Early immunization of neonates with trivalentoral poliovirus vaccine*L.Y. Weckx,1 B.J. Schmidt,2 A.A. Herrmann,3 C.H. Miyasaki,4 & N.F. Novo5

Described is the evaluation in Brazil of the immune response of early immunization with trivalent oralpoliovirus vaccine (TOPV). A total of 85 normal neonates from Sao Paulo were assigned one of the fol-lowing immunization schedules: group A - one dose of TOPV at birth and subsequent doses at 2, 4,and 9 months of age; or group B - one dose of TOPV at 2, 4 and 6 months of age. Blood sampleswere collected sequentially from the mother at delivery, from the umbilical cord, and from the child at 2,4, 6, 9 and 12 months of age for assay of poliovirus neutralizing antibodies. Administration of TOPV atbirth, in addition to establishing immunity against poliomyelitis at an earlier stage, produced a superiorimmune response to poliovirus type 3. At the end of the first year, the proportion of susceptible indivi-duals was 3.7% in group A and 25.9% in group B. When immunization against poliomyelitis is started atbirth, excellent seroconversion rates are obtained from the third dose onward.

IntroductionImmunization of neonates with oral poliovirus vacci-ne (OPV) was studied extensively in the 1950s and1960s (1-10). Recently, this possibility has been re-evaluated, because in developing countries, wherepoliomyelitis is not yet under control, early vaccina-tion would permit immunization at a time when thereis little interference from intestinal organisms andensure the administration of at least one dose whilethe child is still under medical care. In Sao Paulo,Brazil, more than 90% of deliveries occur in hospi-tals. Also, the occurrence in very young childrena ofpoliomyelitis that is associated with an immunity gap(11) would be prevented by earlier establishment ofimmunity against the disease. Recently, studies car-ried out in China (12) and in India (13) have reportedexcellent rates of seroconversion after early adminis-tration of poliovirus vaccine, with higher antibodytitres during the first months of life (12,14).

On the basis of these data WHO now recom-mends a supplementary dose of polio vaccine at

* From Escola Paulista de Medicina, Sao Paulo, Brazil.

Associate Professor, Division of Puericulture and SocialPaediatrics, and Division of Immunization, Secretary of Health,State of Sao Paulo, Brazil. Requests for reprints should be sentto Dr Weckx at: Escola Paulista de Medicina, Departamento dePediatria, Rua Botucatu, 740, 04023-Sao Paulo- SP, Brazil.2 Professor, Division of Puericulture and Social Paediatrics.3Assistant Professor, Division of Puericulture and SocialPaediatrics.4Associate Professor, Division of Neonatology.5Associate Professor, Division of Biostatistics.a Neves, W.E. [Some aspects of poliomyelitis in the first 6-months of life. A study of 241 cases]. Doctoral thesis, Faculty ofMedicine, University of Sao Paulo, 1972 (in Portuguese).Reprint No. 5251

birth, in addition to the three doses for primaryimmunization (15,16). We therefore carried out astudy to assess the immunological response to earlypoliomyelitis vaccination of neonates in Sao Paulo.

Materials and methodsThe protocol was approved by the Committee ofEthical Control of Clinical Research, Escola Paulistade Medicina, Sao Paulo.

Study population

A total of 85 children from Sao Paulo were evaluatedfrom March 1986 to September 1988. The childrensatisfied the following criteria: they were normalfull-term newborn infants, had a birth weight of over2500g, and a 5-minutes Apgar score of >7. In addi-tion, their mothers had normal pregnancies, withoutinfectious episodes, and amniorrhexis less than 12hours before delivery. After obtaining the writtenconsent of one of the parents, the neonates were assi-gned at random to one of two groups (A and B), eachof which received different poliomyelitis immuniza-tion schedules. All children were followed up in thenursery and afterwards at monthly visits throughoutthe first year of life. Those who received an extradose of vaccine as a result of immunization campai-gns were excluded from the study. Of the 85 neo-nates at the beginning of the study, only 54 (27 ineach group) followed the protocol until the end.

