The report also found that both expired and unexpired vaccines had been stored together in some doctors' offices and clinics, which could potentially lead to mistakes in giving the wrong version, the Office of the Inspector General (OIG) in the Department of Health and Human Services said.

The findings could apply to a much wider lot of vaccines, since many of the same clinics that provide free immunizations for low-income children also give shots to insured children.

"We do know that vaccines exposed to temperatures that are too warm, too cold, or past the expiration date, may not provide maximum protection against disease," Holly Williams, a program analyst in the OIG's office, said in a podcast interview posted online. She added that the vaccines are still safe.

The OIG visited 45 medical practices from the five areas that ordered the most vaccines in 2010: California, Florida, Georgia, New York City and Texas. Together, they accounted for 36 percent of all vaccine orders that year.

The inspectors found 76 percent of the offices or clinics had stored vaccines at the wrong temperature for at least five hours in a row during a two-week period. These improperly stored vaccines were worth nearly $370,000.

The study also found 13 of the 45 providers mixed expired and unexpired vaccines, and 16 of them kept expired vaccines.

Since 1994, the Centers for Disease Control and Prevention (CDC) has been providing free vaccines to children when parents cannot afford them or do not have insurance. The Vaccines for Children program spent $3.6 billion in 2010 to give 82 million vaccines to some 40 million children.

The federal government gives grants to state or local health departments, who then distribute the vaccine funds to 44,000 doctors' offices and clinics.

None of the providers managed vaccines according to all the program's rules, or had the proper documentation. And none of the five state or city agencies that gave the grants met all the oversight rules.

The CDC agreed to work with clinics and states to make sure the vaccines are better managed, and said the United States still has one of the best vaccination rates in the world, with 90 percent or greater reduction in preventable diseases.

The CDC said its efforts could help vaccine management in general, since 90 percent of U.S. children are vaccinated by medical practices that participate in the Vaccines for Children program.

Vaccines from companies including Sanofi SA, Merck & Co Inc and GlaxoSmithKline PLC provide protection against communicable diseases such as diphtheria, tetanus, measles and meningococcal disease.

(Reporting by Anna Yukhananov, Editing by Maureen Bavdek)

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