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Long vax — rare neurologic syndrome after COVID vaccines


A new paper was published showed that people who experienced rare long-term adverse events after a COVID-19 vaccine often had neurologic symptoms. These adverse events, sometimes called “long vax,” are rare and have a far lower incidence than long COVID-19.

Some anti-vaccine activists have pounced upon this study to issue vague or even strongly worded claims about the safety of the COVID-19 vaccines. However, what the study shows is quite the opposite of that.

“Long vax,” which has similar symptoms to long COVID, has been recognized by scientists for a while. This new paper addresses what some of those symptoms are. However, and I will repeat this several times, the incidence of long vax is much lower than long COVID-19, and it does not mean that the vaccine is either unsafe or ineffective.

I will help the reader examine this new paper, and review the relevant data and conclusions.

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New long vax paper

In a paper posted on 10 November 2023 on the preprint server medRxiv, Harlan Krumholz, MD, of Yale School of Medicine in New Haven, CT, and colleagues, reviewed surveys of 241 people who self-reported a post-vaccination syndrome (long vax). This was not a random sampling of 241 people, but a group that has self-reported having long vax and what they claim were their symptoms.

This study surveyed 241 adults who self-reported PVS after COVID-19 vaccination and who joined the online LISTEN study from May 2022 to July 2023. Individuals that had been diagnosed with long COVID were excluded from this study.

Participants completed surveys from November 2022 through July 2023, an average of 595 days post-vaccination. From a list of 96 symptoms, the participants were asked to identify health conditions they had as a result of the COVID-19 vaccines. They also reported their self-perceived health status on a 5-point scale of excellent, very good, good, fair, or poor.

Before I look at the data, I want to warn the reader that this study has not been peer-reviewed. For the most respected journals, peer reviewers examine the data, the analytical methodology, and the conclusions before it can be published in those journals. According to some recent research, about 77% of medRxiv articles eventually have been published in peer-reviewed journals, but that means about one-quarter of them do not. This does not mean that this article on long vax is bad or not, it’s just that it hasn’t received a full peer review.

With that out of the way, let’s take a look at the data from this study:

  • 55% received the Pfizer-BioNTech (Comirnaty) vaccine and 37% had the Moderna (Spikevax) shot. The remainder had the JNJ and Novavax vaccines.
  • 34% said they had SARS-CoV-2 infection at least once.
  • The five most common symptoms were exercise intolerance (71%), excessive fatigue (69%), numbness (63%), brain fog (63%), and neuropathy (63%).
  • Long vax symptom onset occurred within a median of 3 days of the index vaccination. Symptoms began after the first, second, third, and fourth (or more) vaccinations for 44%, 33%, 14%, and 9% of participants, respectively.
  • The median number of symptoms that the participants attributed to long vax was 22.
  • Overall, 44% rated their current health as fair or poor.

Critical analysis

Another study, published in May 2022 in medRxiv, describes rare neurological symptoms that occur post-COVID vaccination. I think there is adequate evidence that long vax might be a real syndrome after vaccination.

However, I am not a big fan of surveys of individuals for biomedical research because it is filled with bias and relies upon the memories and beliefs of the patients. For example, it is entirely possible that their symptoms were not related to the COVID-19 vaccine but to other issues. We would need full medical histories of each patient, which would be best done with studies that use vaccine databases like the Vaccine Safety Datalink (VSD) and the Clinical Immunization Safety Assessment Network (CISA). They give researchers access to the medical history of each patient allowing them to better describe a potential causal link between the COVID-19 vaccine and long vax.

Furthermore, this study does not describe, nor was it powered to describe the predicted incidence of long vax in individuals who received the COVID-19 vaccine.

Humans have a tendency to misuse incidence data for vaccines — some people will round up adverse events, which are minuscule, to 100% risk, and round down extremely high effectiveness rates to 0%.

The risk of long COVID-19, which has similar symptoms, is around 10%. We don’t know what the risk of long vax is, but it is far lower than 10%.

You might ask, “Well, why don’t we have a perfect vaccine that has 0% risk of long vax?” That is a legitimate question, but the problem is that there is nothing perfect in medicine. It is always a balance between risk and benefit. There might be a 0.5% risk of long vax, but if you get COVID-19 without vaccination, you have a higher than 10% risk of long COVID-19.

I think this new research identifies some of the parameters of long vax, but it in no way provides data as to the risk for the syndrome. It is just a data set that helps us identify what some of the symptoms are but does not give any credible evidence that COVID-19 vaccines are unsafe.

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Michael Simpson

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