Pertussis (whooping cough) is a conundrum. It is a disease that was described hundreds of years ago and the bacteria that causes it (Bordetella pertussis) isolated in 1906. We have had vaccines for about 80 years but this disease is defiant in the face of human immunity.
I wanted to address some misconceptions about pertussis vaccines. Seven key points in case you cant be bothered with the detail.
- Pertussis is horrible
- Pertussis has killed heaps of New Zealanders
- Pertussis is not always obvious – you can’s always tell who has it
- The vaccines work well
- The vaccines are not perfect and both symptomatic and asymptomatic people can carry and transmit the infection.
- The current pertussis vaccines are incredibly safe, even if you are pregnant
- Best group to be in is the vaccinated group
Pertussis is horrible
The disease is a major public health problem and until widespread vaccination was one of the most common childhood illnesses and a significant contributor to childhood death. Yes it can be a horrible disease. The bacterial toxin basically paralyses the little hairs on of the respiratory tract (cilia) and causes it to become inflamed, this interferes with the clearance of mucous and stuff. The cough can last over three months. I won’t take up real estate here to describe the symptoms, you can see an adult with pertussis here and a baby with pertussis here. As any normal person can see, pertussis is a totally shit disease and while there is a spectrum of severity not everyone has a mild dose.
There is no cure for pertussis. Getting antibiotics really early in the infection can cut it off short but this needs to be really early. Once you are away coughing there is nothing that can be done. Not every disease you get protects you from getting it again and pertussis is one of those diseases. The an adult can have pertussis 2-3 times in their life.
Examination of the studies that described duration of protection acquired by natural infection with pertussis over one-hundred years suggest multiple disease-causing infections are likely. See below the estimate of protection from natural infection varies!
Pertussis has killed heaps of New Zealanders
- 1873 – 356 deaths
- 1883-4 – 246 deaths
- 1907 – 307 deaths
Pertussis is not always obvious
While people infected with pertussis may have no symptoms, others may have a cough that is non-specific – in that there is no ‘whoop’ or paroxysm. A summary of studies across many countries at different times indicates that among adults presenting to their doctor with a cough, the bacteria B.pertussis is often isolated.
Pertussis is common in Auckland adults and children presenting to the GP with a cough. In 2011 a study tested 226 individuals presenting to their Auckland GP with a cough lasting more than 2 weeks. There were both children aged 5-16 and adults aged 17-49 included. The study was conducted just prior to a major epidemic (so when pertussis rates were low). Among the coughing adults 10% had evidence of recent pertussis infection and this was 17% in the children. There were no distinctive clinical symptoms to distinguish these cases from coughs with other causes.
You cant always tell who has pertussis.
The vaccines work well
For a NZ flavor, we did a study a few years ago to measure the effectiveness of our childhood pertussis vaccination programme. We used the entire population of infants and children from 2006-2013 to access all cases then randomly selected 20 matched controls for each case. We found that in infants up to four-years of age the vaccine was 85-89% protective and in children aged 4-8 years of age the booster dose was 88-93% effective. Not perfect but not bad either.
If pertussis vaccine is given during pregnancy between about 13- and 38-weeks’ gestation, the baby is protected against pertussis for the first 2-3 months of life. This protection is around 90%. The first study to demonstrate this incredible protection is from the UK. Heads up from our NZ study, which we are currently in the midst of: We are looking at all pregnancies from 2013 to 2018 (~350,000) and in NZ the vaccine looks very effective at preventing pertussis in the youngest babies too young to be vaccinated.
The vaccines are not perfect
While having the disease naturally does not bullet proof you against another attack, the vaccine induced protection is less so. It appears that the older vaccines (whole cell) provided longer lasting protection that then newer acellular vaccines (like we have used here in NZ since 2000).
Here the estimates of protection against pertussis offered by older whole-cell vaccines varies up to 14-years.
Here the estimates of protection against pertussis offered by the newer acellular vaccine varies up to 10-years
Also, the vaccines do not appear to prevent people picking up the bacteria and transmitting it to others. This was finally demonstrated in a non-human primate where by baboons, who develop pertussis just like humans, were vaccinated against pertussis and became subsequently protected. However, when they were exposed to the infection they were able to transmit it to their non-vaccinated friends. This is one of the reasons we have so much trouble controlling pertussis.
Both symptomatic and asymptomatic people carry and transmit the pertussis infection.
The acellular pertussis vaccines are incredibly safe
There is a vast amount of data on the safety of acellular pertussis vaccines (which are formulated with tetanus and diphtheria vaccines at a minimum) and it makes for quite a boring read. The most serious adverse events that have been shown to be causally related to acellular pertussis vaccine are extremely rare. In infants these are: High fever, occasionally associated with a febrile seizure (0.5/100,000), persistent crying (0-0.2/100), getting non-responsive for a period (14-62/100,000). Click here for WHO rate sheet.
In pregnancy there are no safety signals so far. The most recent systematic review of the safety of pertussis vaccine in pregnant women included 47 high quality studies and found no evidence for adverse pregnancy, birth, or neonatal outcomes. Here is a link to the 2018 systematic review, and a 2019 review.
We carried out a study on safety in pregnancy and used all pregnancies in NZ (mums and bubs) that occurred in 2013 (68,550 women and their babies). We looked at all hospital outcomes for mother and baby and compared the risks between vaccinated and unvaccinated. We did not identify any safety concerns. Here is the article for the maternal outcomes, and here is the article for the infant outcomes.
Despite the fact that pertussis vaccines are not as effective as some other vaccines, they prevent a huge number of cases of disease. The best group to be in by a long shot is the vaccinated group, no matter what study you look at.