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pharmafile | July 21, 2008 | News story | Sales and Marketing |Â Â Â
Immunisation against S. aureus has potential in selected target groups
Staphylococcus aureus bacteria have become a key concern in both the hospital and community setting. The spread of resistant strains, such as MRSA, underlines the urgent need for new strategies to treat and prevent these infections. Prophylactic vaccination of target groups could be a useful tool, but prudent group selection combined with alternative prevention strategies, will be key to success.
Staphylococcus aureus (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, affecting a wide range of different patient groups. Infections are associated with a longer hospital stay, a poorer clinical outcome and high treatment costs.
Many resistant strains of S. aureus have emerged, mainly due to antibiotic overuse. 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 these methods have achieved some success, their overall impact on infection rates has been limited. Furthermore, considering the rapid spread of S. aureus in the community setting, they are unlikely to remain efficacious in the long run. In addition, the emergence of resistant S. aureus strains further reduces treatment options.
Several new antibiotics that 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, but 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.
Therefore, development of a prophylactic S. aureus vaccine would present a huge commercial opportunity and several companies, including Nabi Biopharmaceuticals, Intercell/Merck, VRi 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, and immuno-compromised people, such as dialysis patients. Although all these patient groups would benefit largely from preventive vaccination against the pathogen, some, 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.
As a consequence of these challenges, immunisation is unlikely to become a one-size-fits-all approach. Instead, different patient groups are likely to benefit from different preventive strategies. Immuno-competent patients undergoing elective, high-risk hospital procedures, such as orthopedic or cardiovascular surgery, are likely to benefit greatly from prophylactic S. aureus vaccination. Moreover, a vaccine with a good efficacy profile in people aged 65 and over could have a large commercial opportunity in the elderly patient population, members of which are more likely to require frequent and lengthy hospital stays, and are therefore at a higher risk of S. aureus infections.
However, due to their weak immune system, other groups at a high risk of S. aureus infection 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.
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