Potency drops investigated in H1N1 vaccines

As reported earlier, the low potency of some H1N1 vaccines has led to product recalls and in one case the re-inoculation of individuals who received a weakened shot. Sanofi-Aventis and AstraZeneca's MedImmune have low-potency recalls underway, and some 2,000 Ohioans who visited an H1N1 clinic were called back for a second jab because their first had been frozen in shipment.

The mid-December Sanofi recall involves 800,000 doses of thimerosal-free vaccine in pre-filled syringes for children under age three. Just a week later, MedImmune issued a low-potency recall of 4.7 million doses of intranasal child vaccine. Neither poses a safety risk.

An AstraZeneca spokesman says in a Reuters report that the vaccine doses were within potency spec at the time of distribution and that the cause of the potency loss is being investigated. At Sanofi, testing showed adequate potency when the vaccine was made, but low potency after storage, reports the LA Times. A root cause analysis is in process.

The U.S. Centers for Disease Control and Prevention notes the importance of proper cold chain storage and shipment to vaccine potency. It estimates that 17 to 37 percent of providers expose vaccines to improper storage temperatures.

But maybe a less potent vaccine will turn out to be just what the doctor should order: a study reported in the New England Journal of Medicine finds that H1N1 is less contagious than previous pandemic viruses.

- see the Reuters report
- here's the LA Times article
- read the CDC cold chain information sheet
- see the contagion study