Chlamydia has no vaccine yet. Why?

Chlamydia is a genus of bacteria. It has a lot of different types. Chlamydia trachomatis is a sexually transmitted human pathogen is the most common cause of preventable blindness in the world. There are more than 5330 publications about Chlamydia trachomatis, as we can see on the figure below majority of them – 2745 – were published in USA  followed by UK and Canada. The most cited publication on this topic is called “Genome sequences of Chlamydia trachomatis MoPn and Chlamydia pneumoniae AR39.” ( 232 citations), and it’s a good place to start your in-depth study.

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Most people recover from Chlamydia trachomatis infection without symptoms, but in the meantime, infect their sexual partners. Interestingly, this type of bacteria pathogen infects many other animal species. For example, it was recently identified as one of the major causes of declining numbers in world’s koala population. It’s not a surprise, that the majority of research on chlamydia incidence in koalas is done in Australia. There are only 49 publications about koalas and chlamydia so far. So if you are interested in this lovely eucalyptus-eater (…and chlamydia research), here is a place for you to start.

There are more than 2840 publications about another type of chlamydia, Chlamydia pneumoniaeThis bacteria causes pneumonia in humans. It is also quite valuable for the research in evolutionary biology of pathogens, because it’s primary host is human and apparently, has no animal or bird host. This disease was evolving with us, since our beginning as a spices. Sadly, we didn’t get rid of this unwanted fellow traveler yet. Currently, Chlamydia pneumoniae is responsible for approximately 10% of all pneumonia cases.

Chlamydia psittaci is the causative agent of psittacosis, a disease characterized by pneumonia, headache, altered mentation, and hepatosplenomegaly (simultaneous enlargement of both the liver and the spleen). Psittacosis is acquired from infected birds.  Luckily, psittacosis is a rare disease. Only 100 to 200 cases are reported annually in United States. It’s rare occurrence could be a partial explanation of the fact, that the global research for this type of chlamydia is nearly 13-times smaller than the research for Chlamydia trachomatis.

From above-mentioned, it’s obvious that potential invention of broad-spectrum vaccines against chlamydia could improve the quality of life for many humans (… and koalas!). Why don’t we have it yet and do scientists even try to develop it?  Oh yes, they do. The first attempts were made in late 1960s. However, these attempts backfired and as a result, the vaccine increased the vulnerability to the disease in treated patients. This case is often articulated as evidence for vaccination pitfalls by anti-wax groups. However, what they fail to mention is that the tests detected the unwanted reaction in early stages of development (as it should be) and thus, researches discontinued research. The burden of topic was holding researches back for several decades and the effect of this can be observed even today.

Due to an unsuccessful attempt in 1960s, miscommunicated by media, the further trials for chlamydia vaccines were dropped. But when we look at the figure below, we can see that tides are changing. In the last 15 years, there was rising trend in chlamydia vaccine research, although, the size of the research is much smaller compared to the research on measles a mumps vaccines. We need to push more.

 

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 The currently most cited article about chlamydia vaccine is “Immunology of Chlamydia infection: implications for a Chlamydia trachomatis vaccine.” with 111 citations. It is an exeptional and promising paper. The scientists with the highest number of published papers in this field are Luis M. de la Maza and Guangming Zhong. We believe that heroes like them and many others, who work in the research paradigm of the chlamydia vaccine will soon find a way to first lower the incidence of chlamydia disease and finally, eradicate this bacteria for good.