Pertussis notification and vaccination status in context

Across the globe it is known how important the pertussis (whooping cough) vaccine is in preventing both infection and severity of infection with Bordetella pertussis.

Along with vaccines for diphtheria and tetanus, then polio (1950′s), measles, mumps, rubella (1960′s) the Australian pertussis vaccine has contributed to an astonishing 99% reduction in deaths from vaccine preventable disease. Just after the turn of the century pertussis, diphtheria and tetanus vaccines alone had saved over 70,000 lives whilst the population had almost tripled since their inception. Since then pertussis vaccination alone has saved around another 10,000 Australian lives.

From the World Health Organisation, to national or state health authorities across developed nations to your local doctor, the evidence is compelling. Although anyone can catch pertussis it is babies under 12 months who are most vulnerable to infection. The disease can cause disability and death in the unvaccinated. Whilst immunisation provides antibodies to fight pertussis, it does not provide “magical protection”. For that you need chiropractors or other practitioners of alternatives to medicine.

Immunisation against pertussis does mean:

  • A significantly reduced chance of being infected
  • A significantly reduced severity of infection if infected
  • Protection of unvaccinated individuals that one may come into contact with
  • Low levels of community infection with high levels of immunisation

Pertussis epidemics follow on from reduction in immunisation across the community, leading to a drop in herd immunity. The present epidemic Australia is experiencing began in Byron Bay, an area with very low immunisation rates, and then spread to other areas of low immunisation. From the backyard of Meryl Dorey’s anti-vaccination lobby group the seeds for this epidemic were sown a decade ago. Brynley Hull and Peter McIntyre wrote in January 2003 [page 12]:

Although immunisation coverage has greatly improved over the past five years in NSW, and many areas have reached coverage targets, there are areas in NSW where the level of registered conscientious objection to immunisation is great enough to affect immunisation coverage, as measured by the ACIR. One such area is northern NSW, and the Byron Bay SLA in particular, where the rate of conscientious objection is one of the highest in the country.

Despite the crystal clear science and undoubted success of immunisation, movements against all vaccines have grown. They have kept pace with internet driven conspiracy theories, imaginary diseases, imaginary cures and new age beliefs. The most successful currency used by those opposed to scientific success is ignorance and misinformation.

An excellent example regarding pertussis vaccination is that many people incorrectly believe all vaccines, with the exception of influenza, provide lifelong immunity. With pertussis, vaccine induced immunity wanes over time and as noted above whilst it reduces the chance of infection, it is not an impervious shield. Antivaccination lobbyists have taken advantage of this to infer that the pertussis vaccination schedule itself has failed. First, we have ignorance – the expectation that immunity is lifelong. Then follows misinformation.

For example as debunked here more than a few times, figures describing vaccination levels and notification of infection are frequently misused by the Australian Vaccination Network to falsely refute the efficacy of immunisation. Yet these clumsy attempts are piecemeal and misleading. Time and again infection notification and vaccination status is highlighted and infused with qualities that serve to misinform. Placing figures in context yields a very different picture which, given that they seek to deny international trends that have existed for decades, is not surprising.

The question, or challenge if you will, is about the veracity of the pertussis vaccination schedule. Thus we must take care to ensure we elucidate notifications related to full immunisation as per the schedule. Take the following table of children between 0 – 4 years old, diagnosed with pertussis:

Pertussis notification by vaccination status 0-4 years, Australia August 2011

We see that a total of 9,333 notifications have been tabulated. 5,296 or 56.7% are fully vaccinated.

986 are partially vaccinated. 800 are not vaccinated. 754 are ineligible for vaccination. This gives us a total of 2,540 or 27.2% who are not fully vaccinated.

1,497 or 16% are unknown.

Do these figures reflect infection in the community? No, they reflect the vaccine status of children diagnosed.

Firstly as the table informs us “fully vaccinated” does not necessarily conform with fully vaccinated under the National Immunisation Program. Ineligible cases between 6-8 weeks of age that had received one dose in 2009 are included in “fully vaccinated”. Both these facts artificially inflate the “fully vaccinated” category.

Next we must accept that this table underestimates the actual number of infections in the community. The National Notifiable Diseases Surveillance System relies on a passive surveillance system which does not capture every case of pertussis in the community.

Which raises the question. Who is not making notification? Can we infer anything about the vaccination status of those not recorded in the above table? If so, does this help us understand the figures in the table better? As a matter of fact, yes.

Do these figures reflect the efficacy of pertussis vaccination? In other words, is this telling us that there are over twice as many infected children in our community who have been vaccinated (56.7%), than those who have not been fully vaccinated (27.2%) and thus reflect low vaccine efficacy? No.

