As the result of a nationwide flu vaccine shortage, University Health Services (UHS) will only give shots this year to Harvard affiliates deemed to be at high risk for complications from the illness.

Those who will be given priority when flu shots become available Thursday include people over the age of 65, infants between the ages of 6 and 23 months, pregnant women and those with underlying chronic medical conditions such as diabetes, cancer or lung problems.

“We’ve all been asked to do this,” said UHS Director David S. Rosenthal ’59 on Friday. “All health providers and hospitals have been asked to focus on high risk individuals.”

Contamination at the Chiron Corporation plant in Liverpool, England, which manufactures about 50 percent of the United States’ flu vaccination supply, caused the shortage.

British health authorities suspended Chiron Corporation’s manufacturing license for three months.

Of the 14,000 doses UHS ordered, 8,000 were slated to come from Chiron. The other 6,000 have already arrived as scheduled from another supplier.

The city of Cambridge helped UHS secure another 2,400 units to help alleviate the shortage, Rosenthal said, in part because last year, UHS allowed city residents to use some of its excess vaccinations.

“We had been calling all over the place. Most of the lines were busy,” Rosenthal said.

But UHS expects demand to fall between 12,000 and 13,000 for the 8,400 shots available.

To verify whether someone is a high-risk individual, UHS officials may consult students’ medical records—“but in general people are very honest,” Rosenthal said.

UHS’s definition of high risk individuals is in line with those recommended by the Centers for Disease Control and Prevention.

Adams House Master Sean Palfrey, a professor of pediatrics and public ealth at Boston University, said yesterday that low-risk students should not panic if they are unable to get a flu shot.

“I don’t think it’s a problem for Harvard students in the sense that they’re at an age where we should know that they’re at an increased risk,” Palfrey said. “It’s more of a problem for infants and elder citizens who are at risk and may not actually get the vaccine.”

Because of the shortage, Rosenthal warned that people should maintain a high level of cleanliness and hygiene this season.

“We are promoting alcohol-based gels,” Rosenthal said.