San Francisco ? Vaccines can be financially risky to discover and market compared with the opportunity to cash in on blockbuster drugs, but some companies still find them an exciting and lucrative business.

Economic disincentives ranging from difficult manufacturing and licensing procedures to unattractive accounting rules have contributed to vaccine shortages in the past few years, and may lead more companies to get out of the business unless the government provides more incentives, according to studies published in the May/June edition of Health Affairs.

But some pharmaceutical and biotech companies say they are committed to making vaccines to prevent a number of debilitating and potentially fatal ailments, including HIV and the agents that cause cervical cancer, hepatitis C, shingles and West Nile virus.

Merck, for example, has been making vaccines for more than 100 years and has no plans to stop, said Kelley Dougherty, director of public affairs for Merck’s vaccine division.

“We have a high level of dedication to staying in the business of vaccines,” she said, adding, “We definitely acknowledge it’s a challenging business.”

And despite last year’s suspension of flu-shot production, Chiron remains dedicated to that market and others within its vaccine businesses, spokeswoman Alison Marquiss said.

Delicate process

Vaccine investigation isn’t just happening among big pharmaceutical companies. In May, U.S. vaccine maker Acambis reported promising early results from the first round of trials for its West Nile virus vaccine.

Acambis received a $3 million grant from the National Institutes of Health in 2000 to develop a vaccine for West Nile, which is transmitted by mosquitoes.

More than 16,600 people have been infected since the virus was first spotted in New York City in 1999. About one in five infected people develop West Nile fever, which can make them sick for a few days or weeks. Less than 1 percent develop neuro-invasive disease, which can be fatal.

Frances Welch, 95, rolls up her sleeve in preparation for a flu shot from registered nurse Randy Kortness at a flu shot clinic hosted by a grocery store in Seattle, in this Dec. 7 file photo. Some pharmaceutical and biotech companies say they are committed to making vaccines to prevent a number of debilitating and potentially fatal ailments.

The influenza vaccine is a particularly difficult one to make because its components change year to year and the process of growing it in chicken eggs is lengthy and delicate, leaving little margin for error. And, unlike routine childhood vaccinations, demand for the product is highly variable.

Chiron has already cited delays in startup procedures in lowering its forecast of available doses of its Fluvirin flu shot this fall to between 18 million and 26 million, down from 25 million to 30 million.

Despite the most recent setback and last year’s blow, Chiron has no plans to abandon its flu-vaccine business and expects healthy demand, Marquiss said.

Sanofi Pasteur is operating its flu-vaccine manufacturing in Swiftwater, Pa., at maximum capacity and is aiming for around 50 million doses this year, spokesman Len Lavenda said.

Increasing demand

Despite intermittent supply problems, infectious-disease experts are considering recommending universal vaccination, meaning every American should get immunized against flu each year. The CDC already recommends vaccination for more than 180 million Americans, though millions of excess doses often go to waste.

Decreasing the number of underinsured people also may contribute to boosting the vaccine market, according to a study in Health Affairs.

An estimated 30 percent of privately insured U.S. adults and 15 percent of children lack coverage for new vaccines, the study found.

But about 78 percent of Americans say they’d pay $3 to $6 more a month to have their health plans automatically cover newly recommended vaccines for adults and children.

Those in favor tend to believe vaccines are both safe and effective, said Dr. Matthew Davis, co-author of the report and an assistant professor at the University of Michigan.

“The study suggests there’s a strong public demand for new vaccines on the short-term horizon,” Davis said. “That may be a reassuring sign for vaccine manufacturers that there’s a market for their products.”