Immunization schedules

Trivalent oral poliovirus vaccine (TOPV;SmithKline), which was distributed by the Ministry

Bulletin of the World Health Organization, 70 (1): 85-91 (1992) © World Health Organization 1992 85

L.Y. Weckx et al.

of Health, was used for both study groups; however,because the composition of the vaccine was modifiedduring the study period, group B children received ahigher concentration of vaccine to poliovirus type 3.The schedules and composition of vaccine used withthe two study groups are shown below.- Group A: TOPV was given at birth (second day

of life) and subsequently at 2, 4, and 9 months ofage. Composition of vaccine: poliovirus type 1(PI) = 1 million TCID50; type 2 (P2) = 100 000TCID50; and type 3 (P = 300 000 TCID50.

- Group B: TOPV was given according to the offi-cial schedule established in Brazil, i.e., at 2, 4and 6 months of age. Composition of vaccine:P1 = 1 million TCID50; P2 = 100 000 TCID50; andP3 = 500 000 TCID50.

Laboratory tests

In each case blood samples were collected from themother at delivery, from the umbilical cord, andfrom the child, by venepuncture, at 2, 4, 6, 9 and 12months of age. Sera, which were obtained by centri-fugation of the blood samples, were stored at -20 °Cuntil being analysed. The levels of types 1, 2 and 3poliovirus antibodies were assayed by the neutraliza-tion technique (17) at dilutions of between 1:5 and1:10 240.

Evaluation parameters

Individuals whose poliovirus neutralizing antibodytitres were .1:5 were considered to be seropositive(11, 18, 19). Seroconversion was taken to be de-velopment of poliovirus neutralizing antibodies inpreviously seronegative individuals or at least a four-fold increase in the expected titre caused by a reduc-tion in transplacental antibodies. A maternal anti-body half-life of 30 days was assumed for thispurpose (16).

Statistical analysisBecause of our sample characteristics, the followingnonparametric methods were used in the statisticalanalysis of the results: Wilcoxon's, Friedman's andCochran's G tests; the level of significance was 0.05(5%). For calculation of the geometric mean anti-body titres (GMT), titres <1:5 were taken to be equalto 1:2.5 and those >1:10 240 to be 1:20 480 (20).

ResultsWith the exception of one child, poliovirus neutrali-zing antibodies were present in all the children atbirth; the antibody levels were lower in the umbilical

cord (GMT: P, = 109.49; P2 = 71.77; and P3 =46.88) than in maternal blood (GMT: P1 = 130.03;P2 = 100.45; and P3 = 73.87). The difference was sig-nificant for P2.

Sequential determination of poliovirus anti-bodies in a given child throughout the first year oflife permits evaluation of the serological response tothe vaccine. The results obtained were analysed forantibody level, seropositivity, susceptibility and sero-conversion.

Antibody level

For group A children (who received TOPV at birth)a slight decrease in the antibody titres to P1 and P3occurred between birth and the second month of life,but increased thereafter (Fig. 1). In general therewas a good serological response to this vaccinationschedule, leading at the end of the first year to highantibody titres against the three polioviruses.

For group B children (who were immunized firstat the age of 2 months) the antibody levels for thethree polioviruses decreased significantly until thesecond month. This was due to the natural loss ofmaternal antibodies present at birth. The reduction inantibodies to P3 was more pronounced, with theincrease in titres occurring only from the fourthmonth onward. At the end of the first year the meantitres for P2 (557.22) and P1 (153.03) were consider-ably greater than the mean for P3 (40.02).

SeropositivityIn group A the percentage seropositivity (titre >1:5)for P1 and P2 was rather high and constant during thefirst year of life. The seropositivity for P3 decreasedin the second month, but recovered subsequently,and by the end of the primary immunization sched-ule, the protection rates against the three polioviruseswere excellent (Fig. 2) (Pi=100%, P2=100%,and P3=96.3%).

