Measles is a highly contagious virus that initially causes a runny nose, sneezing and fever and later leads to a blotchy rash starting on the face and spreading to the rest of the body. The majority of the people infected will recover, but measles can cause diarrhea and vomiting, which can lead to dehydration, middle ear infection (otitis media), which can lead to hearing loss, or pneumonia or potentially fatal encephalitis (swelling in the brain).

When people get an infection, their immune system produces antibodies to fight the infection. After the body gets rid of the infection, special immune cells remember that specific pathogen and help the body mount a faster defense if that same pathogen invades the body again. But not with measles. The virus reboots children’s immune system and the “amnesia” makes them vulnerable to other pathogens that they might have been protected from a previous infection.

In one study [M.J. Mina et al., Science, 366:599–606, 2019], measles infection in unvaccinated children in a community in the Netherlands was associated with up to a 70% decline in antibodies to other pathogens following infection. After cases of severe measles, unvaccinated children lost a median of 40% (range 11-62%) of their already existing pathogen-specific antibodies and after a case of mild measles, children lost a median of 33% (range 12-73%) of these pre-existing antibodies.

On the other hand, kids vaccinated retained over 90% of their antibody repertoires over the same period. The researchers examined blood from 77 unvaccinated children infected with measles in the Netherlands during a 2013 outbreak and compared these samples with the blood of 115 uninfected children and adults using the VirScan system, a tool that detects antiviral and antibacterial antibodies in the blood. Samples were taken prior to and after measles infection.

The team found that rather than a simple loss of total IgG, the most common type of antibody found in blood circulation, there is a restructuring of the antibody repertoire after measles. This is the first study to measure the immune damage caused by the virus and is further evidence for the “immune amnesia” hypothesis (that by depleting antibody repertoires, measles partially obliterates immune memory to previously encountered pathogens).

The same investigators also infected macaques with measles and monitored their antibodies against other pathogens for five months. The measles-infected monkeys lost 40–60% of their antibodies against pathogens they have previously encountered suggesting that measles infection wipes out long-lived plasma cells in the bone marrow that can create pathogen-specific antibodies.

A separate, independent team published a related study [V. N. Petrova et al., Sci Immunol, 4:2019] showing that measles infection causes incomplete reconstitution of the naïve B cell (not exposed to an antigen) leading to immunological immaturity and compromised immune memory to previously encountered pathogens due to depletion of memory B lymphocytes that persist after measles infection. The study provides a clear biological explanation for the observed increase in childhood deaths and secondary infections several years after an episode of measles.

These two new studies emphasize the importance of measles vaccination and suggest that given these findings, booster shots against other illnesses, such as hepatitis or polio, may be necessary for children infected with measles.

In 2017, the World Health Organization (WHO) reported 110 000 measles deaths globally, mostly among children under the age of five. The actual number of people infected with measles is most probably higher given that the WHO only collects data on cases confirmed through lab testing or clinical visits excluding thousands who do not seek medical attention.

With the global trend of vaccine hesitancy, skeptical parents are refusing to get their children vaccinated due to false concerns about their safety. These 2 new studies add strong evidence and undoubtedly confirm what scientists and public health experts have known all along: measles bad, vaccines good. This time let’s remember… let’s not have amnesia that measles can cause immune amnesia.