Singapore’s vaccination programme successful; kids, teens safe from measles, rubella

Antibodies against common vaccine-preventable diseases, such as measles, rubella, diphtheria, and tetanus, are highly prevalent among Singaporean children and adolescents, according to a new study.

These findings suggest that massive vaccination campaigns in the country are effective, and that continuing such efforts would be fruitful.

“The high seroprevalence levels corresponded with vaccination rates of more than 96 percent for these four diseases, as well as the low disease incidence rates reported in Singapore,” the researchers said, adding that seroprevalence was also better than the expected herd immunity thresholds. People who had not been immunized, therefore, also enjoyed strong protection against outbreaks of these diseases.

A total of 1,200 children and adolescents were enrolled from the 2018 National Paediatric Seroprevalence Survey. The prevalence rates of antibodies against measles and rubella were estimated at 98.2 percent and 94.8 percent, respectively. [Int J Infect Dis 2020;92:234-240]

For both diseases, seropositivity increased with age, jumping from 95.3 percent and 91.0 percent, respectively, in kids aged 1–6 years, to 99.8 percent and 96.8 percent in teens between the ages of 13 and 17 years. No such discrepancies were detected between ethnic groups.

Diphtheria and tetanus were likewise well-covered. At least 97 percent of survey participants had at least a basic protection against diphtheria, while this was true for tetanus in 89.3 percent. Older participants also saw significantly stronger immunization against tetanus, with seropositivity rates increasing from 87.8 percent in early childhood to 96.0 percent in adolescence.

Importantly, there seemed to be a strong interaction between vaccination status and seroprevalence. For instance, only about half of the participants who had been vaccinated for measles were immune to the disease, while 98.9 percent and 99.8 percent of those who received a single or the full dose of the vaccine showed immunity.

“Concordance between vaccination status and seroprevalence of antibodies/antitoxins was observed across all three age groups for measles, rubella, diphtheria, and tetanus, that is, the unvaccinated subjects were less protected than the vaccinated ones,” the researchers explained.

“However, this distinction became less apparent in the older age groups, which suggested natural acquisition of immunity in unvaccinated children over time,” they added.

On the other hand, less than half of the participants showed immunity against the hepatitis B virus, and seropositivity decreased with age, contrary to the above trends. Antibodies were present in 74.0 percent of children aged 1–6 years, while only 24.0 percent of teens aged 13–17 years showed the same.

Concordance between vaccination and immunity statuses was weaker in the case of hepatitis B. While almost all participants had records of receiving the vaccine, seroprevalence remained relatively low, even among those who had been given the full course. This could be due to the established waning over time of the antibodies against hepatitis B. Nevertheless, immunity against the disease remains even at lower antibody levels.

“Although the seroprevalence of antihepatitis B was relatively low, the high vaccination uptake and low disease incidence rates suggested that a high percentage of the paediatric population remained protected against hepatitis B,” the researchers said.

“Our results also highlighted the effectiveness of the National Childhood Immunization Programme (NCIP). Continual efforts in ensuring high vaccination coverage for NCIP should be sustained,” they added.