(CBS) — The flu epidemic is being blamed for another problem in the Chicago area: a shortage of certain blood types.

Donations generally drop mid-winter, but this flu season hit far more people far earlier than usual. As a result, both Lifesource and the American Red Cross say they’re in need of RH-negative donors.

Both are calling for Type O-negative donors, while the Red Cross also seeks Type B-negative.

Lifesource spokesperson Tammy Basil said O-negative is the “universal donor,” a blood type that can be given to anyone in the event it is needed in an emergency.

But when is it OK to give?

Red Cross spokesman Ben Corey said being vaccinated for the flu is not a problem.

“There is no waiting period to give after receiving the vaccine, as long as you’re feeling healthy and well the day of the donation,” Corey said.  “Donors experiencing flu-like symptoms, such as fever, appetite loss, coughing or sore throat should not donate until 24 hours after the symptoms have subsided.”

Both agencies require blood donors to be at least 17 years of age, although those who are 16 can donate with parental consent. There is no upper age limit. Donors must weigh at least 110 pounds.

Overall, Corey says, the supply is adequate, but Basil said Lifesource is promoting a blood drive at Soldier Field between 9:30 a.m. and 3:30 p.m. Saturday, featuring members of the 1985 Chicago Bears.

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