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Rubella Vaccination - Continued

The dates of vaccination and estimated dates of confinement were known for all of the 119 susceptible women who had full-term pregnancies (Figure 1). Forty-four women (37%) were vaccinated within 1 week before to 4 weeks after conception, the period of presumed highest risk.

Serologic evaluations (rubella HI titers and specific IgM on cord or neonatal blood specimens) were performed on 104 (86%) of the 121 infants whose mothers were susceptible. One normal-appearing infant had a rubella-specific IgM antibody titer of 1:8 in cord blood and a corresponding HI titer of 1:128. The maternal titer was also 1:128. Retesting of cord blood and testing of a 2-month follow-up specimen run simultaneously showed an expected decrease in maternally derived Hl antibody over the 2-month period from a titer of 1:64 to 1:16, suggesting that subclinical infection may not have occurred. The infant had no evidence of defects compatible with CRS at birth or at the 18-month and 29-month follow-up examinations. Further follow-up sera could not be obtained to document persistence or disappearance of HI antibodies.

Blood studies were also obtained on 150 of the 241 infants born to mothers whose immune statuses were unknown at the time of vaccination. Subclinical infection was documented in two infants. One infant had a rubella-specific IgM antibody titer of 1:16 in cord blood. Both mother and infant had HI titers of 1:32 at the time of birth; the infant had a persistent HI titer of 1:32 at 4 months of age. This infant had no evidence of defects compatible with CRS at birth or at the 10-month and 17-month examinations. A serum specimen was not obtained at the follow-up visits. The second infant had a persistent HI titer of 1:8 at 3 months of age, suggesting that there had been subclinical infection. This infant was diagnosed as normal at the 3-month follow-up visit.

While none of the 121 infants born to susceptible women had defects compatible with CRS, two infants did have asymptomatic glandular hypospadias. However, both had negative FIGURE 1. Interval between receipt of rubella RA 27/3 vaccine and estimated date of conception, in weeks, among susceptible women with live births United States, January 1979 through December 1983

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Rubella Vaccination Continued rubella-specific IgM titers (less than 1:4) in cord blood at birth. A 6-month follow-up serum was available for one of the infants; he had a rubella Hl antibody titer of less than 1:8.

Twenty-five susceptible women elected to have induced abortions (Table 1). Thus, rubella virus has now been isolated from the products of conception in one (3%) of 32 cases involving susceptible women (19 cases reported to CDC and 13 from the literature) (4-6). Reported by Surveillance and Investigations Section, Surveillance, Investigations, and Research Br, Div of Immunization, Center for Prevention Svcs, CDC. Editorial Note: Since 1971, CDC has maintained a register to monitor and quantitate the risks to the fetus following exposure to attenuated rubella vaccine virus. Data are obtained through reports from physicians and from state and local health departments, as well as directly from women vaccinated either within 3 months before or 3 months after conception. The patients are followed prospectively to determine the outcome of pregnancy. In 1979, when RA 27/3 rubella vaccine replaced the other rubella vaccines, concern was raised that it might have greater fetotropic and teratogenic potential than earlier vaccines. As with the other vaccines, data collected so far show no evidence that the RA 27/3 rubella vaccine can cause defects compatible with CRS.

Forty-four (37%) of the 119 susceptible mothers were vaccinated with RA 27/3 vaccine during the highest risk period for viremia and fetal defects (1 week before to 4 weeks after conception) (7,8). Neither those infants nor any others were born with CRS; therefore, the observed risk of CRS following rubella vaccination continues to be zero. The theoretical maximum risk for the occurrence of CRS in this group of 121 children, however, based on the 95% confidence limits of the binomial distribution, may be as high as 3.0%. (If the 95 infants exposed to other rubella vaccines are included, the maximum theoretical risk is 1.7%.) This overall maximum risk remains far less than the 20% or greater risk of CRS associated with maternal infection with wild rubella virus during the first trimester of pregnancy (3) and is no greater than the 4%-5% rate of birth defects in the absence of exposure to rubella vaccine (9,10).

These favorable data are consistent with the German experience cited at the International Symposium on the Prevention of Congenital Rubella Infection recently held at the Pan American Health Organization. A total of 91 susceptible women vaccinated with either the Cendehill or RA 27/3 strain of vaccine gave birth to normal-appearing infants. Limited data presented at the symposium from the United Kingdom also support the CDC observations.

