Impact of Revaccinating Children Who Initially Received Measles Vaccine Before 10 Months of Age

(1)

Impact

of Revaccinating

Children

Who

Initially

Received

Measles

Vaccine

Before

10 Months

of Age

Harrison

C. Stetler,

MD, Walter

A. Orenstein,

MD,

Roger

H. Bernier,

PhD,

Kenneth

L. Herrmann,

MD, Barry

Sirotkln,

Dan Hopfensperger,

Ruth Schuh,

MD, Paul Albrecht,

MD,

Alan W. Lievens,

MD, and Philip

A. Brunell,

MD

From the Center for Prevention Services, Centers for Disease Control, Department of

Health and Human Services, Atlanta

ABSTRACT. Two hundred fifty-four infants who had received measles vaccine at <10 months of age were revaccinated at 15 months of age, and their immune

responses were compared with 129 control infants who received their first doses of measles vaccine at 15 months of age. Sera were collected at the time of

revac-cination (study infants) or primary vaccination (control

infants), 3 weeks, and 8 months later and tested for antibody by hemagglutination inhibition (HI),

enzyme-linked immunosorbent assay (ELISA), and cytopathic

effect neutralization (CPEN). Of the 121 study infants

who were initially HI negative, 116 (95.9%) made HI

antibody 3 weeks postrevaccination compared with 126 (99.2%) of 127 control infants (P =

0.19).

Ofthe 63 study

infants with no initial detectable antibody by any of the three tests, 14 (22.2%) had a measles-specific 1gM re-sponse 3 weeks postrevaccination compared with 37 of 50 (74.0%) randomly chosen control infants. By 8 months

after revaccination, the 121 initially HI-negative study

infants were significantly less likely to have detectable

HI antibodies than control infants (52.1% v 97.6%) (P <

.001).

However, 96.7% of these 121 study infants had detectable neutralizing antibody 8 months

postrevacci-nation, an antibody thought to correlate best with

pro-tection. This study confirms the altered immune response

to revaccination in infants first vaccinated prior to 10 months of age; however, the data suggest that most of these infants were successfully primed and are probably protected after revaccination. Pediatrics

1986;77:471-476; measles, vaccine, revaccination, neutralizing antibody, immune response.

The Immunization Practices Advisory

Commit-Received for publication April 10, 1985; accepted Aug 8, 1985.

Reprint requests to Technical Information Services, Center for Prevention Services, Centers for Disease Control, Atlanta, GA

30333.

American Academy of Pediatrics.

tee of the US Public Health Service and the Corn-rnittee on Infectious Diseases of the American Academy of Pediatrics recommend routine measles vaccination at or after 15 months of age. However,

infants

as young

as

6 months of age may be vacci-nated when the risk of exposure to measles is high in a local area; it is recommended that such infants be revaccinated at or after 15 months of age to

ensure

protection

because

seroconversion

rates

are

progressively lower in children younger than 12

months of age.”2

Studies evaluating infants who received measles vaccine at <10 months of age and who were reim-munized after their first birthday have shown that such infants are less likely to have detectable hem-agglutination inhibition (HI) antibody at a later date when compared with control children receiving

only a single

immunization

after

1 year of age.3’4 By

8

or more months later, only about 50% have de-tectable HI antibody compared with more than 90% of control infants. These data suggest that the immune response of some infants vaccinated at <10 months of age is altered and have been interpreted to suggest that they might not be protected against measles, even when revaccinated after 1 year of age. However, these studies included a small number of children and used a limited number of serologic

tests

to assess

the

immune response.

(2)

them to controls who had received their first mea-sles vaccination at 15 months of age.

METHODS

Participants

Study subjects were infants who received single-antigen measles vaccine before 10 months (<300 days) of age and who returned for revaccination at 15 months of age. Initial vaccination occurred from September 1980 through December 1981 at the City of Milwaukee Health Department clinics. Study control infants were chosen from among children 15 months of age who appeared at the same clinics for their first measles vaccination from November 1981 through January 1983.