Far more children are vaccinated against pertussis than those who are not. 95% vs 5% in fact. Even with greatly reduced chance of infection the sheer numbers of vaccinated children mean that “fully vaccinated” will dominate notifications. These figures also reflect the greater likelihood of parents who vaccinate to take their child to a GP and follow through with reporting, and also reflect the likelihood of conscientious objectors to avoid a GP and to not follow through with reporting.

For example a USA study published in Vaccine in December last year showed that parents who do not vaccinate their children are four times more likely to take their child to a chiropractor than a conventional doctor. In Australia we already know that chiropractors are vocal antivaccination proponents with strong links to antivaccination lobby groups such as the Australian Vaccination Network. Many chiropractors in Australia actively mislead consumers on the topic of vaccination making impossible claims, actively deriding vaccination.

But we can do much better than this and begin to build a profile of parents who refuse vaccination and later choose conscientious objection. Five days ago Australian Doctor reflected on the study:

A US survey found parents who refused childhood vaccinations were four times more likely to have sent their youngest, school-aged child to a chiropractor than parents of vaccinated children. Parents who conscientiously objected to school immunisation requirements were also more likely to have strong concerns about vaccines, to distrust local doctors and to have had one or more births in a non-hospital, alternative setting. [...]

Are naturopathic and complementary healthcare providers reinforcing parental concerns and ‘anti-vaccine’ opinions or promoting exemptions, or are they providing healthcare without emphasizing vaccinations?

The pattern emerging is one of anti-conventional medicine, reinforced by alternatives to medicine masquerading as “complementary healthcare”.  For our purposes we must now accept that unvaccinated children may be up to four times less likely to visit a GP when ill with pertussis. This means they may be up to four times less likely to appear as a notification. Regardless of exactly how many unvaccinated children are missed, we can see with confidence that the total is skewed away from highlighting unvaccinated children.

Thus the 8.6% of unvaccinated children noted in the table above (n=800) is possibly a significant underestimation. As parents who do vaccinate are more likely to visit a GP and report diligently, the total is additionally skewed toward the fully vaccinated. What this actually means regarding community impact is best captured in this post written by a mother whose vaccinated child was infected by an unvaccinated child who had been sent to school.

Now comes the fascinating aspect. “Unknown”. What does this mean? Really? For whatever reason, somewhere along the line the child’s vaccination status is not recorded at all, is recorded and fails to make it to the final notification table or is lost to genuine confusion or poor record keeping.

However if parents are not registered on the ACIR as conscientious objectors or as completing their children’s vaccination schedules they are also listed as “unknown”. Thus the following from Brynley Hull and Peter McIntyre is compelling [bold mine]:

Additionally, the proportion of conscientious objectors on the [Australian Childhood Immunisation Register] ACIR is likely to be an underestimate of the proportion of parents who don’t immunise because they disagree with immunisation, particularly in more economically advantaged areas. There are some non-immunising parents who ‘object to registering’, and they will refuse to complete any government-provided form.

“Refuse to complete any government-provided form”. Such as those that question the immunisation status of one’s child? That also is where a significant number of “unknown” cases have their genesis.

In tandem with our emerging profile of anti-conventional medicine beliefs driving the decision to not vaccinate and combined with the observation that CO’s are likely to contribute to the “unknown” category by not registering on the ACIR, we are able to make a strong inference that unvaccinated out-rate vaccinated in this category.

Whilst it is impossible to make outright factual quantified claims and rewrite that table, we may conclude that placed in the context of community trends it gives a less than reliable indication of infected subjects within the community. What it does give us is a snap shot of the vaccine status of notifications. Placed in context those notifications appear to be skewed away from unvaccinated and toward vaccinated subjects.

The most significant reason is the overwhelming numbers of vaccinated children in the community. Although appearing as a notification they have a far less severe case of pertussis and are unlikely to suffer disability or death. Other reasons for this would appear to be the intentional avoidance or substitution of conventional medicine, diagnosis and reporting of vaccination status by those in denial of vaccine efficacy.

Of course, people will use these figures to attack the overwhelming evidence in support of vaccination. That’s just what eccentric parent Greg Beattie has tried. It’s simply gobsmacking to read his misleading claim that only 11% of pertussis infections aren’t vaccinated. Actually it’s only 8.6%.

But the point to be made is whilst only 5% of 0-4 year olds aren’t “fully vaccinated” they make up a disproportionate 27.2% of infection notifications. Unsurprisingly his novel mathematics have been dealt with unceremoniously by A Drunken Madman.

There is no debate here. Pertussis vaccination saves lives.

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