Pandemic Flu Vaccines Comparably Safe

Vaccines for pandemic influenza appear to be as safe as current seasonal influenza vaccines, reports the CDC. The Center's preliminary assessment of safety reports from the US Vaccine Adverse Events Reporting System (VAERS) and the Vaccine Safety Datalink (VSD) are available in the latest issue of the MMWR.

Data from VAERS*—which includes publicly volunteered information—reveal overall adverse-event (AE) rates of 82 per 1 million doses of pandemic flu vaccine (0.0082%) and 47 per 1 million doses of seasonal flu vaccine (0.0047%). Respective rates of serious AEs (eg, death, life-threatening illness, hospitalization, prolonged hospitalization, persistent or significant disability, congenital anomaly) are 4.4 and 2.9 per 1 million vaccine doses each. However, the percentage of serious AEs among all reports is slightly higher with seasonal flu vaccines (6.1% vs 5.4%). No substantial differences are noted between pandemic and seasonal flu vaccines in the types of serious AEs reported, and no AE differences between injectable and intranasal vaccines are apparent.

Among the 13 reported deaths of those who received the pandemic flu vaccine, 9 were associated with a "significant" underlying illness; 1 was the result of a motor vehicle accident; and 3 cases are under review by the CDC. There are 12 reports of Guillain-Barre syndrome (GBS), 4 of which currently meet diagnostic criteria, and 19 reports of possible anaphylaxis. (The background incidence of GBS is 1-2 per 100,000.)

In the VSD**—which includes data from more than 400,000 vaccinated individuals among 8 managed-care organizations—there are no reports of GBS and only 1 case of anaphylaxis. Increased rates of other neurologic or allergic conditions have not been detected.

Historically higher rates of GBS associated with the swine-flu vaccination in the mid-1970s may be related to contemporary methods of vaccine production, the CDC speculates. The Center reports that it continues to monitor vaccine-associated AE data and advises that the number of vaccines administered in the VSD population, in particular, may be too small as yet to detect an increased risk of vaccine-associated GBS.

As of December 3rd, more than 72 million doses of pandemic flu vaccine have been allocated in the United States.

N.B. The CDC states that it used a number of methods (eg, advertising in medical journals) to enhance the reporting of vaccine-associated AEs to VAERS this season.

* As of November 24, 2009.

** From October 1 to November 21, 2009.