Field Methods

Infants who were vaccinated initially before 10 months of age were recalled for revaccination at about 15 months of age by the City of Milwaukee Health Department. Two study nurses contacted the parents of such children prior to the revaccin-ation. A preliminary explanation of the study was given and the appointment date made for the re-vaccination. If the parent agreed to the child’s participation, a signed consent was obtained. Con-trol infants were enrolled at the same clinics and were chosen from among children who were to receive their first measles vaccination at 15 months of age.

On the day of revaccination (study infants) or primary vaccination (control infants) the first blood specimen (S,) was drawn. Second (S2) and third (S3) blood specimens were subsequently drawn 3 weeks and 8 months after revaccination (study infants) or primary vaccination (control infants).

Data collected on each subject and control in-cluded identifying information, birth date, sex, race, prior measles vaccination date, present measles vaccination date, history of any previous measles illness, information on adverse events after measles vaccination, and dates when the three blood speci-mens were drawn.

After the S1 blood specimen was drawn, all study infants and control infants received measles,

mumps, and rubella (MMR,1 [measles, mumps

and rubella virus vaccine, live; Merck Sharp & Dohme]) vaccine. A phone call was made to each parent or guardian 2 weeks later to collect data on adverse events and to arrange the 3-week appoint-ment for collecting the S2 specimen. Active follow-up 8 months later was carried out on all infants by the study nurses to obtain the S3 specimen.

Laboratory

Techniques

HI antibodies to measles virus were measured by established techniques5 using heat inactivation and cell adsorption to remove nonspecific inhibitors and agglutinins from test sera, vervet erythrocytes as indicator cells, and Tween-ether-treated measles antigen (a low-passage, wild-like, Edmonston strain of measles virus: seven passages in primary human embryonic kidney cells and seven passages in Vero cells). Sera were screened beginning at a 1:8 dilu-tion. Persons with HI titers <1:8 were considered to be seronegative.

The cytopathic effect neutralization test (CPEN)6 was performed in 96-well flatbottom mi-crotitration trays seeded with Vero cells one day earlier. Serum dilutions and virus were mixed, in-cubated for one hour at 37#{176}C,and inoculated into specified wells on the tray. After seven days of incubation at 37#{176}C,the trays were stained and read microscopically for viral cytopathic effect. The an-tibody titer was determined as the highest dilution of serum inhibiting viral cytopathic effect in 50% or more of wells. Screening started at a 1:4 serum dilution. Persons with CPEN titers of <1:4 were considered to be seronegative.

Measles enzyme-linked immunoassay (ELISA) was performed using the method described by Mur-phy et al.7 Wells of microtitration trays coated with “viral” or “control” antigen were used. Serum sam-ples diluted 1:100 in phosphate-buffered saline-Tween-20 diluent containing fetal bovine and glob-ulin-poor goat serum to decrease nonspecific reac-tivity were added to wells of the antigen-sensitized trays. Antibody bound by the solid-phase antigen was detected with antihuman IgG labeled with a!-kaline phosphatase enzyme followed by washing and incubation with disodium p-nitrophenyl phos-phate substrate. The color reaction was read spec-trophotometrically. The absorbance value for each serum was determined by subtracting the reading ofthe control well from that of the measles antigen-coated well. An absorbance value of <0.056 was considered to be seronegative. This is based on the

results

of sera

collected

from

48 infants between the ages of 15 and 35 months who had neither had measles, been exposed to measles, nor been immu-nized with live measles virus vaccine and who had an HI antibody titer of <1:8.

Measles 1gM testing was performed by standard sucrose gradient ultracentrifugation procedures.8 Persons with 1gM titers of <1:4 were considered to be seronegative.

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Subjects Controls . : 90-4.) > C o

.,-Q 50 -tnt) -‘ 30

L

20 ;- 10 o_

fTT.

