Measles infects & destroys memory & memory-like cells, erasing recollection of past encounters with various microbes & vaccines
As the world scrambled to battle the faceless enemy — the novel coronavirus SARS-CoV-2 — throughout 2020 and 2021, another silent outbreak was taking shape. Nearly 20 million infants missed their first dose of the measles vaccine in 2020 as the global vaccination rate fell from 86 per cent in 2019 to 84 per cent, according to UNICEF.
The previous figure had already been stagnant for a while and remains significantly lower than the 95 per cent global target.
This, according to scientists, has mounted a concern: Immune amnesia caused by measles. While this concept is relatively new — discovered only in 2012 — it explains why the unvaccinated, once infected with measles, have long-term immune suppression and heightened susceptibility to unrelated infections.
Immune amnesia means the contagious infection can wipe out the immune system’s memory of other illnesses. The children who recover from measles may become susceptible to other pathogens they may have had protection from before they had the measles virus.
Vaccination drives, owing to the novel coronavirus disease (COVID-19) pandemic, were hit the most in Southeast Asia and Eastern Mediterranean regions of the World Health Organization (WHO), while 24 campaigns in 23 countries across the globe were delayed in 2020, putting 93 million people at risk.
This has been recorded as the largest increase in missed vaccination in two decades, setting the stage for a rise in outbreaks of a highly infectious disease.
This was preceded by record figures in 2019 in the past 23 years — at over 800,000 total cases and more than 20,000 deaths across all WHO regions. The lowest ever cases were reported just four years prior to this, in 2016. Experts cite missed vaccination as the reason for the spike.
At 149,796, the number of measles cases recorded in 2020 was significantly lower than it was in 2019. A drop in infections was recorded across all WHO regions that year.
Africa reported 618,595 cases in 2019 and 115,364 in 2020; the Americas reported 21,971 cases in 2019 and 1,548 in 2020; the Eastern Mediterranean reported 18,458 cases in 2019 and 6,122 in 2020; Europe 106,130 cases in 2019 and 10,772 in 2020; Southeast Asia 29,389 cases in 2019 and 9,389 in 2020; the Western Pacific 78,479 cases in 2019 and 6,601 in 2020.
Many believe this is the calm before the storm. Since measles transmits via air, strict lockdown measures, mask mandates and social distancing triggered by COVID-19 pandemic did play a crucial role in curbing the spread.
However, routine surveillance was also interrupted during the lockdown. The number of samples sent for testing dropped to the lowest (122,517) in a decade in 2020, according to the WHO Global Measles and Rubella Laboratory Network.
What is immune amnesia?
Several experts have highlighted concerns about a measles outbreak taking a threatening shape in a post-COVID-19 world.
David N Durrheim, a conjoint professor of public health medicine at the University of Newcastle noted in his paper published February 2021:
The COVID-19 pandemic distracted attention from the worst global measles pandemic of this century. The decreased measles case reporting in 2020 is falsely reassuring and was occasioned by a combination of immunity after the large-scale 2018–2019 outbreaks.
Rik De Swart, associate professor of neuroscience at Erasmus University Medical Center, Netherlands, in conversation with Down to Earth, said: “Measles will linger around and when it gets the opportunity, it will find the pockets of people who are without immunity. We have a realistic danger now, that we may see an explosive measles outbreak in the near future.”
Immune amnesia caused by measles is a more worrying concern, said scientists.
“It was recently demonstrated that MeV (measles) infects and destroys memory and memory-like cells, thus erasing the recollection of past encounters with various microbes and vaccines. How this phenomenon manifests itself in different individuals and how it may be remedied, fully or partially, remains to be explored,” Mansour Haeryfar, professor of immunology at Western University, Canada told Down To Earth.
Measles is a respiratory disease; one would expect the virus to bind itself with receptors in the lungs. A group of Japanese scientists in 2002, however, discovered it does so on the immune system’s cells.
This was further explored a decade later by international researchers, including Swart. Upon attaching a green fluorescent protein to track the measles virus in macaque monkeys, it was understood how memory B and memory T cells of the immune system can be attacked following measles infection.
The virus causes immune suppression at the same time it causes immune activation. This is called the measles paradox. Once infected with measles, you are highly unlikely to get it again.
Immune amnesia and COVID-19
What does an unprecedented rise in measles cases, a significant drop in vaccination and surveillance alongside immune amnesia mean during COVID-19 times?
A study titled Immune amnesia induced by measles and its effects on concurrent epidemics published in June 2021 noted: “When measles vaccination policies are relaxed, the expected herd immunity for any secondary infectious disease X can be lost owing to the proliferation of individuals affected by immune amnesia. In particular, under its effects, the epidemic threshold is shifted so that severe outbreaks can take place even under extensive X vaccination.”
Given issues surrounding low vaccination rates, no doses for children in several countries and a mutating virus, complications surrounding herd immunity against COVID-19 as a plausible reality remain.
Swart said the risk may not be that high on an individual level, it may potentially cause a risk of damaging the level of immunity to COVID-19 on a population level.
“I am convinced that measles can impact COVID-19 caseload and death rate. We do have indications from several epidemiological studies that death rates, in some cases, increase during a long period after a big measles outbreak,” he said.
Haeryfar underlined another salient point. “It is also noteworthy that a percentage of healthy individuals who have never contracted COVID-19 in the past appear to harbour memory cells that are cross-reactive to SARS-CoV-2. This means they have memory cells in their body that can detect certain SARS-CoV-2 antigens simply because they have been infected with antigenically similar coronaviruses in the past.”
On one hand, measles is a disease that remains largely prevalent in children. On the other hand, COVID-19 mostly does not infect infants severely, but there have been a significant number of serious or even fatal pediatric cases.
However, a study on the impact of a 2019 measles outbreak on COVID-19 in Samoa, an island nation in Oceania, argued for a “potential increase in morbidity and mortality” among children since that is the age group severely impacted by measles.
The study also noted how children play an important role in transmitting COVID-19 and have a higher viral load in respiratory tracts than adults.
It argued: “While children may be more likely to be asymptomatically infected (by COVID-19), reflected by a low proportion of all cases being children a background of a compromised immune system induced by recent measles infection may change the age-specific epidemiology in countries with recent, widespread measles transmission.”
This is the first part in the two-part series on measles and immune amnesia during COVID-19. Check out this space for more
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