Immune response of infants in tropics to injectable polio vaccine

Immunologic memory induced at birth by immunization with inactivated polio vaccine in a reduced schedule

One hundred forty-one healthy newborns were immunized 24 hours after birth with one dose of inactivated polio vaccine (IPV) of enhanced potency. Following the administration of a second vaccine dose six months later, a considerable proportion of babies responded with neutralizing antibody (NA) to the three poliovirus types. The very rapid occurrence and high antibody titer were indicative of an anamnestic response. Twenty-one infants who still had NA less than 1:4 to one-more poliovirus types after the second vaccine dose responded with very high NA values 7-10 days after a supplementary dose of IPV. It appears that IPV of enhanced potency administered at birth is apt to induce immunologic memory, which should provide the basis for protection against paralytic poliomyelitis in case of exposure to wild poliovirus later in life.

[Relative immunity to poliomyelitis in children from 0 to 10, after the 4th National Polio Vaccination Day with trivalent oral type Sabin vaccination, in the area of greater São Paulo, SP (Brazil), 1982]

Efetuou-se um levantamento soro-epidemiológico, abrangendo 898 crianças, para a verificação da imunidade aos poliovírus 1, 2 e 3 por meio da determinação dos títulos de anticorpos neutralizantes. De 522 crianças, ou seja, de 58,1% da população estudada, foi possível a obtenção de informações referentes à situação vacinal a partir de anotações existentes nas próprias Cadernetas de Vacinação. Neste último sub-grupo foi estudado o estado imunitário em relação ao número de doses de vacina oral tipo Sabin recebidas. Os resultados mostraram alta proporção de imunes para os três tipos de poliovírus entre as crianças estudadas, porém também revelaram a existência de lacuna imunitária nos menores de um ano, especialmente no primeiro semestre de vida. Não foram observadas diferenças importantes na proporção de imunes segundo o sorotipo considerado. Salientou-se a necessidade de um alerta constante e permanente em relação à ocorrência de possíveis surtos epidêmicos em segmentos mais vulneráveis da população, particularmente entre crianças menores de 1 ano.

Efficacy of inactivated poliovirus vaccine in India

The immunogenic efficacy of inactivated (Salk) poliovirus vaccine (IPV) was evaluated in infants in India, in view of the high frequency of vaccine failure after immunization with oral (Sabin) poliovirus vaccine (OPV). A total of 150 infants, aged 6-45 weeks, were given 3 doses of IPV, with intervals of 4 or 8 weeks between doses. The effect on the antibody response of child's age, presence of maternal antibody before immunization, and interval between doses was assessed. The overall seroconversion rates to poliovirus types 1, 2, and 3 were 99%, 89%, and 91%, respectively. Seroconversion rates to types 2 and 3, and antibody titres to types 1 and 2, were higher (i) in infants given vaccine doses at 8-week intervals and (ii) in those without detectable maternal antibody. The seroconversion rates in infants without maternal antibody, who were given IPV at 8-week intervals, were 100%, 100%, and 96.2% to poliovirus types 1, 2, and 3, respectively. Thus the immunogenic efficacy of IPV was found to be satisfactory.