Over the last decade Staphylococcus aureus (S. aureus) bacteria have become a key concern in both the hospital and community setting. The increasing spread of resistant strains such as MRSA underlines the urgent need for new strategies for treatment and prevention of these infections. Prophylactic vaccination of key target groups could provide a very useful tool for infection prevention, but prudent target group selection combined with alternative prevention strategies such as hospital hygiene improvement will be key to success in this challenging field, according to a new report* by independent market analyst Datamonitor.
S. aureus is the most frequent pathogen present in the hospital setting in most western countries. In the US alone, an estimated 292,000 hospitalisations with a diagnosis of S. aureus occur each year. The pathogen is by far the most frequent cause of skin and soft tissue infections and affects a wide range of different patient groups. Infections are associated with a longer hospital stay, a poorer clinical outcome and high treatment costs. Mainly due to antibiotic overuse, many resistant strains of S. aureus have emerged.
The most concerning of these is methicillin-resistant S. aureus (MRSA), which shows resistance to most available antibiotics and is therefore extremely hard to treat. The majority of severe MRSA infections in the US occur in the hospital setting, where they account for almost 20,000 deaths each year, with figures increasing rapidly over the last decade in both the hospital and - more recently - the community setting.
With S. aureus emerging as an increasing problem, considerable efforts are being made to reduce infection rates. Hygiene-improvement strategies, such as hand-hygiene programs, thorough disinfection of medical devices and isolation of infected patients have been implemented in many countries. However, although some success has been achieved with these strategies, their overall impact on infection rates has been limited thus far, and they are unlikely to remain efficacious in the long run, particularly considering the rapid spread of S. aureus in the community setting. In addition, the increasing emergence of resistant S. aureus strains further reduces treatment options, Datamonitor vaccines senior analyst Hedwig Kresse says.
“Several new antibiotics, which show good efficacy against S. aureus and even MRSA have been launched in the last two years. This means that good treatment options are available for the short- to mid-term future.
“However, it is only a question of time until S. aureus strains with resistance against the new drugs will emerge, particularly since most of these compounds are either molecules from long-established drug classes or closely related to older drugs.
“Antibiotic treatment is essentially a selection race between drug developers and pathogens, whereas preventive strategies such as vaccines have the potential to overcome this cycle,” she says.
As a result, a prophylactic S. aureus vaccine could have a large commercial opportunity and several companies, including Nabi Biopharmaceuticals, Intercell/Merck & Co, VRi plc and Inhibitex/ Wyeth are developing candidates that are currently in clinical trials.
However, vaccine design against S. aureus is associated with significant challenges. Populations at particularly high risk of S. aureus infection include the elderly, patients undergoing lengthy and complex surgery, people in long-term care as well as immuno-compromised people such as dialysis patients. Although all these patient groups would benefit largely from preventive vaccination against the pathogen, some of them (such as patients undergoing cancer chemotherapy, dialysis, or suffering from other acquired immune deficiencies) may not respond sufficiently to vaccination due to their weakened immune status, Kresse explains.
“Unlike conventional vaccines, which are mostly targeted at healthy children and adolescents with a fully functional immune system, S. aureus vaccines would most benefit many patient groups who have a weakened immune system due to their age or medical history. As a result, vaccination may prove inefficient in some of the aforementioned populations, as it is doubtful whether they can achieve protective antibody titers following vaccination.”
As a consequence of the challenges linked to vaccine design for some of the population groups at high risk of acquiring a S. aureus infection, immunisation is unlikely to become a one-size-fits-all approach for all patients. Instead, different patient groups are likely to benefit from different preventive strategies, Kresse says. “Prophylactic S. aureus vaccination is likely to add huge benefits for immuno-competent patients undergoing elective, high-risk hospital procedures such as orthopaedic or cardiovascular surgery. A vaccine with a good efficacy profile in people aged 65 and over could have a large commercial opportunity in the elderly patient population, which is more likely to require frequent and lengthy hospital stays, and therefore at a higher risk of S. aureus infections.
“However, due to their weak immune system, other S. aureus high-risk groups such as those undergoing cancer chemotherapy or requiring dialysis may benefit more from alternative methods of prevention such as antibody-based strategies. Overall, Datamonitor sees the greatest chances of success with regards to S. aureus infection control in a prudent combination of vaccination, antibody-based prevention and transmission control measures as part of hospital hygiene strategies,” she says.
Datamonitor's report Pipeline Insight: Nosocomial Vaccines - Minefield or Goldmine? provides a discussion of the market environment for nosocomial vaccines including epidemiology, costs and reimbursement structures and alternative prevention methods. Assessment of the pipeline and sizing estimates of patient potential for vaccines by pathogen.
