Autism and Immunization - A Strange Puzzle

Yearly autism reports in VAERS

Note on post title - the “strange puzzle” was the data patterns in the yearly reports in VAERS.

Vaccine Adverse Event Reporting System (VAERS)

The FDA and CDC support a voluntary reporting system for vaccine adverse events, named Vaccine Adverse Event Reporting System (VAERS).  A subset of population adverse events are reported to VAERS.  The number of adverse events in a population can be estimated by comparing the reports in VAERS to the reports collected in clinical trials. The proportion of reports is expressed as under-reporting factor (URF).  Adverse events are expected to occur within a population at background frequency rates, usually expressed as number of cases per 100,000 individuals per year.  Post immunization, the reports to VAERS are predicted to be skewed towards higher reports immediately following immunization with decreased likelihood of reporting as time increases – this is referred to as reporting bias.

Measles, Mumps, and Rubella vaccine

In 1998, Wakefield et al. [Lancet 1998;351:637-41] published with subsequent retractions a flawed article linking the measles, mumps, and rubella (MMR) vaccine may predispose to behavioral regression and developmental disorder in children.

Figure 1. MMR autism and autism spectrum disorder adverse event reports in VAERS

The number of autism reports in VAERS increased with higher reports starting in 2000; note the unusual spike in 2009.

Multiple vaccines

From 2000 until 2010, the number of autism reports in VAERS increased for multiple vaccines:

Vaccine names: MMR – measles, mumps, and rubella; HIBV – Haemophilus influenza type B; DTAP – diphtheria, tetanus, and pertussis; VARCEL – varicella vaccine (chickenpox); IPV – inactivated polio vaccine; PNC – pneumococcal vaccine; and OPV – oral polio vaccine.  Note that the oral polio vaccine (OPV) was stopped in the year 2000 in the United States and replaced with inactivated polio vaccine (IPV).

These autism and autism spectrum disorder adverse event reports in VAERS do not fit a background population model. The patterns may exhibit excess reporting following the Wakefield et al. article (retracted) and perhaps suppressed reporting. Variability between vaccine lots cannot be excluded. Whe Wakefiled article was retracted by Lancet in 2010. The average by vaccine looks like:

It appears that the fraction of cases being reported to VAERS was impacted (reporting bias) upwards following the Wakefield article in 1998 and decreased after the retraction in 2010. So, most of the data patterns could be accounted for my shifts in reporting bias. But, this still leaves the peak of reports in 2009 as unexplained. This still leaves a lot of children with reports in VAERS.

Children with Dravet syndrome, also known as severe myoclonic epilepsy of infancy, present with their first seizure following vaccination.  Mutations in the sodium channel protein type 1 subunit alpha (SCN1A) gene are frequently found in these children.

A large number of genetic variants (copy number variations, duplications, deletions, translocations, inversions, and mutations) are associated with autism spectrum disorder including mutations in the genes chromodomain helicase DNA binding protein 8 (CHD8), neuronal voltage-gated sodium channel, type 2, alpha Na_V1.2 (SCN2A), katanin catalytic subunit A1 like 2 (KATNAL2), and other genes. 

Are the parallels with autism spectrum disorder and Dravet syndrome with stress events like vaccinations sometimes acting like triggers? A case series of autism spectrum disorder individuals selected by onset immediately following vaccination including genetic evaluation of known genetic variants could evaluate this hypothesis.

ASD onset data in VAERS for 24 hours post vaccination

Multiple studies examine a window of time (many days) for comparing two groups for evidence of correlation; the longer the window of time, the more background events are included. Focusing upon the first 24 hours minimizes the loss of signal against background events. For VAERS, reporting bias is an issue with each subsequent day having diminished reports; again, focusing upon a window of the first 24 hours minimizes this bias - but it is still there in the data. Finally, the number of vaccinations administered varies by vaccine. To examine the data and create estimates for the larger population, the VAERS reports on fever (pyrexia) is used. For young children, this is an easily obtained quantative measurement free of most reporting biases. In the following table, the last row represents the percentage of day 0 ASD reports over fever reports. In other words, for X% of children who were vaccinated and developed a reported fever, how many can also be expected to also report autism spectrum disorder adverse event with onset within 24 hours of vaccination. Often, multiple vaccinations are administered at the same time - literature exists indicating increased adverse events occur for some combinations.

Table - Day 0 onset autism spectrum disorder adverse events post vaccination in VAERS.

VAERS data from 1990 to August 4, 2023.  Percentage of these adverse events compared to the pyrexia (fever) adverse event reports.  Vaccine names: MMR – Measles, Mumps, and Rubella virus vaccine (live), HIBV – Haemophilus B conjugate, DTAP – Diphtheria and Tetanus toxoids and acellular Pertussis, HEP – Hepatitis B virus, DTP – Diphtheria and Tetanus toxoids and Pertussis, and IPV – inactivated Polio vaccine.

Table - Day 0 for ASD and pyrexia adverse events reported from 2011 to August 4, 2023 in VAERS.

Additional vaccine names: HEPA - hepatitis A vaccine and VARCEL - Varivax-Varicella virus (live).

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