Well, that didn’t take long, did it?
The potential association between a Zika virus outbreak in Brazil and a startling increase in the serious birth defect microcephaly had barely reached public consciousness and anti-vaxxers were spinning a startling new conspiracy theory: the rising incidence of microcephaly in Brazil is caused, not by Zika virus infection, but by … you guessed it … vaccines!
It’s been a tough decade for anti-vaxxers. Their insistence on a link between vaccines and autism has been thoroughly discredited; their insistence that disease like measles disappeared before the introduction of the vaccine has been thoroughly discredited; their insistence that vaccine preventable diseases like pertussis don’t kill babies has been thoroughly discredited. They desperately need a new conspiracy theory.
[pullquote align=”right” cite=”” link=”” color=”#91D6F1″ class=”” size=””]The anti-vax movement has a perfect record; it has never been right about anything.[/pullquote]
Before going further, I must give credit where credit is due: The anti-vax movement has a perfect record!
That’s right. In the 200+ years since the anti-vaccination movement started, it has never been right about anything!
Apparently, anti-vaxxers are determined to continue their uninterrupted losing streak with the Zika virus conspiracy. The essence of the conspiracy is this: It might look like Zika virus infection of pregnant women causes microcephaly, a severe brain deformity, but it’s really caused by Tdap, the vaccine that prevents tetanus and pertussis. Anti-vaxxers point darkly to the fact that, following in 2015 Brazil began routinely offering pregnant women Tdap in the 3rd trimester to protect newborn babies from getting pertussis.
The Zika/Tdap conspiracy follows the usual anti-vax tropes. In “All manner of ills”: The features of serious diseases attributed to vaccination, authors Leask, Chapman and Robbins explain that diseases attributed to vaccines share a variety of common features:
- Unknown cause
- Apparent risk in incidence
- Face value biological plausibility
- Dreaded outcomes
- Close proximity to vaccination
All the elements are present in the Zika tragedy. Although the working hypothesis is that the increase in cases of microcephaly are cause by infection with Zika virus, that has not yet been definitely established. There has been a rise in incidence of microcephaly in Brazil. It is biologically plausible. The outcome of microcephaly is usually severe intellectual and physical disability. And the birth of babies with microcephaly may have followed third trimester vaccination with Tdap.
But there’s no evidence that Tdap vaccination in pregnancy leads to microcephaly and considerable evidence that it does not.
Third trimester Tdap vaccination has been instituted around the world. Why is the increased incidence of microcephaly restricted to areas where Zika virus is endemic?
Microcephaly is a defect that originates in the early weeks of pregnancy when the brain is forming. How could an event in the third trimester have any impact on a process that was complete months before?
In contrast, there is considerable evidence that Zika virus infection of pregnant women is the likely cause:
There are a variety of viral illnesses that can cause serious brain defects in the embryo if contracted by pregnant women during the first trimester.
The incidence of Zika virus infection has been rising in Brazil. This is not the first Zika outbreak in the world, but it is the largest. Moreover, there is evidence that the Zika virus has mutated as it traveled around the globe since its discovery in Africa in 1947. The viral mutations appear to allow it to infect humans with greater ease.
Zika virus has been isolated from babies born with microcephaly and from pregnant women who gave birth to microcephalic babies.
Moreover, the conspiracy theory makes no sense in light of the actions of world health authorities:
If microcephaly were caused by Tdap, wouldn’t health authorities be trying to hide the issue not publicize it?
Why would health authorities issue travel advisories to countries where Zika is circulating if they knew that the cause was not Zika?
Why would the US spend money on the development of a vaccine for Zika virus is it’s not the cause of microcephaly?
In summary, there’s considerable evidence that Zika virus infection in the first trimester leads to microcephaly, that the incidence of microcephaly has been rising in parallel with the incidence of Zika infection, and that Zika virus is presented in affected babies and their mothers. There’s absolutely no evidence that Tdap leads to microcephaly and no logical mechanism by which a third trimester vaccination could cause a first trimester defect. Finally, a massive public relations campaign to highlight microcephaly in Brazil makes no sense if health authorities are trying to hide a causal association with Tdap.
But logic has never been the strong suit of anti-vaxxers and I don’t anticipate that there will be an outbreak of logical thinking now. Anti-vaxxers never learn; not matter how many times you destroy their arguments, they keep coming back for more.
