Blog coach Carolien | Measles

Natural measles infection whips-out your immunological memory

A four-fold increase in number of measles cases was reported in Europe in 2017 and was largely due to people refusing to be vaccinated (https://doi.org/10.1136/bmj.k795). Measles symptoms include runny nose, cough, high fever, watery eyes, small white spots on inside of the cheeks (Koplik’s spots) followed by a rash. However, the more severe symptoms of measles virus infections, including ear infections, blindness, swelling of the brain (encephalitis), diarrhoea and severe respiratory infections like pneumonia, can be life threatening. After the introduction of a safe and effective measles vaccine in 1963, the numbers of measles infections started to decline rapidly. Furthermore, a >95% vaccine coverage prevents spread of the measles virus in the population. The remaining 5% is reserved for the very young or people with a weak immune system (e.g. as a result of chemotherapy) who cannot be vaccinated. Ironically these groups are at the highest risk for having the most severe symptoms. Fortunately, they are protected by the vaccinated people around them (herd immunity).

The severe symptoms seem to be largely erased from our collective memory, as younger generations have not been confronted with full blown measles outbreaks in their lifetime. Is the measles vaccine becoming a victim of its own success?

Among the main reasons for parents to not vaccinate their children are: 1) religion and 2) because they believe that a measles infection will induce a better immune response than the vaccine. But is this last point true? Does a measles infection really induce better immunity as compared to a measles vaccine?

A recent paper on this subject appeared in the renowned science journal Nature Communications (https://doi.org/10.1038/s41467-018-07515-0). The study was performed by a talented young scientist and virus-fighter Bri Laksono, PhD student at the Viroscience Department of the Erasmus MC in the Netherlands. She was happy to share her expertise with Viruskenner.

The paper described a unique study, conducted in the Netherlands, that gave new insights in a phenomenon that researches have tried to explain for many years: an increased risk for severe infections in the years following a measles virus infection.

Bri explains that she investigates what happens to our body when it is infected by the measles virus and what happens after the virus is cleared from our body. The focus of the current study was to understand how measles virus affects our immune system.

So how did they do this? The Dutch Orthodox Protestant community does not vaccinate children for religious reasons. During the 2013 measles outbreak, Bri and her colleagues collected blood samples from unvaccinated children before and after they were infected with the measles virus. This way they could measure the effects of a measles virus infection on the cells of the immune system, especially the white blood cells (Figure 1). White blood cells are known to patrol the body for infectious pathogens (e.g. viruses and bacteria), attack these pathogens and clear the infection. When you encounter a virus for the first time the white blood cells act relatively slow and you get sick. However, the cells that were able to recognize this specific virus will form a “memory population”. These memory cells are an improved version of the white blood cells, so the next time you get infected with the same virus they will react faster and stronger and you will not get sick. The older you are, the more exposure you will have had to different pathogens (either by infection or vaccination) and the more memory cells you have to fight different types of infections. Bri explains that their study showed that the measles virus infects those improved memory cells and that the memory population for pathogens you encountered in the past largely disappears. Meanwhile, your body makes a big memory population of white blood cells that only recognizes the measles virus. This means you are protected for life against the measles virus, but at the same time your immune system has no memory of previous virus or bacterial infections. You have to restart building these memory populations. This is the biological explanation of why we observe more infections with different viruses and bacteria up to two years after a measles infection. Your immune system lost its ability to respond quickly, explains Bri. It is currently unknown how long it will take for the immune system to fully restore its immunological memory. Further studies are also needed to demonstrate if and how the original memory populations are restored. One option is that you need to be reinfected with pathogens from the past to restore your memory responses, says Bri.

In conclusion, natural measles infections induce a stronger immune response to measles than vaccination, but this happens at the expense of losing immune memory to other pathogens you were previously exposed to. Meanwhile, the vaccine induces good and protective immune response to measles, also protecting you for life, at no cost. The measles vaccine does not infect and kill our memory white blood cells, explains Bri.

Finally, I asked Bri if she had any advice for those of you who are considering becoming a real virus-fighter:

“Stay curious. Read a lot. Debate a lot. Learn a lot. Question a lot. Find people who will nurture your curiosity and help you learn more. Respect those people and never break their trust. Make them proud.”  

And because Bri is originally from Indonesia, I asked her if she had special advice for our Indonesian virus-fighters:

“Do not let things get you down. I know how some people encourage others to think critically, but at the same time force them to accept everything without questions. Do not let your gender or age discourage you from pursuing your dreams. Challenge yourself and others, but do so with the utmost respect.”

Link to measles infographic, that explanes this study