The New Measles Epidemic – Concerns For Pregnancy
The recent well-publicized outbreak of measles in the United States has alarmed physicians and health officials. The choice of many parents to forgo vaccinating their children has not only endangered these children but all non-immune children and adults. In addition, measles is still common in many parts of the world including some countries in Europe, Asia, Africa and the Pacific. World travelers continue to bring this disease into the United States. Of particular concern are the risks faced by women who are either attempting pregnancy or who are already pregnant.
Measles, also known as rubeola (not to be confused with rubella or German measles) is a highly contagious disease caused by an RNA virus belonging to the Paramyxoviridae family. Humans are the only known host for this virus. It is so contagious that
90 percent of people who are not immune to the disease will become infected if exposed to a measles carrier. The virus’s virulence is highlighted by the fact it can remain behind and infect individuals for a couple of hours after an infected person leaves a room. Measles is transmitted via droplets with the highest incidence of infection in late winter and spring. Once infected, an individual will be infectious for approximately eight days. Ten to twelve days after exposure, an infected individual will progress to the prodromal stage with 2-3 days of fever, malaise, anorexia, and the classic triad of cough, conjunctivitis, and coryza. Near the end of this prodromal stage, the pathognomonic sign of measles, Koplik’s spots lasting 12 to 18 hours appear as blue-white lesions on the inner surface of the mouth. The prodromal stage is followed by a high fever and a maculopapular, erythematous rash which begins on the head and face and spreads out and down to the hands and feet.
Up to 30% of infected persons suffer complications from measles with the most common being diarrhea (8%), otitis media (7%) and pneumonia (6%). Encephalitis is a rare complication (0.1%) of measles and is the leading cause of death from this virus. Exposure to measles during pregnancy may cause serious adverse effects for both the mother and fetus. In a 1993 study that followed the medical course of 58 pregnant women with active measles infection, 15 (26%) developed pneumonia of which 2 (13%) died. While measles has not been associated with birth defects, it increases the risk of pregnancy loss and pre-term birth. If contracted late in pregnancy, viral transmission to the fetus is likely to cause a serious infection of the newborn. These newborn infections are associated with high mortality rates and serious morbidity primarily from sub-acute sclerosing panencephalitis (SSPE).
The presence of an infection is confirmed with a blood test that either measures the antibody response using a serological assay or detects the presence of the measles virus in clinical specimens by viral culture. Human normal immunoglobulin (HNIG) is recommended for non-immune pregnant women exposed to the virus within six days of exposure. While this will not prevent measles, it is effective in reducing measles-related symptoms and sequelae if infection occurs. Also, if the maternal exposure is close to delivery, HNIG may help reduce the risk of the newborn contracting measles.
The Advisory Committee on Immunization Practices (ACIP), the American Congress of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), and the American Academy of Family Physicians (AAFP) recommend the use of the MMR (M-M-R-II®, Merck, Whitehouse Station, NJ) vaccine in the prevention of measles, mumps, and rubella. The production of the monovalent forms of this vaccine (measles – ATTENUVAX®, mumps – MUMPSVAX®), and rubella – MERUVAX®) vaccines (Merck) was discontinued in 2008. There is no medical indication to avoid the current trivalent form of this vaccine. The reduction of injections required from 3 to 2 reduces delays in achieving immunity and increases compliance. The MMR vaccine contains live attenuated viruses and thus is contraindicated in pregnancy. While the theoretical risk for fetal complications as a result of the inadvertent immunization of pregnant women with MMR is 1.6%, there is no documented case of this vaccine ever having induced congenital fetal abnormalities. The CDC, for this reason, does not recommend termination of a pregnancy after MMR exposure. While Vaccination with MMR is well tolerated, some of the more common side effects include a fever lasting several days that begins 5 to 12 days after vaccination, a rash, arthritis, and arthralgia. The MMR vaccine should be avoided in patients have recently received or are scheduled to receive antibody containing blood products (e.g. Rhogam) and in those with a history of a severe allergy to vaccine additives (neomycin and gelatin). In addition, patients who are immunocompromised or are being treated with any immunocompromising agents as well as those with a history of seizure of any etiology should avoid vaccination.
The current recommended schedule for vaccination is to obtain the first dose between 12 to 15 months of age to be followed by a second dose at age 4 to 6 years. For eligible non-pregnant women, the two-dose MMR series is strongly advised and is administered 28 days apart with at least one month before conception. The measles component of the MMR vaccine is effective in 95% to 98% of individuals after one dose and >99% after two doses. While vaccine efficacy is similar to rubella, the mumps component has only a 64% to 95% rate of seroconversion after one dose and 88% to 95% after the second dose. Despite receiving a two-dose childhood vaccination, up to 10% of adults will lose immunity to rubella and 20% of adults will lose immunity to measles. Thus, approximately 20% of women of reproductive age are at risk for measles exposure and the associated consequences.
The standard of care in the U.S. is not to assess the seroconversion of measles or mumps, but only that of rubella. However, since the long-term efficacy of rubella is greater than measles, there is a risk that a person found to be immune to rubella may, in fact, have unknowingly lost their immunity to measles. In the face of a local measles outbreak, it would be prudent then to test specifically for measles immunity regardless of the rubella status. If a patient is found to be non-immune to rubella or measles, MMR vaccination is recommended either one month prior to conception or at completion of an ongoing pregnancy. Breastfeeding is not a contraindication to vaccination nor will it alter the child’s immunization schedule.
The increase prevalence of parents not vaccinating their children coupled with world travel from measles-rich areas has led to an increase in local outbreaks of measles in non-immune individuals in the United States. It would be prudent to remain vigilant of these outbreaks in the context of treating women of reproductive age. Measles outbreak activity in the US can be followed at the CDC’s measles website.
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