HI

had no measurable antibody by any of the three assays on their S, specimens were tested for mea-sles-specific 1gM antibody.

Statistical Analysis

Differences between study and control infants were evaluated using the x2 test with the Yates correction or the Fisher exact two-tailed test. Dif-ferences in mean antibody titers between study and control infants were evaluated using the Student’s t test.

RESULTS

A total of 254 study infants and 129 control infants completed the study (more than 96% of those initially enrolled). There were no significant differences between the two groups with regard to race or sex. None of the infants had a previous history of measles disease. There were no cases of measles reported in Milwaukee from Aug 20, 1980 until after this study was completed. More than 90% of the study infants received their first dose of measles vaccine before 9 months ofage (<270 days), and all control infants were vaccinated between 15 and 23 months of age.

A total of 121 (48.4%) of the 250 study infants with an adequate volume blood specimen for HI testing had no detectable HI antibody at the time of their revaccination (Fig 1). Of the 129 control infants, 127 (98.5%) had no detectable HI antibody prior to measles vaccination (P

<

.001). Study

infants

with HI 1:8 at the time of their revaccin-ation were significantly older (mean age =

7.1

months) at the time of initial measles vaccination

CPEN ELISA HI, . N

& ELISA

Type of Antibody on Si

Fig 1. Percentage of infants with nondetectable anti-body titer at time of revaccination (study infants or

subjects) or primary vaccination (controls).

Abbrevia-tions used are: HI, hemagglutination inhibition; CPEN,

cytopathic effect neutralization; ELISA, enzyme-linked

immunoassay; Si, blood sample No. 1.

than study infants with HI <1:8 (mean age =

6.4

months) (P

<

.001). Seventy study infants (27.7%) had no detectable neutralizing antibody and 89 (41.4%) had no detectable ELISA antibody at the time of revaccination. Of the 215 study infants for whom adequate volume blood specimens were avail-able for all three tests, 63 (29.3%) had no detectable measles antibody by any of these tests as compared with 90.9% of 110 control infants (P

<

.001).

Of the 121 study infants who lacked HI antibody at the time of reimmunization, 116 (95.9%) devel-oped HI antibody 3 weeks after revaccination corn-pared with 126 (99.2%) of 127 control infants (P = .19). Of the five study infants without detectable HI antibody 3 weeks following revaccination, two had detectable low levels of antibody by both the neutralization and ELISA tests, one had no detect-able neutralizing measles antibody but a blood spec-imen of adequate volume was not available for the ELISA test, and two did not have any detectable antibody by any of the tests and are considered true nonresponders. One control infant did not develop HI antibody and also had no antibody detectable by either of the other tests.

The geometric mean antibody titers (HI, CPEN) or mean optical density values (ELISA) for initially HI seronegative infants 3 weeks postrevaccination (study infants) or 3 weeks postprimary vaccination

(control infants) are shown in Table 1. The study infants had statistically significantly higher HI mean titers and ELISA mean optical density values compared with control infants (P

<

.005), whereas the control infants had significantly higher CPEN mean titers compared with study infants (P

<

.001).

The measles-specific 1gM response of the 63 study infants (52.1% ofthe 121 initially HI negative infants) who had no detectable antibody by any of the three assays prior to revaccination were com-pared with the response of 50 randomly chosen control infants who were also seronegative by these three assays prior to primary vaccination (Table 2).

