Four years ago, when meningitis B, an extremely rare but potentially lethal form of the infection, sickened a small number of college students at Princeton and the University of California, Santa Barbara, there was no vaccine against the disease sold in the U.S. Despite its availability abroad, it had never been licensed in the country due to its limited marketability.

Scientific evidence supporting an absolute need to immunize against meningitis B still falls short. The risk of contracting it is smaller than that of being involved in a car crash.

But the headlines prompted by those 13 campus cases — which resulted in one death and one double amputation — helped reshape the financial prospects for a vaccine.

Today, two brand-name vaccines, both with price tags of more than $300, are widely advertised on television and touted as a smart investment for parents who love their college-bound kids.

"As moms, we send our kids out into the world, full of hope," says a mother in the ad for Bexsero, sold by pharmaceutical giant GlaxoSmithKline, as her son loads up the car to go off to college.

Says another voice, "And we don't want something like meningitis B getting in their way."

Analysts expect the two vaccines to generate hundreds of millions of dollars in global sales annually.

But with a new crop of students off to college, some physicians and other industry experts are uneasy about the role of marketing in leveraging parental fears to sell the MenB vaccine — as well as ever more expensive vaccines that prevent quite rare illnesses. A complete Bexsero series costs $320; a competing vaccine, Trumenba, costs $345.

"Parents believe their children are susceptible to this terrible condition, and [drugmakers] use that fear to get parents to take action," said Adrienne Faerber, a lecturer at the Dartmouth Institute for Health Policy and Clinical Practice who researches drug marketing.

The advertising, especially when coupled with news coverage, puts parents in a quandary left unresolved by federal vaccination guidelines and university requirements.

The Centers for Disease Control and Prevention recommends doctors consider the meningitis B vaccine for people ages 16-23 on an individual basis. This recommendation — ranked as a category B — is not as universal as the approach applied to illnesses such as measles or human papillomavirus vaccines or even the "quadrivalent" vaccine for meningitis A, C, W and Y, which all students must get.

Researchers don't know how long the meningitis B vaccine's immunity lasts. Many noted it also doesn't cover all strains of the infection, so its efficacy in the United States is uncertain (there are different strains in different parts of the world).

Meanwhile, insurers generally cover it as part of preventive care. Still, most universities don't require the vaccine but simply list it as an option for families to consider.

The resulting messages can confuse parents.

"There is perhaps, with all the marketing and advertising, some bending of the truth, and perhaps a little bit of creating fear — again recognizing that meningitis disease is a very severe disease," said William Moss, a professor at Johns Hopkins Bloomberg School of Public Health who specializes in vaccines and global children's health. "[The risk] is not a large enough problem to warrant routine vaccination."

In recent years, drugmakers' interests have begun to expand beyond the relatively cheap, broadly used immunizations — such as a tetanus shot or the children's hepatitis A vaccine — to new, much pricier ones for less common infections.

Already, industry analysts forecast Bexsero could bring in global revenue north of $1 billion per year by 2022. Trumenba is expected to earn Pfizer $880 million by that time.