News & Views: Beyond the Obvious — Benefits of Measles Vaccine

Measles vaccine, which used to be heralded as a savior among parents, now suffers from concerns about its safety. Although suggestions around MMR vaccine and autism have been thoroughly discredited with data from various researchers on several continents, some parents remain concerned about a potential link. Limited experience with and knowledge about measles may also make some complacent about the potential severity of this disease, particularly less frequently mentioned characteristics, such as the immune suppression that follows infection. Further, some have heard the false notion that measles disease helps prevent cancer. Together, these ideas may lead parents to believe that forgoing measles vaccination is the safer choice.

So, what should parents know when considering MMR vaccine?

Measles disease: More than meets the eye

Young parents, and even some young healthcare providers, may be familiar with the rash, fever, “pinkeye,” and ease with which measles spreads, but they may not realize that measles virus suppresses the immune response to other pathogens for a period of time following infection or that it can establish a long-term persistent infection, ultimately resulting in death.

Immune suppression caused by measles infection was demonstrated in the 19th century by von Pirquet, who found that responses to tuberculin tests were diminished following a bout with measles. It has since been established that the virus infects various cells of the immune system, including T and B cells, which decrease in circulation early during infection. Although the quantity of these cells tends to recover quickly following disappearance of the rash, immunity is not as readily re-established. It is theorized that the cells lost during the initial drop in numbers induce a type of “immune amnesia,” as T and B cells against other pathogens are infected and killed. So, while the numbers of T and B cells recover, they do not protect against the same breadth of infections.

Just how long it takes to recover, immunologically speaking, has been studied in different ways. Mina and colleagues, used population-level data and mathematical modeling, to determine that the effects could last as long as two to three years. However, Gadroen and colleagues, completed a population-based, matched-controls cohort study and found that when they compared previously vaccinated, measles-infected individuals with vaccinated individuals who did not get measles, those with disease suffered an increased rate of other infections during the first year after diagnosis. When they compared all measles-infected individuals, not just those who were vaccinated, the increased frequency of infections was seen for five years, although the greatest effects were found in the first year after measles infection.

Persistent infection with measles virus, while rare, can occur if the virus infects neurons or astrocytes in the brain. While the individual appears to recover from measles, the ongoing replication of the virus eventually results in the development of subacute sclerosing panencephalitis, or SSPE, which results in increasing loss of neurologic capacity and is, ultimately, fatal. SSPE typically becomes apparent seven to 10 years after seemingly recovering from measles infection, and is more likely when infection with measles occurs before the age of 2.

Measles disease and cancer?

Some people who fear the MMR vaccine have argued that people should not get vaccinated because having measles disease protects against cancer. This is a false claim that likely arose from a misinterpretation of ongoing studies over the past 20 years experimenting with the measles vaccine virus strain, called Edmonston. Because some human cancer cells are selectively targeted for destruction by measles virus, researchers have been exploring ways to infect cancer cells with measles virus, making them vulnerable to attack and destruction by cells of the immune system. Called measles virotherapy, this technology is being tested in a small number of clinical trials.

To date, the technology has not proven successful enough to become part of widely used treatment protocols. However, scientists continue to learn more about when and how this approach may work. They have determined that the best responders have certain types of tumors and a particular immune cell repertoire, including high levels of measles-specific memory T cells and no circulating measles-specific antibodies. Previously vaccinated individuals are better suited to meet these criteria than unvaccinated individuals, so contrary to anti-vaccination claims, vaccination is the better choice.

Because immunization invokes measles antibodies, scientists have identified three ways to circumvent existing antibodies when clinically treating cancer with measles virus. These include:

• Transiently depleting measles-specific antibodies prior to treatment
• Putting measles virus in carrier cells so it is not inactivated before reaching the tumor cells
• Changing the virus so that it is not recognized by existing measles antibodies

The most advanced to date is the carrier cell model, which is currently being tested at the Mayo Clinic to treat patients with ovarian cancer.

The researchers involved in this line of research recently published a statement article encouraging vaccination and explaining the technology.

In sum: Measles vaccine decisions

In conclusion, parents who are considering forgoing measles vaccination for their children should be aware of the consequences. Specifically:

• Not getting measles vaccine increases the likelihood that during an outbreak, their child will be infected because of the highly contagious nature of the disease.
• Infection with measles leads to illness that lasts about a week and involves fever, itchy and watery eyes, cough, congestion, irritability and rash, as well as long-lasting immune suppression that remains for months or years after the infection, making the child more susceptible to other infections.
• In very rare cases, particularly if the child is infected before 2 years of age, a persistent infection can occur.
• On the other hand, vaccination is highly effective and safe.
• And, in fact, the type of measles virus used in the vaccine is being explored as a possible cancer treatment tool.