TABLE 1. Antibody Test R Infants 3 Weeks Following Vaccination*

esults of Study Revaccination

and Control or Primary

Antibody Study Infants

Test

Control Infants P Value

HI 29.53 (121) CPEN 156.90 (120)

ELISA 0.456 (102)

22.69 (127) 276.65 (126) 0.266 (107) <.005 <.001 <.001

* Results are geometric mean titers by hemagglutinatiori

inhibition (HI) and cytopathic effect neutralization

(CPEN)

tests and mean optical density values by en-zyme-linked immunoassay (ELISA) of initially HI-neg-ative infants. Numbers in parentheses are numbers of blood specimens tested. Probability was determined by

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TABLE 2. Presence of Detectable Measles-Specific 1gM Antibody 3 Weeks Following Revaccination or

Pri-mary Vaccination*

50

40

.- 30

E 20

(3<

10

300

Day 0 3 Weeks 8 Months

Measles-Specific 1gM Titer 14 P Value

Subject Infants Control Infants

(n=63) (n=50)

No. 14 37 <.001

%

22.2 74.0

* Infants were seronegative for all three antibodies by

hemagglutination inhibition, cytopathic effect neutrali-zation, and enzyme-linked immunoassay tests prior to revaccination (study infants) or primary vaccination

(control infants). Numbers in parentheses are the

num-hers of blood specimens tested. Probability was tested by

x2test with Yates correction.

Subjects (Revaccination)

--- -Controls (Primary

vaccination)

Day 0 3 Weeks 8 Months

Fig 2. Geometric mean titers (GMT) of hemagglutina-tion inhibition (HI) and cytopathic effect neutralization

(CPEN) antibodies and mean enzyme-linked

immunoas-say (ELISA) optical density values. Results are shown

for infants whose first blood specimens were negative for HI antibodies.

Fourteen (22.2%) of these study infants had detect-able measles-specific 1gM antibody as compared with 37 (74.0%) of the control infants (P

<

.001). In graphic form (Fig 2), the mean antibody levels are shown by all three tests for the

S,, S2,

and S3 sera for all initially HI negative infants. By 8 months after revaccination (study infants) or pri-mary vaccination (control infants), the 121 initially HI negative study infants had statistically signifi-cantly lower antibody levels than control infants by all three assays (P

<

.001). These study infants

were also less likely than control infants to have detectable HI antibody (1:8) or detectable ELISA antibody (0.056) (P

<

.001) (Table 3). However, the proportion of study infants with detectable neutralizing antibody was not significantly differ-ent from control infants.

Of the 129 study infants having an initial HI titer

1:8, all had detectable HI, CPEN, and ELISA antibody at 3 weeks and 8 months after revaccina-tion. The mean HI and CPEN antibody titers were not significantly different between these 129 study infants and the control infants 8 months after revaccination (study infants) or primary vaccina-tion (control infants), although the mean ELISA antibody titer was significantly lower at this time in these study infants (mean = 0.389) compared with the control infants (mean = 0.478) (P

<

.001).

The percentage of all infants with detectable measles antibody by the three assays 8 months after revaccination (study infants) or primary vaccina-tion (control infants) is shown in Table 4. Of all infants receiving measles vaccine prior to 10 months of age in this study, 76.4% had detectable HI antibodies, 92.3% had detectable ELISA anti-bodies and 98.4% had detectable CPEN antibodies. There were significant differences in the prevalence of HI and ELISA antibodies, but there were no significant differences in prevalence of neutralizing antibody or in the percentage with any detectable antibody.

Control infants were significantly more likely to experience fever within 3 weeks of vaccination than study infants (37.2% v 17.9%) (P

<

.001). Although control infants were more likely to have a rash than study infants (9.3% v 4.3%), this difference was not

statistically significant (P = .09).

DISCUSSION

The results of the present study confirm the findings of previous studies3’4’7 that some infants who are vaccinated with measles vaccine before 10 months of age have an altered immune response to this antigen. Not only are such infants likely to have a quantitatively poorer response on primary vaccination than older children, they also may have an altered response on revaccination. In the present study, about one quarter of such infants had no detectable HI antibody 8 months after revaccina-tion compared with only 2% of control infants. Antibody titers of these study infants 8 months after revaccination were more likely to be lower than those ofcontrol infants. The younger the child at the time of primary vaccination, the greater the likelihood of this altered immune response.

