Is there a related protection for the measles vaccine?

Is there a related protection for the measles vaccine?
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The Journal of Infectious Diseases, jiz381,

published: November 01, 2019

Measles is rampant again, unfortunately, in Europe and the United States [1, 2]. For this reason, it is important to know the correlates of protection against measles, to evaluate the susceptibility of individuals and the population, including all those who had previously been vaccinated.

Defining a vaccine protection related is not easy, as I have learned over the years. In 2001, I covered the topic for the first time, trying to simplify it through some definitions and criteria [3]. Later I realized that nothing is simple, as has been noticed since time immemorial [4]! The reasons for this lack of simplicity are varied, including the lack of standardization of essential immunological tests, the multiplicity of antibody and immune cell functions, and the many ways in which these functions interact. In addition, additional doses and number of doses also count in the correlates estimates.

Despite these appalling circumstances Bolotin et al, in the current issue of The Journal of Infectious Diseases [5], they reviewed the data of the protective correlates through the measles vaccine. In this field, for a long time relied on a study by Chen et al on a measles epidemic [6], in which blood samples were taken from the subjects before vaccination and after a subsequent wave of measles.

The conclusion drawn from that study was that 120 mIU of antibodies to the measles virus, based on the results of an enzyme-related immunosorbent assay (ELISA) assay, were correlated with clinically diagnosed measles protection.

Although that was, and is, a useful number, its accuracy has not been confirmed for several reasons.

First, the antibody level was measured by an ELISA, the dosage of which does not take into account the antibody function in measuring the antibodies themselves.

Antibodies perform multiple functions, including neutralization, prevention from binding to the body, and increased activity of natural killer cells. Furthermore, the responses of cells to the measles virus are not clearly defined, and for some diseases these responses add up to the antibody response. Therefore it is important to look again at measles protection correlates, which Bolotin et al have tried to do.

In the nineteenth century, Panum [7] he acknowledged that the measles virus infection naturally contracted in the Faroe Islands conferred permanent immunity against the disease, and, in fact, that observation can still be considered true today. However, the vaccine generates an attenuated infection, and it does not happen that the antibodies remain permanently elevated in the vaccinated. This situation is responsible for re-evaluating the long-term effectiveness of the measles vaccine [8].

Although the vast majority of measles vaccinates remain positive forever, as with the mumps vaccine, the circulation of new measles virus genotypes can be important. Genotypes B3 and D8 are currently in circulation, and these viruses are not neutralized as well by antibodies against the vaccine genotype (e.g. genotype A) as by antibodies that counteract new species. [9]. More importantly, a minority of vaccinates lose antibodies over time and thus become susceptible to wild measles virus infection.

Cherry and Zahn recently showed that 11% of measles cases in California occurred in vaccinated people who received two doses of the vaccine [10]. A study carried out in Spain observed that between 2003 and 2014, 132 measles cases were observed in those who had received two doses of the vaccine [11]. In a psychiatric unit for teenagers, one case of measles in an unvaccinated subject led to a 7% contagion rate among his vaccinated contacts, although the disease was mild [12]. A wave involving Dutch medical staff suggested that low levels of neutralizing antibodies in vaccinates correlated with protection failure [13]. Unfortunately, the level of complete protection of neutralizing antibodies is not known.

The possibility that a subclinical infection or a few symptoms with measles virus occurs among vaccinated people should be considered. Although I am not aware of any evidence of virus excretion from vaccinated with some but not all symptoms of measles, isolation of the virus from these patients should be attempted. Furthermore, the reasons for the drop in antibodies in some vaccinated subjects are unknown, and it is necessary to establish new protective correlates based on neutralizing antibodies or other immune functions.

The measles outbreaks that are taking place in Europe and the United States could be useful if samples were obtained from those who expose themselves to contact before it is or is not infected. The scientific community should take advantage of the current situation brought by vaccine resistance and ignorance of vaccines to better define the correlates of measles immunity.

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