CDC reaffirms safety of pandemic vaccine

Mar 23, 2010 (CIDRAP News) – As of mid February, about 86 million Americans had received the pandemic H1N1 vaccine, and so far no worrisome signals have emerged from extensive safety monitoring, officials from the US Centers for Disease Control and Prevention (CDC) said today at a conference call with heathcare practitioners.

In addition, Anthony Fiore, MD, a medical epidemiologist with the CDC's influenza branch, countered the view that the pandemic hasn't differed much from a normal flu season. He pointed out that pediatric deaths from the pandemic H1N1 virus tower high above past seasonal flu years, and showed that hospitalization rates in younger age-groups have been unusually high, and in older people unusually low.

Fiore added that one of the H1N1 pandemic's hallmarks is identification of newly recognized risk groups, such as those who are obese, children with neuromuscular conditions, and indigenous populations.

While no adverse event trends have emerged among those receiving vaccine, the CDC said it has seen some patterns with vaccine uptake. Fiore said most doses went to target groups, and coverage was higher in children than in adults. Of children under age 10 who received the vaccine, a group recommended to receive two doses, about 60% have gotten their second dose.

In adults, pandemic vaccine uptake was higher in whites than in blacks and Hispanics, though in children patterns did not vary by race or ethnicity, he said.

In analyzing uptake patterns, the CDC is identifying opportunities to refine its messages to the public, Fiore said. For example, a recent survey of adults found that the top reason for not getting the vaccine was that many didn't think they needed to be immunized.

The CDC has regularly posted brief pandemic H1N1 vaccine safety updates on its Web site, and in early December, 2 months into the immunization campaign, it published its first major report in Morbidity and Mortality Weekly Report (MMWR). Fiore said the CDC will publish another MMWR pandemic vaccine status report within the next few weeks.

Karen Broder, MD, from the CDC's immunization safety office, told clinicians that so far, the Vaccine Adverse Event Reporting System (VAERS), set up to detect possible signs of adverse events but not to verify a vaccine link, has shown that serious events related to the pandemic vaccine are no higher than with the seasonal flu vaccine, which has had an excellent safety profile.

As of Feb 16, serious events covered by the VAERS have been reported at a rate of 5.2 per million doses distributed. Reports submitted through the VAERS systems have gradually declined over the past months, mirroring the decline in vaccine doses distributed.

So far 46 VAERS reports involve fatalities, she said. According to a review of medical records, medical examiner reports for 22 of the patients listed cardiac causes of death.

As of Jan 31, medical chart reviews of VAERS reports verified Guillain-Barre syndrome (GBS) in 64 patients and anaphylaxis in 115 others. GBS is a rare side effect of the flu and other infections that was linked to a swine flu vaccine used by the United States in 1976. So far the rate appears to be below the US background rate for GBS, which is 1 case per 100,000 population.

Broder noted that on Feb 26 in a report to the Food and Drug Administration's National Vaccine Advisory Committee, the CDC's nongovernmental vaccine safety working group said it had enough data to detect adverse events and that it had so far found no connection to adverse event patterns and the pandemic H1N1 vaccine. The working group was set up to independently evaluate and synthesize H1N1 vaccine data.

She thanked clinicians for their role in stocking and storing the vaccine, screening and educating patients, administering the vaccine, and submitting VAERS reports. "This is not a small task. You have a lot of responsibility, and we appreciate your efforts," Broder said.

See also:

CDC clinicians conference call information

Dec 4, 2009, CIDRAP News story "CDC heartened by initial safety reports on H1N1 vaccine"

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