In group B, although the seropositivity for P,and P2 remained high, there was a significant decrea-se in that for P3 until the fourth month (minimumseropositivity, 51.9%). At the end of the first year,while high seropositivity rates were obtained for Piand P2, only 74.1% of the children were protectedagainst poliovirus P3.

SusceptibilityIndividuals who are susceptible to one, two, or threetypes of poliovirus were classifled as singly, doublyor triply susceptible, respectively. Almost all suscep-tible individuals in group A were singly susceptible,while in group B there were a considerable number

86WHO Bulletin OMS. Vol 70 199286

Early immunization of neonates with oral poliovirus vaccine

Fig. 1. Geometric mean titres (reciprocal) for poliovirus neutralizing antibodies in group A and group B children;P1 = poliovirus type 1; P2 = poliovirus type 2; P3 = poliovirus type 3.

Group A Group B5

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Age (months)

Antibody titres (reciprocal of GMT)

9

Cord 2 months 4 months 6 months 9 months 12 months

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Age (months)

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Cord 2 months 4 months 6 months 9 months 12 monthsP1 86.45 63.13 145.72 180.08 123.06 205.63 P1 138.69 33.66 102.17 152.44 152.73 153.03P2 65.46 193.64 840.26 805.20 457.74 532.67 P2 78.69 28.66 495.34 789.74 637.53 557.22P3 41.06 16.75 84.99 165.96 93.96 97.67 P3 53.54 13.88 9.67 31.02 39.67 40.02

Fig. 2. Percentage of seropositive individuals (antibody titre >1:5) for poliovirus in group A and group B; P1 = polio-virus type 1; P2 = poliovirus type 2; P3 = poliovirus type 3.

Group A Group B

100 -N -N011 -1

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..... ~~~~~~~~~..... .................................- P1-- P2

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87

L.Y. Weckx et al.

of doubly susceptible individuals, in addition to a

higher overall proportion of susceptible individuals.In group A, the proportion of susceptibles aged 2-6months was particularly low. At the end of the twoschedules the proportion of susceptible individuals ingroup A was 3.7%, while in group B it was 25.9%(Fig. 3).

Seroconversion

Seroconversion, an important parameter in evalua-ting the active response to a vaccine, was determinedby assaying the antibody levels in both groups twomonths after each dose of vaccine had been adminis-tered (Fig. 4).

For children in group A, seroconversion increa-sed progressively with each successive dose. Afterthree doses (including dose zero given at birth, therate of seroconversion for the three polioviruses was

high (PI = 92.6%, P2 = 96.3%, P3 = 92.6%), andclose to that obtained after four doses (dose 3) (P1 =

100%, P2 = 100%, P3 = 96.3%).High rates of seroconversion for P1 (96.3%) and

P2 (100%) were obtained for children in group B;however, only 74.1% of these children had sero-

converted to the P3 vaccine virus by the end of theschedule.

DiscussionOne of the problems associated with early immuni-zation with TOPV is the possible interference ofmaternal antibodies with the response to the adminis-tered vaccine (1-6, 12). In the present study, passive-ly transferred maternal antibodies were present in allbut one neonate and did not seem to have influencedthe final outcome, since almost all children in group

A seroconverted. Dong et al. have shown that theseroconversion is delayed when high levels of mater-nal antibodies are present at birth (12); in contrast,we found this outcome only for P1. Because of thesmall number of patients in our study, the evaluationfor other poliovirus types was difficult. The highgastric acidity during the first 24 hours of life(21,22) and the presence of ingested amniotic fluid(23) could theoretically interfere with vaccines givenimmediately after birth; the children were thereforevaccinated on their second day of life. Also, the chil-dren in our study were routinely breast-fed.