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TABLE 3. Comparison of Initially Hemagglutinat With Detectable Antibody Titers at 8 Months Follo

or Primary Vaccination (Control Infants)*

ion Inhibition Seronegative Infants wing Revaccination (Study Infants)

Assay Study Infants

(%)

Control Infants P Value

(%)

HI 1:8 52.1 (121)

CPEN 1:4 96.7 (120)

ELISA 0.056 84.4 (109)

HI 1:8 or CPEN 1:4 96.7 (121)

or ELISA 0.056

97.6 (127) <.001 99.2 (127) .335 99.2 (118) <.001 99.2 (127) .340

*Abbreviations used are: HI, hemagglutination inhibition; CPEN, cytopathic effect neu-tralization; ELISA, enzyme-linked immunoassay. Numbers of blood specimens tested are given in parentheses. Probability was tested by Fisher exact two-tailed test.

TABLE 4. Comparison of All In Following Revaccination (Study In

fants With Detectable Antibody Tite fants) or Primary Vaccination (Contr

rs at 8 Months ol Infants)* Assay Study Infants Control Infants P Value HI 1:8

CPEN 1:4

ELISA 0.056

HI 1:8 or CPEN 1:4 or ELISA 0.056

76.4 (254) 97.7 (129) 98.4 (253) 99.2 (129)

92.3 (234) 99.2 (118)

98.4 (253) 99.2 (129)

<.001 .903

<.008

.903

* Abbreviations used are; HI, hemagglutination inhibition; CPEN, cytopathic effect

neu-tralization; ELISA, enzyme-linked immunoassay. Numbers of blood specimens tested are given in parentheses. Probability was tested by Fisher exact two-tailed test.

assays of a similar group of subjects in San Anto-nio.7 In that study, the percentage of ELISA sero-negative children was the same in both subjects and controls, whereas in the present study, study

in-fants were significantly less likely to have detecta-ble ELISA antibody than control infants. This might be explained by the younger mean age of

infants receiving the first dose of measles vaccine in the present study (mean age = 6.8 months)

as

compared with the San Antonio study (mean age = 7.8 months). The children who failed to seroconvert in the San Antonio study were all less than 270 days of age; the sample was too small to attain

statistical

significance.

Also, the ELISA test used

in the present study only measured IgG and did not measure significant amounts of 1gM or IgA. This

probably explains the shape of the ELISA curve for control infants in Fig 2, ie, the S3 value being higher than the S2 value.

The finding that nine (7%) of the control infants had detectable measles neutralizing antibody on the day of their primary immunization at 15 months of age could raise questions about the specificity of the CPEN test. Of the eight control infants in the

present

study with neutralizing antibody detectable on the day of vaccination and adequate volume of blood for 1gM testing, four had initial levels of neutralizing antibody <1:10; they had positive

mea-sles-specific

1gM responses 3 weeks after immuni-zation, which suggests that these low levels of

an-tibody were probably of maternal origin. The

re-maining four control infants had initial neutralizing

titers

of

>1:20 and did not have a measurable

measles-specific

1gM response. These controls may have had prior undiagnosed (or modified) measles disease or received measles vaccine that had not

been recorded.

The critical question is whether children with an altered measles immune response following early

measles

vaccination

and

later

revaccination

are

protected from measles disease. In the present

study, few initially seronegative study infants made

measles-specific

1gM, and most had an initial HI

response greater than that of control infants, sug-gesting that the immune system was primed and would respond rapidly to infection. Also, almost all

study

infants

had some

form

of measles

antibody

8

months

after

revaccination.

Even

more

impor-tantly, 98%

of

all study infants had measurable neutralizing antibody present 8 months after revac-cination. This type of antibody is thought to cor-relate best with protection.9 Thus, these results,

based

on the largest

number

ofchildren

yet reported

and assessing the immune response more fully than

in previous

studies,

suggest

that

almost

all measles

revaccinees

initially vaccinated at less than 10

months of age are protected.

