A new study supports the notion that giving Wyeth's (WYE) childhood vaccine Prevnar in fewer doses than some standard regimens is sufficient to protect against a bug that causes meningitis and pneumonia.

The finding could hurt sales of the best-selling vaccine in the world if more national governments opt for fewer doses in their immunization programs. But officials from Wyeth and the U.S. Centers for Disease Control signaled that was unlikely to happen in the U.S. anytime soon.

Prevnar has been credited with substantially reducing rates of so-called pneumococcal infections since its launch in 2000. Wyeth of Madison, N.J., sold more than 47 million doses of Prevnar worldwide in 2008, generating $2.7 billion in sales, 11% higher than the year before. It costs about $83 per dose in the private market in the U.S. The vaccine stands to be one of the prizes New York-based Pfizer Inc. (PFE) inherits when it closes its planned acquisition of Wyeth, expected later this year.

The 1,000-child study, financed by the Dutch Ministry of Health and conducted in the Netherlands, concluded that giving Prevnar to infants in two initial doses, followed by a booster shot, reduced the rates of carriage of the targeted bacteria in vaccinated children in the second year of life by about 60%, versus unvaccinated children.

Currently, Prevnar is given in three initial doses followed by a booster shot - known as 3-plus-1 - in the U.S., Germany, the Netherlands and elsewhere. However, other countries including the U.K., Sweden and Norway, already offer the vaccine as two initial doses plus a booster shot, or 2-plus-1, in their national immunization programs. The reduced-dose regimen matches the schedule for other childhood shots in those countries and has the added bonus of saving money.

"In my opinion you could safely go to two-plus-one," said Elisabeth Sanders, one of the study's co-authors and professor of pediatric immunology and infectious diseases at University Medical Center Utrecht in the Netherlands. "Why not save the one injection if it's not required?"

The study's results were published online Tuesday by the medical journal JAMA.

Although the new study didn't directly compare the 2-plus-1 regimen with 3-plus-1, Sanders said the reduced rate of bacteria carriage was comparable to that seen in other studies of the 3-plus-1 regimen.

Sanders said the reduced-dose regimen might be useful in developing countries, where resource constraints and logistics problems make it difficult to implement a 3-plus-1 schedule.

Emilio Emini, Wyeth's executive vice president of vaccine research and development, said the 2-plus-1 schedule can be effective, but he didn't expect any significant changes in dosing schedules in national immunization programs.

The U.S. schedule of "3-plus-1" has the benefit of rapidly building up immunity in infants, Emini said. He said he expects the Prevnar schedule to stay the same in the U.S. because it matches the schedules for other childhood vaccines.

The success of Prevnar in battling disease has stemmed not only from the direct protection provided to individuals but also in building up "herd immunity," in which unvaccinated or partially vaccinated people get protection because the targeted bugs don't circulate as widely as before the vaccine was introduced. Emini said the 2-plus-1 schedule relies more heavily on herd immunity to provide protection.

The U.S. CDC currently recommends infants receive Prevnar shots at two, four and six months, plus a booster shot between 12 and 15 months. Earlier this decade, the CDC temporarily recommended fewer doses due to supply shortages at Wyeth.

Matthew Moore, a medical epidemiologist with the CDC, said "we've had terrific success in this country with the existing schedule we have." The CDC estimates Prevnar has helped prevent more than 200,000 cases of pneumococcal disease since its launch.

The Dutch study also found that giving Prevnar in two doses only - with no booster shot - reduced carriage rates of the targeted bugs at two years by an amount similar to the 2-plus-1 schedule. But Sanders didn't recommend that countries adopt a two-dose-only regimen because it probably wouldn't offer long-term protection. Emini said such an approach would erode herd immunity over time.

Wyeth has developed a new vaccine designed to provide broader protection against pneumococcal disease, Prevnar-13, and is awaiting U.S. and European regulatory action. GlaxoSmithKline PLC (GSK) recently gained approval to sell a rival vaccine, Synflorix, in Europe.

-Peter Loftus; Dow Jones Newswires; 215-656-8289; peter.loftus@dowjones.com