Administration of a supplementary dose ofTOPV at birth led to a higher level of polio antibo-dies during the first months of life (Fig. 1), with a

greater seropositivity (Fig. 2), and consequently to a

decrease in the proportion of susceptible individualsover this period (Fig. 3). Use of a supplementarydose at birth led also to increased protection at theend of the primary immunization schedule: only

Fig. 3. Percentage of susceptible individuals (antibody titre <1:5) for poliovirus in group A and group B: single =

susceptible to one poliovirus type; double = susceptible to two poliovirus types; total = all susceptibles.

Group A Group B

50

0 401-

30

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10

0 2 4 6Age (months)

9 12 0 2 4 6Age (months)

0

9 12

WHO Bulletin OMS. Vol 70 1992

- Double-- Single. Total

- - ~

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Il N. 1 4.'

88

Early immunization of neonates with oral poliovirus vaccine

Fig. 4. Percentage seroconversion to poliovirus types after each dose of vaccine. Seroconversion was defined as thedevelopment of antibodies in formerly seronegative individuals or a .4-fold increase in the level of a type-specific antibody.Assays were performed 2 months after administration of each dose of vaccine. P1 = poliovirus type 1; P2 = poliovirus type2; P3 = poliovirus type 3.

Group A

100

80

Group B

Dose 0 Dose 1 Dose 2 Dose 3 Dose 1 Dose 2 Dose 3(birth) (2 months) (4 months) (9 months) (2 months) (4 months) (6 months)

E P1i P2 P3

3.7% of susceptible individuals were in group A,compared with 25.9% in group B, whose schedulebegan in the second month of life. How can theimproved serological response in children whoreceive TOPV at birth be explained? Why were thesame results not observed in 2-month-old childrenwho had already developed immunological mechan-isms, were subject to little interference from maternalantibodies, and who had received a more concen-trated vaccine?

In India, John obtained excellent rates of sero-conversion in children who received their first doseof poliovirus vaccine during the first week of life,the rates being slightly higher than those resultingfrom administration of the vaccine at 5 or 6 weeks ofage (13). In Brazil, Neves et al. have reported betterrates of seroconversion when administration ofTOPV is started in the first rather than in the third

month of life (24). It should be noted that these twostudies were performed in tropical countries, wherethe efficacy of the routinely administered oral polio-vaccine is lower than that in countries with tempera-te climates (25, 26). Several factors play a role inaccounting for these differences: potency is reducedin tropical countries because of deficiencies in thestorage of the vaccine (27); there could be diffe-rences in inhibitory factors in the digestive tract thathave an effect on the implantation and replication ofthe vaccine virus (28); and the interference by otherenteroviruses in small children in tropical countriesmay reduce the immune response (29-32). The inci-dence of enterovirus infections among neonates inBrazil (33) and elsewhere (34) is significantlylower than that among older children, and may ac-count for the better seroconversion rates observed inyounger children. Our results indicate that there is

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L.Y. Weckx et al.

an improved serological response to TOPV whenthe schedule is started early, during the neonatal per-iod, particularly as far as poliovirus type 3 is con-cerned.

During the outbreak of poliomyelitis in north-east Brazil in 1986, most cases were due to polio-virus type 3. Epidemiological investigations haverevealed that the TOPV used to immunize the chil-dren has a low efficacy, particularly in terms of theP3 component. Higher seroconversion rates wereobtained by doubling the P3 level (35), and this ledthe Brazilian Ministry of Health to modify the com-position of the vaccine used, increasing the P3 levelfrom 300 000 TCID50 per dose to 500 000 TCID50per dose.

The children in group B in our study who re-ceived their first dose of TOPV in their secondmonth of life, were immunized from the beginningwith a vaccine that had the higher P3 level. Even so,the rate of seroconversion to P3 was lower than thatof children who received their first dose at birthusing vaccine with a P3 level of 300 000 TCID50 perdose. This indicates that immunization of neonateswith TOPV may be a much more relevant factorthan use of a higher vaccine concentration.

