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Evolution of whooping cough and the anti-vaccination movement

whooping cough

When I was your age, whooping cough wasn’t what it is today. I’m sure we all know the stereotypical grandfather telling stories like that, but — at least in this case — if he started his story off like that then he is actually right. Over the last few years, this once-common childhood illness, has evolved in response to its own vaccine, in other words this isn’t your parents’ pertussis.

As scary as this may sound, it could have “serious consequences” in future outbreaks. However, the experts stressed the vaccine remains highly effective in protecting the most vulnerable — young babies. The mutated virus is not more dangerous than the original, so the findings don’t change researchers’ and doctors’ understanding of whooping cough as a public health problem.

Instead, they’re a glimpse into a fascinating natural phenomenon, and one that’s happening as we speak. This is a very good and easy to see example of selective pressure, by not quickly eliminating the virus we are allowing it the chance to evolve around the vaccine. This a similar problem we have with the flu vaccine, which is why you can get one every year.  In fact, the whooping cough findings have kicked off research to determine whether this is related to the recent increase in whooping cough cases in the U.S.

“We discussed the data and what the data allow us to say and what they don’t allow us to say,” says Paul Offit, chief of the division of infectious diseases at the Children’s Hospital of Philadelphia.

“The data doesn’t support the notion that the mutants are more virulent.”

In other words, babies who fall ill from un-mutated pertussis have the same symptoms as babies who fall ill from mutated pertussis, says Offit, who was not involved in the CDC study, but took part in a conference call about the study in which CDC researchers presented their results.

There has been a global resurgence of whooping cough in recent years. In 2012, there were almost 10,000 confirmed cases in England and Wales – a dramatic increase from the last “peak” of 900 cases in 2008. The outbreak led to 14 deaths in babies under three months of age – the group who are most vulnerable to infection. These rising figures prompted health officials to recommend vaccination of pregnant women so immunity could be passed to their newborns – a strategy that a recent study showed was working well.

There’s currently no evidence yet that pertussis vaccines are less effective against the new strains, say researchers, both in and outside of the CDC. Everyone recommended Americans continue to get vaccinated right on schedule.

“Currently, we know it’s the best form of protection we have,” says Lucia Pawloski, the CDC scientist who led the new research.

It should be noted that kids who don’t get vaccinated against pertussis are still eight times as likely as vaccinated kids to get the disease. The researchers are still trying to work out what the changes mean in reality – for example do the mutations boost the ability of the bacteria to cause infection.

“We wanted to look at strains from the UK to see if there was anything sudden that had occurred that had led to these really large outbreaks,” said study leader Dr Andrew Preston from the University of Bath.

The “million dollar question” he said was what, if anything, could be done to improve the vaccine – which is still the best defence we have – and prevent future outbreaks. Options to consider include adding more or different proteins to the vaccine, adding novel adjuvants – chemicals which boost the immune response, or even revisiting the old-style whole cell vaccine, he said.

“Pertussis has a cyclical nature and other big question is are we going to see another increase in late 2015,” he added

“But the control of pertussis is a significant worry,” Prof Adam Finn, a paediatric immunology expert at the University of Bristol said.

Only 60% of pregnant women have had the pertussis vaccine and we should be doing more to raise awareness of its benefits, he said.

“There is very good new evidence that vaccinating pregnant women protects their babies. And the group we really want to protect is newborn babies,” he said.

I should probably mention that while the old-style whole cell vaccines have been shown to be more effective and longer lasting than the vaccine we use now (based from proteins found on the cell) it is still used in developing countries. The whole cell vaccine, which is cheaper to make, were discontinued in developed countries because they cause severe, if non-permanent, side effects, such as seizures(seen  in a fraction of a percent of babies). So determining the cause for the side effects would be important before the whole cell vaccine would be able to make a return to the US.

The bottom line is that the anti-vaccination movement is causing a serious problem, even if the argument that, “It’s my child” only goes so far since it only takes a few well placed mutations for something to go from, a at best nuisance and at worse deadly virus for some, to a deadly outbreak for millions vaccinated or not.

The problem is that for every one person a virus can infect, there is just one more chance for the virus to mutate (or evolve) into something that can circumvent the vaccine or even possibly become more deadly, that is how selective pressure works we are forcing it to change if it wants to survive. This is why we push so hard for vaccinations, we have and can eliminate a lot of these illnesses by successfully vaccinating the masses. Unfortunately it is now the “cool thing” to not get vaccinations and that is, at the very least, one of the causes of this problem with whooping cough. This is the same thing that is happening with the ebola and polio viruses and it needs to stop before it’s too late.

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Sources
Pawloski, L., Queenan, A., Cassiday, P., Lynch, A., Harrison, M., Shang, W., Williams, M., Bowden, K., Burgos-Rivera, B., Qin, X., Messonnier, N., & Tondella, M. (2013). Prevalence and Molecular Characterization of Pertactin-Deficient Bordetella pertussis in the United States Clinical and Vaccine Immunology, 21 (2), 119-125 DOI: 10.1128/CVI.00717-13

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