With a more virulent-than-usual influenza season well under way, MedImmune says it’s ready to meet vaccine demands, even as it prepares to release a more protective, four-strain vaccine next season.

The Gaithersburg producer of the FluMist nasal spray vaccine produced 12 million doses for this flu season, with an additional 310,000 extra doses with February expiration dates that can be shipped at a moment’s notice, Melissa Garcia, manager of product public relations, wrote in an email to The Gazette. An additional 70,000 extra doses carry an expiration date of March and also could be shipped quickly.

Such measures might be needed, as 42 states are reporting widespread flu activity, according to the federal Centers for Disease Control and Prevention in Atlanta.

About 143 people were hospitalized in Maryland through the week ending Dec. 31 for flu-related symptoms, with 2,317 people arriving at emergency rooms, according to the state Department of Health and Mental Hygiene. The state also has reported six outbreaks. A year ago, flu-associated hospitalizations totaled only about 57.

State officials have called this the worst flu season since 2009, which involved 500 hospitalizations between Sept. 28, 2008, and May 23, 2009. Some of that outbreak involved the H1N1 swine flu.

“While we can’t say for certain how severe this season will be, we can say that a lot of people are getting sick with influenza and we are getting reports of severe illness and hospitalizations,” Joe Bresee, chief of the epidemiology and prevention branch of the CDC, said in a statement last week. The agency is urging vaccinations, causing some reported shortages around the nation.

MedImmune also has a reserve order for 250,000 doses that would be shared between Medicaid’s Vaccine for Children’s program and the Department of Defense, contributing to their reserves for a total of 620,000 extra doses.

“Given this surplus for available doses, we would not consider producing additional FluMist for this season until all current inventory was used and additional, significant demand existed,” Garcia wrote.

MedImmune — the biologics division of British pharma giant AstraZeneca — typically takes customer prebook orders for the vaccine from January through March to prepare for the upcoming season, with most shipping in July and August, she said. Production takes about six months, with the Food and Drug Administration’s Vaccine and Related Biological Products Advisory Committee determining which flu strains manufacturers should include.

FluMist is approved only for people ages 2 to 49.

FluMist sales in 2011 totaled $161 million, almost entirely in the U.S., according to AstraZeneca’s latest annual report with the Securities and Exchange Commission. That was down 7 percent from 2010.

In late February, the FDA approved MedImmune’s application to market the first quadrivalent flu vaccine, which targets both A and both B strains. MedImmune is taking orders for this vaccine for the upcoming 2013-14 season and will begin production after the FDA advisory committee meets in February, Garcia said.

Garcia said that six of the 11 flu seasons in the U.S. from 2001 to 2012 involved a predominant circulation of influenza B lineage that was different from the one selected for inclusion in the conventional trivalent vaccines that are designed to confer immunity against three strains.

“Illness caused by Influenza B virus affects children, particularly young and school-aged, more than any other population,” Karen Midthun, director of the FDA’s Center for Biologics Evaluation and Research, said in a statement when the four-strain vaccine was announced.

“A vaccine containing the four virus strains most likely to spread and cause illness during the influenza season offers an additional option to aid in influenza prevention efforts,” Midthun wrote.

Novavax in Rockville also has been working on a quadrivalent seasonal flu vaccine using its virus-like particle technology. The company launched a Phase 2 clinical trial of the candidate this year in Australia.

While conventional vaccines use either killed or weakened virus strains to spur the body to generate antibodies, Novavax’s technology is designed to confer immunity by using the genetic code of the virus, rather than the actual virus. The vaccine can thus be produced more quickly, can be more effective and can result in fewer adverse effects than conventional vaccines, according to company information.

lrobbins@gazette.net