Strep’s variations make vaccine elusive — so far

Dear Doctors: There are vaccines available for quite a few bacterial diseases and infections, but we still don’t have one to protect against strep throat. Is there a reason that the pharmaceutical companies have yet to develop such a vaccine, despite the obvious need for it?

Dear Reader: Although researchers and drug manufacturers have been working to crack the code of a global strep vaccine for several decades, success has proven elusive. That may be why their efforts have mostly flown under the radar. In recent years, as various research teams announced breakthroughs, there has been a sense the goal may be in sight. However, as you point out, a global strep vaccine has yet to become available. This is due in large part to the nature of strep bacteria.

Strep is short for streptococcus. Although there are several types, most illnesses are caused by group A or group B strep. When someone is diagnosed with strep throat, it’s a group A infection. The bacteria travels on the respiratory droplets an infected person releases when sneezing, coughing or speaking.

While strep throat is the best-known illness this bacteria causes, it’s not the only one. A range of other diseases, including the skin infections impetigo and cellulitis, are caused by strep A. In these cases, direct contact with an infected sore, or secretions from the sore, can also transmit the bacteria. Other serious illnesses driven by strep A include scarlet fever, rheumatic fever, rheumatic heart disease, necrotizing fasciitis and toxic shock syndrome.

Group B strep can cause blood infections, pneumonia and meningitis in newborns. Older adults, particularly those with existing health problems, are also vulnerable to strep B. This includes urinary tract or skin infections and pneumonia.

Worldwide, more than 750 million people fall ill from a group A strep infection each year. It causes at least 500,000 deaths per year, mostly in areas of low income. The only treatment is the use of antibiotics.

Elizabeth Ko, MD and Eve Glazier, MD

Among the challenges of developing a vaccine against strep is the bacteria’s diversity. There are more than 200 different known strains of strep A. Each has a slight but crucial structural difference, which the immune system must learn before it can mount a successful defense. In order to develop an effective vaccine, researchers must identify a characteristic in strep A that is universal to all strains. This has proven to be a steep hill to climb.

At the same time, strep A bacteria lacks an external membrane. This leaves it extremely vulnerable to the effects of antibiotics, including penicillin. In nations with robust health care systems, this vulnerability makes it fairly easy to treat a strep A infection with a course of antibiotics. It also lowers the interest in a vaccine. But in poorer nations, where people often have little or no access to medical resources, the annual burden of strep infections remains severe.

Now, with the growing threat of antibiotic resistance, a new urgency has entered the search for a strep vaccine. It makes the outcomes of the clinical trials currently in progress important to everyone.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)


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