The occurrence of any congenital defect following maternal vaccination deserves careful analysis and follow-up. Two infants born to susceptible mothers had asymptomatic glandular hypospadias. While hypospadias has been noted in CRS cases (11,12), there are no data to suggest that glandular hypospadias should be considered a CRS-associated defect. In any case, neither of the two infants in question had serologic evidence of rubella virus infection. Ten other infants born to mothers of unknown immune status (eight) or known to be immune (two) at the time of vaccination had some type of defect (13). However, none of the defects were compatible with CRS and serologic testing, when done, did not confirm rubella virus infection.

While no CRS-like defects have been noted, it is clear that rubella vaccine viruses, including the RA 27/3 strain, can cross the placenta and infect the fetus. Approximately 1%-2% of infants born to susceptible vaccinees had serologic evidence of subclinical infection, regardless of vaccine strain (3). On the other hand, while the rubella virus isolation rate from the products of conception for the RA 27/3 vaccine is only 3% (1/32), the rate of virus isolation for Cendehill and HPV-77 vaccines is 20% (17/85) (3). These data indicate that the risk of placental or fetal infection from RA 27/3 vaccine is minimal.

In view of the data collected through 1983, the Immunization Practices Advisory Commit*These proceedings are to be published in Reviews of Infectious Diseases.

Rubella Vaccination - Continued tee (ACIP) continues to state that: (1) pregnancy remains a contraindication to rubella vaccine tion because of the theoretical, albeit small, risk of CRS; (2) reasonable precautions should be taken to preclude vaccination of pregnant women, including asking women if they are pregnant, excluding those who say they are, and explaining the theoretical risks to the others; and (3) if vaccination does occur within 3 months of conception, the risk of CRS is so small as to pery be negligible; thus, rubella vaccination of a pregnant woman should not ordinarily be a reason to consider interruption of pregnancy. The patient and her physician, however, should make the final decision (14).

Since the inception of its vaccine-in-pregnancy register, CDC has encouraged reporting of all such cases. Because of the increasing number of cases reported to CDC, the experience with known susceptibles is becoming well defined. Therefore, CDC now encourages reporting only cases involving women known to have been susceptible at the time of vaccination Laboratory services for serologic determination and culture of placental and fetal tissue wil continue to be available at CDC for susceptible cases that are reported. References 1. CDC. Rubella vaccination during pregnancy–United States, 1971-1981. MMWR 1982:31 am

477-81. 2. CDC. Rubella and congenital rubella - United States, 1983. MMWR 1984;33:237-42, 247. 3. Preblud SR, Stetler HC, Frank JA Jr, Greaves WL, Hinman AR, Herrmann KL. Fetal risk associated with rubella vaccine JAMA 1981:246:1413-7.

(Continued on page 373.

TABLE I. Summary-cases specified notifiable diseases, United States

Disease

June 30,
1984

26th Week Ending

Modian 1979-1983

July 2,
1983

Cumulative, 26th Week Ending
June 30,
July 2,

Median 1984

1983 1979-1990

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Acquired Immunodeficiency Syndrome (AIDS)
Aseptic meningitis
Encephalitis: Primary (arthropod-bome

& unspec.)

Post-infectious Gonorrhea: Civilian

Military
Hepatitis Type A

Type B
Non A, Non B

Unspecified
Legionellosis
Loprosy
Malaria
Measles: Total*

Indigenous

Imported Meningococcal infections: Total

Civilian

Military
Mumps
Pertussis
Rubolla (German moaslos)
Syphilis (Primary & Secondaryl: Civilian

Military
Toxic Shock syndrome
Tuberculosis
Tularomia
Typhoid fover
Typhus fever, tick-bomo (RMSF)
Rabios, animal

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TABLE II. Notifiable diseases of low frequency, United States
Cum, 1984

Cum 1984 Anthrax

1

Plague Botulism: Foodborne 6 Poliomyelitis: Total

2 Infant (Calif. 3)

47
Paralytic

2 Other

3 Psittacosis (N.Y. City 1, Utah 1) Brucellosis (Kans. 1. Miss. 1, Tex. 1. Colo. 1, Calif. 1) 49 Rabies, human Cholera

Tetanus (Upstate N.Y. 1)

22 Congenital rubella syndrome

Trichinosis (Pa. 1)

39 Diphtheria

Typhus fever, flea-borne (@ndemic, murine)

9 Leptospirosis

8

(Tex. 1, Calif. 1) "Four of the 104 reported cases for this week were imported from a foreign country or can be directly traceable to a known international imported case within two generations.

TABLE III. Cases of specified notifiable diseases, United States, weeks ending

June 30, 1984 and July 2, 1983 (26th Week)

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TABLE III. (Cont.'d). Cases of specified notifiable diseases, United States, weeks ending

June 30, 1984 and July 2, 1983 (26th Week)

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