Thursday, June 30, 2005

Vaccines for ear infections

Middle ear infections are the most common childhood bacterial infections. In addition to the misery ear infections cause children and the sleepless nights they cause parents, the CDC estimates that the treatment of middle ear infections and their complications costs the U.S. approximately $4-$5 billion each year. Worldwide, these ear infections are a major cause of hearing impairment that can have serious negative long-term effects on children's language, speech and mental development.

The fluid and mucus buildup inside the ear that is the hallmark of acute middle ear infections creates pressure that can pain, loss of equilibrium, and eardrum rupture. Children can also suffer from high fever. Myringotomies (installing tubes in the ears) and adenoidectomies (adenoid removal surgery) done in response to chronic middle ear infections rank as some of the most common surgeries performed on children.

Although antibiotics have proven to be an excellent treatment for ear infections, parents and caregivers may forget doses or misunderstand instructions. Children may find the medicines bad-tasting and resist taking them. Some parents, upon seeing that their child is feeling better, may mistakenly stop giving the medicine. This, along with other common misuses of antibiotics, is leading to the development of antibiotic-resistant strains of bacteria.

To more effectively combat this childhood scourge, researchers around the world are working on developing vaccines against a variety of pathogenic bacteria that have been implicated in ear infections.

One vaccine, Prevnar, protects children from Streptococcus pneumoniae bacteria, one of the most common culprits behind ear infections as well as more serious diseases like meningitis. Prevnar was approved by the U.S. Food and Drug Administration in early 2000. To work most effectively, it must be injected into babies when they're 2, 4 and 6 months old; they will also need a booster when they're a little over a year old. However, after all those shots, Prevnar does not work against all the bacterial species that can cause ear infections.

A recently-developed vaccine against influenza has had the fortunate side effect of noticeably reducing children's rates of getting ear infections. This vaccine, which nominally works against the influenza virus, helps protect against secondary bacterial infections because the bacteria often get their first foothold during the swelling, inflammation, and congestion caused by colds and the flu. The vaccine is given as a nasal spray, but has not been approved for widespread use yet. The vaccine is being studied by several laboratories with researchers at Saint Louis University taking the lead.

Researchers at Children's Hospital in Columbus, OH are studying pathogens such as nontypeable Haemophilus influenzae (NTHI). According researchers there, the vaccine they develop must work effectively and safely in young infants, because children who get infections before their first birthday tend to get a colony of bacteria established that keep coming back and causing problems. Developing such a vaccine is a a challenge, because children under the age of two don't stage the same kind of immune response to vaccines as older children.

Some of the researchers there are working on sequencing H. influenzae genome to more fully understand its pathogenesis. Others are working on understanding the biomolecular mechanisms through which the bacteria cause disease. So far, they have identified and extensively studied a NTHI bacterial adhesin which looks like a good candidate for a vaccine. The adhesin, P5-fimbrin, has been worked into two different experimental vaccines that are being tested in rodents. Other labs in Australia and Belgium are working with the vaccines as well.