With the official schedule, beginning in thesecond month of life, primary immunization withthree doses of TOPV resulted in about 25% of thechildren remaining incompletely immunized, andsusceptible to poliovirus type 3. In the case of expo-sure to wild poliovirus this proportion of the popula-tion can be considered to be at risk. In contrast, withearly immunization, better protection can beachieved and the risk may diminish considerably.

When a supplementary dose of TOPV is givenat birth (zero dose), excellent rates of seroconversionfor the three poliovirus types are produced from thethird dose onward, and after the fourth dose, theseroconversion rates are still slightly higher (Fig. 4).

No difficulty was experienced in administeringthe TOPV to neonates. The schedule is feasibleoperationally and requires no specialized technicalknowledge or additional equipment. In view of theresults obtained, we propose that immunizationagainst poliomyelitis be initiated early in the neona-tal period; every newborn can receive the first doseof polio vaccine before being discharged from hospi-tal. This measure together with other efforts toimprove vaccination will contribute considerably tothe control of poliomyelitis.

AcknowledgementsWe are indebted to the Institut Merieux, for carrying outthe laboratory tests; the Centre International de l'Enfance,

for valuable suggestions; and to CNPq (BrazilianResearch Council), for financial support.

ResumeVaccination precoce des nouveau-n6s parle vaccin antipoliomyelitique buccaltrivalentLa vaccination des nouveau-nes contre la polio-myelite offre certains avantages; par exemple,l'enfant recoit la premiere dose de vaccin lorsqu'ilest encore a I'hopital, a un age ou il y a peud'interference avec les germes enteriques et, sur-tout, cela permet d'assurer une protection precocecontre la maladie.

Nous avons effectu6 une 6tude visant a quan-tifier la r6ponse immunitaire a une vaccinationantipoliomyelitique pr6coce avec un vaccin buccaltrivalent (VPOT) a Sao Paulo, au Bresil. Au total,85 nouveau-nes normaux ont forme la populationd'6tude, qui a 6te divisee au hasard en deuxgroupes soumis a differents calendriers vaccinaux:groupe A - une dose de VPOT a la naissance puisa 2, 4 et 9 mois; groupe B - une dose de VPOT a2, 4 et 6 mois. Dans chaque cas, on a effectu6des pr6levements sanguins au moment de l'accou-chement chez la mere et au cordon ombilical, puischez l'enfant a 2, 4, 6, 9 et 12 mois. On a ainsiobtenu une evaluation s6quentielle de l'immunit6antipoliomyelitique au cours de la premiere annee.On a titr6 les anticorps des trois souches de polio-virus par neutralisation.

L'administration d'une dose suppl6mentaire deVPOT a la naissance, outre qu'elle etablit l'immu-nite antipoliomyelitique a un age plus precoce,produit egalement une meilleure reponse immuni-taire contre le P3. A la fin de la premiere annee, laproportion de sujets sensibles etait de 3,7% dansle groupe A et de 25,9% dans le groupe B. Lafaible incidence des infections enterovirales chezle nouveau-n6 a peut-etre contribu6 a cettemeilleure r6ponse immunitaire. Lorsqu'on com-mence la vaccination antipoliomyelitique des lanaissance, on obtient d'excellents taux de sero-conversion a partir de la deuxieme dose c'est-a-dire a 4 mois.

Notre calendrier vaccinal est tout a fait appli-cable et chaque enfant a requ sa premiere dosede vaccin avant sa sortie de l'h6pital. Cette faconde proceder devrait se g6neraliser, en particulierdans les pays ou cette maladie s6vit encore.

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Early immunization of neonates with oral poliovirus vaccine

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27. Sokhey, J. et al. Stability of oral polio vaccine atdifferent temperatures. Vaccine, 6: 12-13 (1988).

28. Domok, I. et al. Factors affecting the efficacy of livepoliovirus vaccine in warm climates. Bulletin of theWorld Health Organization, 51: 33-47 (1974).

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