Vaccines and Narcolepsy: What We Learned Since the H1N1 Vaccine
We first started to understand the connection between narcolepsy and our immune system after the 2009 H1N1 pandemic. Doctors saw a surge of new narcolepsy cases after people recovered from the H1N1 swine flu, and 1 of the H1N1 vaccines used in northern Europe increased the risk of developing narcolepsy.1
We now know that infections from viruses and bacteria can trigger narcolepsy in people with certain genetic markers. Plus, we learned that vaccines can also cause narcolepsy by triggering the same autoimmune reaction.1
No vaccines used in the United States have caused narcolepsy, and the benefits of vaccines almost always outweigh the risks. However, as we prepare for the COVID-19 vaccine, it is important to learn from past events and understand the risks.
What is the connection between narcolepsy, infections, and vaccines?
People with narcolepsy have a faulty barrier between sleep and wake. This leads to sudden attacks of sleep during the day and other symptoms. We now know that an autoimmune reaction can trigger narcolepsy. This happens when your immune system attacks your body instead of foreign invaders like viruses and bacteria.2,3
Most people with narcolepsy have a mutation in a gene called HLA-DQB1. This gene helps the immune system tell the difference between your own proteins and proteins made by foreign invaders. People who have a certain version of the HLA-DQB1 gene, called HLA-DQB1*0602, seem to be more likely to have narcolepsy.4,5
In the brains of people with narcolepsy, the immune system attacks cells that produce a hormone called hypocretin. Hypocretin regulates sleep and energy. Without enough hypocretin, it is difficult to stay awake.3,6
Proteins in certain viruses look similar to proteins on brain cells that produce hypocretin. When people with HLA-DQB1*0602 are exposed to these viruses, the immune system can accidentally attack these cells. Vaccines that contain pieces of these viruses can also trigger this reaction.4,6,7
Not all viruses and vaccines have proteins that cause this reaction. In fact, no vaccines regularly used in the United States cause narcolepsy.
What happened with the H1N1 vaccine?
The connection between narcolepsy and our immune system became clearer after the 2009 H1N1 influenza pandemic. China reported a surge of narcolepsy cases among children after the pandemic. Most of these cases occurred in people who did not receive an H1N1 vaccine, so narcolepsy seemed to be a side effect of H1N1.4,8-10
A rise in narcolepsy cases also occurred in people from countries that administered a certain H1N1 vaccine. This vaccine, called Pandemrix, was used mostly in northern Europe. It was never used in the United States.11-13
Pandemrix caused narcolepsy in about 1 out of every 16,000 children who were vaccinated. The rate varied a great deal by region. Countries with people who have a smaller genetic risk for narcolepsy – areas where many do not have the HLA DQB1*0602 gene mutation, for example – did not see a surge of narcolepsy cases from Pandemrix.6
We still do not know exactly why Pandemrix increased the risk of narcolepsy. Other similar vaccines did not increase narcolepsy risk in other countries. Experts think it could be linked to either the viral protein in Pandemrix, other components in the vaccine, or the timing of the vaccination program in northern Europe.4,5
Even still, the H1N1 vaccination saved many lives by preventing the spread of disease. Because H1N1 itself is a risk factor for narcolepsy, vaccination may have reduced the frequency of H1N1-induced narcolepsy in many areas of the world.10
Should I be worried about the COVID-19 vaccine?
Fears of a similar thing happening with COVID-19 vaccines have been raised, especially in northern Europe. There is specific concern because some COVID-19 vaccines are using the same “adjuvant” as Pandemrix. An adjuvant is a vaccine ingredient that helps strengthen the immune response. However, other vaccines that used the same adjuvant (the “AS03” adjuvant) did not increase narcolepsy risk.4,14,15
The most important takeaway from the H1N1 vaccine is that the side effects of the infection give us clues for the side effects of the vaccine. If we knew H1N1 could trigger narcolepsy, we could have screened for it as a side effect of vaccines. For COVID-19, we know what side effects to monitor when vaccines are introduced. One example of this is an autoimmune condition that looks like Kawasaki disease, which may be triggered in the same way as narcolepsy.4
Other lessons from the H1N1 vaccine include:4
- Conducting clinical trials in every age group
- Performing large studies after vaccines are introduced
- Planning who to vaccinate first and how fast to vaccinate a population
- Quickly providing treatments to people if side effects appear
Vaccines are one of the best and safest ways to prevent the spread of disease. Serious side effects are extremely rare. However, no vaccine is 100 percent effective and 100 percent safe. The benefits of vaccination usually far outweigh potential risks. When a contagious disease like COVID-19 can cause serious long-term complications, a vaccine is one of the best ways to keep you and your loved ones healthy.
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