PORTLAND, Ore. -- Kaiser Permanente says anyone who was possibly administered an ineffective flu vaccine in recent days may come in for another shot.

The hospital announced earlier this week that some patients who received flu vaccinations between Oct. 18 and Oct. 21 may have gotten ineffective shots because the vaccine had been exposed to cold temperatures.

Kaiser officials said it was impossible to determine who received ineffective doses during that time period and has recommended that everyone who got a shot between those days be revaccinated.

The hospital says there are no health risks from receiving an ineffective flu vaccine.

Kaiser was checking with the manufacturer to determine if the vaccines were ineffective and if anyone in Portland and Vancouver would be able to get a second dose.

CDC guidelines indicated revaccination would be safe if it was determined the shots were ineffective.

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The company said no more bad batches were going out.