Apparently, the bug is a strain of strep bacteria not included in the pneumococcal vaccine, which became available in 2000 and is recommended for children under age 2. Prevnar prevents seven strains responsible for most cases of pneumonia, meningitis and deadly bloodstream infections. But dozens more strep strains exist, and some have flourished and become impervious to antibiotics since the vaccine combats the more common strains.
If the new strains continue to spread, "it tells us the vaccine is becoming less effective" and needs to be revised, Dennis Maki, infectious diseases chief at the University of Wisconsin-Madison Hospitals and Clinics, tells the AP.
Wyeth anticipated this development, the AP writes, and is testing a second-generation vaccine. But it is at least two years from reaching the market, and the new strains could become a public health problem in the meantime if they spread hard-to-treat infections through day care centers and schools. Might this crimp Prevnar sales, which nearly hit $2 billion last year?
"I don't think the new strains are moving fast enough to call it a race, but the fact is that certain strains are increasing," Peter Paradiso, a scientist at Wyeth Vaccines, the Collegeville, Pa., division that makes Prevnar, tells the AP.
"It is very worrying," says Keith Klugman, an infectious diseases specialist at Emory University. "With the eradication of all the other types in the vaccine, this one is emerging."
Several research teams reported on the situation Monday at a microbiologists meeting. A different pneumonia vaccine has long been available for adults but it doesn't work in children, so Prevnar was hailed as a breakthrough, which is used in dozens of countries. In the US, it is given as four shots between 2 months and 15 months.
Before the vaccine, many babies and toddlers developed pneumonia, meningitis and serious blood infections that led to hearing loss, brain damage and even death. Drug-resistant ear infections also were a problem. "Prevnar has done a remarkable job. Over the last seven years, it's prevented thousands and thousands of infections," not just in vaccinated kids but also in unvaccinated family members, says Cynthia Whitney, chief of respiratory diseases at the CDC.
But Prevnar is a unique vaccine because it covers only seven of the 90-odd strains of the germ. By contrast, measles is caused by one type of virus. Booster shots are needed for chickenpox, mumps and measles because immunity wanes, not because the germ changed.
Prevnar, however, is losing its punch because strains not covered by the vaccine are filling the biological niche that the vaccine strains used to occupy, and they are causing disease. One strain in particular, called 19A, is big trouble. A new subtype of it caused ear infections in the nine Rochester children, ages 6 months to 18 months, that were resistant to all pediatric medications, said Dr. Michael Pichichero, a microbiologist at the University of Rochester Medical Center.
The children had been unsuccessfully treated with two or more antibiotics, including high-dose amoxicillin and multiple shots of another drug. Many needed surgery to place ear tubes to drain the infection, and some recovered only after treatment with a newer, powerful antibiotic whose safety in children has not been established.
Pichichero refused further comment because he has submitted a report to a medical journal. His work was paid for by antibiotic maker Abbott Labs, a rival drugmaker, and the Thrasher Foundation, which funds projects related to child health.
All 19A strep subtypes tend to be resistant to some drugs and have been growing in prevalence:
- Scientists from a drugmaker and two labs analyzed more than 21,000 bacterial samples from around the nation and found 19A increasing. Among children 2 and under, the portion of samples that were this strain rose to 15 percent in 2005-2006, from 4 percent in the previous three years;
- A UK lab tracking respiratory infections in US kids found that the 19A strain accounted for 40 percent of drug-resistant cases;
- University of Iowa researchers found 19A accounted for 35 percent of penicillin-resistant infections in 2004-05, compared with less than 2 percent the year before the new vaccine came out.
Because these bacteria easily swap gene components to become even more hardy, "new types may emerge that can both escape containment by vaccine and spread throughout the world," Dan Musher of Baylor College of Medicine wrote in the New England Journal of Medicine last year.
Some think Prevnar might be destined to be like flu shots that must be periodically updated to reflect new strains causing illness. But each tweak requires new safety studies and more expense. Wyeth's Paradiso says testing on an updated vaccine should be finished next year and would be submitted to the FDA in early 2009, but a review can take a year or more.