The only relevant data on clincial protection

following revaccination of infants initially receiving

measles vaccine prior to a year of age were obtained

during

a measles

outbreak

in Michigan

in

1975.

(6)

months of age and revaccinated after 12 months of age were significantly better protected than persons vaccinated before 12 months of age but not revac-cinated (P

<

.001); however, the number of persons

initially vaccinated at 6 to 8 months of age in the study was too small for meaningful comparison.10

Data from the present study support the current Immunization Practices Advisory Committee of the US Public Health Service and American Academy of Pediatrics recommendations that, when there is a substantial risk of acquiring measles, infants as

young as 6 months of age may be vaccinated because

infants are much more likely to have severe com-plications from measles such as pneumonia. They should then be revaccinated at 15 months of age

to ensure protection. Further serologic studies are unlikely to provide meaningful new information. Only more data on clinical protection can corn-pletely resolve the issue.

ACKNOWLEDGMENTS

We thank Mr Herb Bostrom ofthe Wisconsin Division

of Health for administrative support. We also thank Mrs Margaret Chamberlain, RN, and Ms Janet Horton, RN, for enrolling the study participants, drawing bloods, and collecting the data.

REFERENCES

1. Immunization Practices Advisory Committee: Measles

pre-vention. MMWR 1982;31:217-231

2. Report of the Committee on Infectious Diseases: The 1982 Red Book, ed 19. Evanston, IL, American Academy of Pe-diatrics, 1982, p 136

3. Wilkins J, Wehrle PF: Additional evidence against measles

vaccine administration to infants less than 12 months of age: Altered immune response following active/passive im-munization. J Pediatr 1979;94:865-869

4. Linnemann CC Jr, Dine MS, Roselle GA, et al: Measles

immunity after revaccination: Results in children vacci-nated before 10 months of age. Pediatrics 1982;69:332-335 5. Hierholzer JC, Suggs MT, Hall EC: Standardized viral

hem-agglutination and hemagglutination-inhibition tests: II. De-scription and statistical evaluation. AppI Microbial 1969; 18:824-833

6. Albrecht P, Herrmann K, Burns GR: Role of virus strain in conventional and enhanced measles plaque neutralization

test. J Virol Methods 1981;3:251-260

7. Murphy MD, Brunell PA, Lievens AW, et al: Effect of early immunization on antibody response to reimmunization with measles vaccine as demonstrated by enzyme-linked immu-nosorbent assay (ELISA). Pediatrics 1984;74:90-93

8. Vesikari T, Vaheri A: Rubella: A method for rapid diagnosis

ofa recent infection by demonstration ofthe 1gM antibodies.

Br Med J 1968;1:221-223

9. Stokes J Jr, Reilly CM, Buynak EB, et al: Immunologic studies of measles. Am J Hyg 1961;74:293-303

10. Shasby DM, Shope TC, Downs H, et al: Epidemic measles

in a highly vaccinated population. N Engi J Med 1977;296: 585-589

NOT A BAD IDEA

All medical careers would begin with a position as orderly, which would be transformed into the first stage of a possible apprenticeship for physicians. After a given number of years, successful candidates could leave for a few years of medical school (2 years seems sufficient background for most practition-ers . . .) and then return to the hospital for advanced apprenticeship training of

the sort now given in internship and residency programs. . . . Advanced

special-ties could continue to be taught as they now are-through further on-the-job training; only medical researchers would be involved in lengthy schooling.

Randall Collins

(7)

1986;77;471

Pediatrics

Brunell

Sirotkin, Dan Hopfensperger, Ruth Schuh, Paul Albrecht, Alan W. Lievens and Philip A.

Harrison C. Stetler, Walter A. Orenstein, Roger H. Bernier, Kenneth L. Herrmann, Barry

Months of Age

Impact of Revaccinating Children Who Initially Received Measles Vaccine Before 10

Services

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