Regardless of your stance, vaccination against measles is one of the safest, most successful and cost-effective public health interventions so far in history. Prior to mass vaccination campaigns, around 4 million people in the US got measles every year, 500 of whom died, 48,000 were hospitalized, and 4,000 suffered serious brain swelling; it’s far from a trivial infection. But thanks to immunization campaigns, cases have dropped by more than 99%.
But it turns out that this jab does far more than just protect you against infection with the measles virus; it protects you from other infectious diseases. How? According to a new study, measles puts your immune system into a state of amnesia for up to 3 years after infection, leaving you vulnerable to a whole host of other potentially fatal diseases. Vaccine hesitancy therefore doesn’t just threaten community immunity against measles, but also an abundance of other microbes.
Scientists have known for some time that measles profoundly dampens the immune system, attacking cells that retain a memory of past infections. However, this was assumed to be short-term, possibly only lasting a few weeks or months. But since the introduction of mass vaccination campaigns, scientists have observed some striking effects which suggested that there is more to the story. For example, mass measles immunization in some of the world’s poorest countries has reduced overall childhood deaths by a staggering 90%. Furthermore, declines in mortality from infectious diseases after receiving the vaccine can last up until a child is 5 years old.
Although scientists aren’t sure of the exact mechanism behind this apparent protective effect, recent work on monkeys started to shed light on this mystery. After the anticipated drop in protective white blood cells following infection, their immune systems quickly bounced back within a few weeks. However, a large number of these new cells would have arisen from the abundance of measles-specific cells that resulted from infection. So while the immune system seemed to be replenished, the original, broad repertoire of cells could have been replaced by one almost entirely directed against measles, resulting in a so-called “immune amnesia.”
To examine this idea further, Princeton scientists began probing data on measles cases and deaths from other infectious diseases, pre- and post-mass vaccination campaigns, in three countries: the US, UK and Denmark. More specifically, they wanted to see if there were any relationships between measles cases and deaths among children.
As described in Science, they found that measles infection affected resistance to other diseases for up to 3 years. Furthermore, they found the tight relationship between measles incidence and deaths from other infectious diseases during this vulnerable period still occurred after measles vaccinations were widely used, indicating that the vaccine protects against more than just measles virus.
“In other words, reducing measles incidence appears to cause a drop in deaths from other infectious diseases due to indirect effects of measles infection on the immune system,” lead researcher Bryan Grenfell explained in a news-release.
To make the data more watertight, they also examined whooping cough data, which doesn’t suppress the immune system. This failed to turn out any links between whooping cough and mortality from non-measles infectious diseases, suggesting the finding is indeed specific to measles.
Since the study produces indirect, rather than direct, evidence for the protective effect of the measles vaccine, further studies are warranted to confirm their findings. However, the researchers are already planning on exploring potential immunological mechanisms further.
[Via Science, Science and Princeton University]