by Natalie Ring
You may have heard the news that measles has been making a comeback over the last few years. In 2015, there was an outbreak in Disneyland, which affected several hundred people across the USA, Mexico and Canada, who had recently visited Disneyland in California. These measles outbreaks have been mainly caused by a massive decrease in the number of people getting vaccinated against the disease.
Measles, along with Mumps and Rubella, is one of the diseases targeted by the MMR vaccine. In the 1990s, a single study claimed that there was a link between the MMR vaccine and autism, this has since been disproved but there are still many people (anti-vaxxers) who no longer want the MMR vaccine. Once the numbers of people getting the vaccine for any disease fall beneath a certain threshold (known as the “target coverage”), we’ll start to see the disease reappearing – and that’s exactly what’s happening with the measles now.
One lesser known disease that has also been making a comeback is whooping cough, which is also sometimes called Pertussis after the bacteria which cause it, Bordetella pertussis (B. pertussis). For most people, whooping cough is just an annoying cough that refuses to go away. It starts with symptoms similar to a cold, then progresses to a very persistent cough - people with whooping cough sometimes cough so much that it makes them sick. If diagnosed early enough, whooping cough can be treated with antibiotics.
Unfortunately, because the early illness looks so much like a bad cold, many people don’t get diagnosed early and, once the illness has progressed to the coughing stage, it’s probably too late for antibiotics to help. That’s because the cough itself is a side-effect of a toxin produced by B. pertussis. Pertussis toxin causes damage to your airways, resulting in the characteristic cough which ends with a whooping noise. By the time that damage is done, your immune system will probably have killed the bacteria in your body by itself, and antibiotics won’t be able to fix the damage, so you just have to wait for your airways to heal by themselves. This healing generally takes about three months, meaning you could be coughing and whooping for months on end!
So why haven’t most of us heard much about this annoying disease, which at one point was as common in childhood as chicken pox still is? It’s mainly because a vaccination for whooping cough was introduced around the world in the 1950s, and the vaccination resulted in a huge decrease in the number of people getting infected. Thanks to the vaccine, for a long time, whooping cough was no longer a disease that everyone could expect to catch at some point or another.
The story of the whooping cough vaccine
At first, the whooping cough vaccine contained whole dead B. pertussis cells. Introducing the body to these cells allowed the immune system to teach itself how to fight against whooping cough. Unfortunately, this vaccine had some undesirable side effects, like swelling and fever, which led to people not getting vaccinated. Scientists then developed a new type of vaccine, which just contained parts of the bacteria that the immune system would recognise, called antigens. This vaccine didn’t cause as many undesirable side effects, so people were happy to be vaccinated. The target coverage of 90%, to prevent outbreaks of whooping cough, is now being reached in most countries.
However, despite the high numbers of people getting the whooping cough vaccine, we have recently started to see outbreaks of whooping cough around the world. There have been some big outbreaks over the last fifteen years, including in the UK in 2012. There is another outbreak going on in New Zealand right now, which started in late 2017. Unlike the measles, these outbreaks can’t be fixed just by encouraging more people to get vaccinated, because most people already are vaccinated.
So, why are those who have already been vaccinated still getting infected?
Scientists all around the world are researching whooping cough and B. pertussis, to work out what is going wrong. It is well known that no vaccine is 100% efficient in preventing the disease, but the numbers of people catching whooping cough is unexpectedly high. There are currently two main factors thought to be contributing to this. Firstly, the new vaccine seems to produce immunity which wanes over time. This means that people are protected from whooping cough immediately after being vaccinated, but after a few years, they are vulnerable to infection again. And secondly, we think B. pertussis may have mutated so that the antigens we use in the vaccine don’t match those in the bacteria which are infecting people. Together, these two factors mean that more people are catching whooping cough and passing it on to other people whose vaccine has worn off, or who haven’t been vaccinated, leading to outbreaks.
For most people, the return of whooping cough just means having an irritating cough for a few months. But for very young babies who haven’t been vaccinated yet or people with weakened immune systems, whooping cough is bad news. It can cause more serious illnesses like pneumonia, sometimes leading to permanent airway damage or even death.
What can we do?
For now, we can help to prevent vulnerable people from catching whooping cough by getting vaccinated ourselves. Many countries recommend that people who are going to be around vulnerable individuals, like the parents and siblings of newborn babies, get a whooping cough booster vaccine. It may wear off after a few years but, in the meantime, we won’t infect people who aren’t immune themselves. In the long run, scientists are working hard to figure out how to make the vaccine better, by studying how our immune system reacts to the vaccine, looking at the DNA of the bacteria to see if anything has changed, and trying to develop a completely new vaccine. Hopefully, one day soon, we can make whooping cough a disease of the past (again).