Measles Virus Clobbers the Immune System
We once hoped that measles would follow smallpox into extinction. From hundreds of thousands of cases in 1963 when the vaccine was introduced many countries became measles free. No longer. Measles caused more than 100,000 deaths worldwide in a recent year according to The World Health Organization and that number has recently increased. American Samoa, where levels of vaccination are less than 41% is enduring an epidemic. Almost 5000 cases have occurred in a population of about 200,000 and 70 people have died, mostly were children under five. Samoa closed down—no schools, no sports, no government offices open, no tourism. People stay home and if a house has active cases, they indicate that with a flag. Vaccination by the local health authorities with resources from The Centers for Disease Control is proceeding.
The measles virus is a miserable little thing. Like hundreds of other viruses, we know the sequence of its genome (only six genes) and what role each gene performs. Its power starts with the fact that it is a respiratory virus and is efficiently transmitted by a cough. (Imagine what might have happened if Ebola virus has been transmitted by a cough.) If you are on a plane or a ride at Disneyland with an infected coughing person, you have a high chance of drawing a measles virus into your lungs.
Happily, immune cells patrol your lungs; B cells, T cells and macrophages have evolved to deal with invaders and to activate the immune system. If you have had the full vaccine your immune cells are prepared and that is the end of it.
If not, measles virus has the advantage because it has evolved specific ways to infect those roving immune cells and to sabotage their protective efforts; a few hours after inhaling the virus, macrophages or B cells in your lungs could be producing millions of new viruses, even if you do not immediately feel sick.
Infected immune cells wander out of the lungs into the circulation. The next target is the skin, where the virus copies itself. When the immune system detects these infected cells, inflammation results, causing the defining reddish rash. The rash fades about 10 days after infection and the patient usually recovers.
But this is not where our story ends. Physicians and parents have noticed that after a measles infection children are often susceptible to other diseases, for as long as two years. A paper from an international consortium based at Harvard Medical School and the University of Amsterdam was published in Science Magazine on November 1, 2019, explains why.
After any viral infection, the body’s immune system responds by producing specific antibodies that bind to and inactivate the virus, one set of antibodies for each virus. After the infection is over, the response subsides, but certain cells, called memory B cells are banked, probably in the bone marrow and continue to produce antibody at a low level to provide continuous immunity.
After a case of measles, antibodies that protect a child against chickenpox, mumps or many other viruses, disappear from the blood, for months or even years. During that time children are vulnerable to infections that their immune systems had seen before would have snuffed out.
Think of accumulated antibodies to a host of different viruses or bacteria as a bank account. People can increase their bank account by vaccination or by successful recovery from an infection. This bank may be a person’s most important asset. That asset, however, can be hacked and emptied by the measles virus, reducing the patient to immunological poverty.
To ask whether measles virus eliminates antibodies that neutralize other viruses, we must find a population of children who do not get vaccinated and who will get the disease by natural means. We must also get their permission.
As it happens, there are three villages in the Netherlands that follow a form of Protestant orthodoxy that precludes vaccination. Parents and students in three local schools were asked by mail if they would be willing to participate in a study. There were 73 positive responses. The regulatory background for such studies, both Dutch and American, is strict but since this experiment requires a few milliliters of blood before and after a child gets measles it does not pose a great risk.
In a tour-de-force of molecular biology, bioinformatics, statistics and international organization, the consortium of researchers showed that after a measles virus infection, kids had a much lower diversity of circulating antibodies and were less protected against many serious viruses than they had been. Measles vaccine (MMR) did not reduce immunity. Unvaccinated kids who never got measles (only a few) also did not lose antibody diversity.
Not taking the MMR vaccine exposes a child to a lot more than measles, mumps and rubella. The results explain a lot and suggest other uses for the technology (called VirScan), and raise a lot of interesting questions.
I think I can make this paper interesting to non-scientists. I will try on Monday January 13 at 6PM at the Norfolk Hub as part of a general discussion of vaccines and disease that we are having. Call the Norfolk Hub to reserve a free seat.
Richard Kessin, PhD in Professor Emeritus of Pathology and Cell Biology and Columbia University’s Irving Medical Center. He lives in Norfolk and can be reached at Richard.kessin@gmail.com.