- varicella (chickenpox) and pneumococcal conjugate.

Those new shots, however, are rapidly gaining acceptance, with 85 percent of children vaccinated in 2003 against chickenpox and 68 percent against pneumococcal bacteria (which cause ear infections, pneumonia and meningitis).

The U.S. rates are below those of most Western European countries. In Scandinavia, more than 95 percent of children are fully immunized by age 3. The U.S. rates climb above 90 percent by the time children enter school.

"Our problem in the United States is getting those high coverage rates on time," said Stephen L. Cochi, acting director of the CDC's National Immunization Program.

Vaccination against measles, a viral infection that kills about 745,000 children each year worldwide, is falling in Britain because of fears that the measles-mumps-rubella vaccine causes autism, a devastating neurological condition marked by extreme social isolation and lack of emotion. British MMR coverage was 92 percent in 1996, but by 2002 it had fallen to 84 percent. Measles cases rose from about 100 to about 300 a year over that period.

Research has refuted a link between MMR use and autism. Some people, however, have pointed to another vaccine component -- a preservative called thimerosal that is put into multiple-dose vials -- as the cause of autism's apparent rising incidence.

Thimerosal contains a minute amount of mercury, a metal that can cause neurological damage at much higher doses. A recent report by the National Academy of Sciences' Institute of Medicine reviewed the evidence for the compound's hazards and found none.

Despite the apparent confidence of American parents in childhood vaccines, Cochi said that "we remain concerned [about] a rising curve of shrill misinformation on the part of the anti-vaccine movement."

CDC officials also urged yesterday that children age 6 months to 23 months get an influenza vaccination each winter. At least 152 children died of that infection last flu season.

About 8 million children fall into that age group each flu season. Unlike adults, they require two flu shots, a month apart, to be protected.

A vaccine manufacturer is making a limited amount of thimerosal-free flu vaccine -- preloaded into syringes, at a higher cost -- to allay parents' fears about that substance. CDC has bought 3 million doses of that vaccine for immediate distribution and will put 2.5 million in a stockpile.

About 100 million doses of flu vaccine will be available in the coming winter, compared with 86.9 million last winter.

Also at yesterday's news conference was a victim of a rare but devastating vaccine-preventable disease -- meningococcal meningitis.

John Kach, 23, contracted the infection during his freshman year at a college in Rhode Island. He developed sepsis, nearly died and ultimately required the amputation of his fingers and both legs below the knee.

He said he had intended to get the meningitis vaccine, which costs about $80, but never got around to it. The vaccine is recommended for college students, military recruits and other young adults living in close quarters.

"All I went through could have been prevented for [the cost] of a pair of sneakers," he said.