United Press International - October 11, 2005

The report, "Vaccine development: Current Status and Future Needs," which was prepared by the American Academy of Microbiology, also foresees new vaccines as fighting off the new epidemics of the 21st century.

"The success of vaccines in controlling disease has been profound," said Dr. James Kaper of the University of Maryland School of Medicine. "Many diseases that formerly raged unchecked are now under control and others have been eliminated in parts of the world. Despite this success, infectious diseases continue to be public-health problems particularly in developing countries where vaccines are unavailable, unaffordable, or both."

The report identifies more than 40 infectious agents that pose significant human health problems in the United States and abroad, the most significant of which is HIV.

"Vaccines are available for some diseases that continue to plague humans, but not for others," said Dr. Rino Rappuoli, of Chiron SpA in Siena, Italy, the report's co-author. "Even when a licensed vaccine is available for a given disease, numerous barriers can block its use, including technical, economic, cultural, and legal obstacles."

Of the infectious agents identified, only 12 currently are being combated by effective vaccines. Others are relatively rare today, but could be poised to re-emerge, by either natural means or terrorism, such as avian influenza, West Nile virus and botulism toxin.

The report assesses the prospects of selected new-vaccine developments as follows:

--Human immunodeficiency virus: An effective and safe vaccine remains "elusive." At present, more than 70 prospective HIV vaccines have undergone Phase I trials, and several have gone to Phase II trials, but only two experimental vaccines made it to Phase III.

"Given the limits of the available technology and the current state of knowledge on HIV, in the short-term it appears unrealistic to expect an HIV vaccine to achieve ... eradication of the virus from the immunized system," although "even a less-than-ideal vaccine could have a substantial impact on the spread of the HIV pandemic."

--Human papilloma virus: Two promising vaccines are undergoing advanced clinical trials, but questions about when to vaccinate and whether vaccination should be tailored differently for men and women have emerged. Also, an HPV vaccine probably will be "prohibitively expensive for use in the developing world, where it is needed most," the report said.

--Herpes simplex virus: A variety of experimental vaccines for HSV are in development. Development has been slowed by a lack of understanding about natural immunity to the virus and unknowns about the size of the prospective market.

--Chlamydia trachomatis: A few candidate vaccines are in the early stages of development, but the chronic nature of the disease, lack of understanding about protective immunity to the infection, problems with funding, and questions about the target market for a prospective vaccine continue to hamper development efforts.

--Neisseria gonorrhoeae: Many different types of vaccines may be feasible. Early studies on candidate vaccines have shown that these formulations can be effective in preventing infection, but a lack of appropriate in vitro systems and animal models has slowed progress.

--Treponema pallidum: No vaccines for the bacterium responsible for syphilis are currently available.

--Escherichia coli: Although urinary tract infections are extremely common, a vaccine for the E. coli strains commonly responsible for this condition has yet to be developed. Identifying a conserved common antigen shared by all of the potential offending E. coli strains is a daunting prospect that few vaccine developers are willing to tackle, especially given the minor role these infections play in overall public health.

--Influenza virus: Despite the annual development and distribution of attenuated and inactivated influenza vaccines tailored to the anticipated dominant strains of the season, influenza climbs to epidemic proportions in the U.S. and elsewhere every year. Production of the vaccine and the vaccine itself are fraught with problems, and improvements are desperately needed. Pinpointing the flu strain that will be dominant in a given year often poses difficulties, as strain variation cannot always be anticipated. Development of an influenza vaccine that can reduce community spread or cover the drifted strains that appear in the midst of flu season would have a considerable impact.

--Respiratory syncytial virus: Although urgently needed, a vaccine for RSV is not currently available. A live attenuated vaccine is undergoing clinical trials, but this formulation may carry excessive risks for infants.

--Parainfluenza virus: A licensed vaccine is not available, but an experimental formulation is in the early stages of human trials. The need to develop a multivalent vaccine effective against the various serotypes has posed an impediment to progress and constitutes a daunting prospect for prospective manufacturers.

--Mycobacterium tuberculosis: Despite efforts by vaccine developers over the years, only one vaccine for tuberculosis is available on the market today: the bacillus calmette-guerin vaccine, which has proven effective, but does not induce long-term immunity.

--Haemophilus influenzae type B: "Superb conjugate vaccines" currently are in use, including formulations that are combined with whole-cell pertussis, diphtheria and hepatitis B vaccines, formulations that are useful in delivering the necessary vaccines to residents of developing nations.

--Streptococcus pneumoniae: Effective vaccines for pneumococcal diseases are in great demand for both industrialized and developing nations. S. pneumoniae is the most common bacterial cause of hospitalization for pneumonia, meningitis, and acute otitis media in the very young and the elderly in industrialized countries. In developing countries, this pathogen is a major cause of morbidity and mortality among infants and young children, largely due to pneumonia.

--Group A Streptococcus pyogenes: Several interesting candidate vaccines are undergoing clinical trials, but it has taken vaccine developers many years to get this far. Problems in developing Group A strep vaccines have ranged from providing adequate protection from each of the various Group A serotypes to preventing the inadvertent induction of rheumatic fever and rheumatic heart disease.

--Chlamydia pneumoniae: Several candidate vaccines are in the early stages of development and have yet to be tested in clinical trials. A lack of data on the role of protective immunity and insufficient understanding of the public health importance of C. pneumoniae stand in the way of faster progress in developing a good vaccine.

The complete report is available online at: asm.org/ASM/files/ccLibraryFiles/Filename/000000001841/VaccineDev-TextOnly.pdf

E-mail: sciencemail@upi.com
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