[TOPick] Pneumococcal Disease | Children Vaccinated with Previous Generation Pneumococcal Vaccine Still Susceptible Infection; Vaccination Must Target Serotype 3; Early Reinforcement of Protection Reduces Infection Risk | Paediatric Specialist Dr. Chan Yan-wing | 2024-06-07

Over the past year, children who were vaccinated against pneumococcal disease in infancy have unfortunately contracted serotype 3 pneumococcal pneumonia, leading to severe complications and even death. The underlying reason may involve traditional vaccines not effectively preventing serotype 3 pneumococcal infections currently prevalent in Hong Kong. As parents, it is essential to be vigilant, discuss with your doctor, and consider whether a booster dose of the latest 15-valent vaccine targeting serotype 3 is needed for your children to achieve maximum protection.

Besides the elderly, children are also targets of pneumococcal attacks. This bacterium, commonly found in the nose and throat, can spread through droplets, contact with patients, or touching objects contaminated with the bacteria. It can lead to complications such as middle ear infections, pneumonia, meningitis, bacteremia, and sepsis, with potentially severe consequences.

Although children in the Hong Kong Childhood Immunisation Programme receive two doses at two and four months old, followed by a third dose at 12 months, the extent to which the vaccine can provide protection against serotype 3, which is most prevalent in Hong Kong, will be a key consideration.

Serotype 3. Most common local serotype.

Previously, pneumococcal vaccines available included the 13-valent pneumococcal conjugate vaccine and the 23-valent pneumococcal polysaccharide vaccine. Last year, 15-valent conjugate and 20-valent conjugate vaccines were introduced, with the latter only for adult use. Some parents may wonder if their children need to receive the 15-valent pneumococcal vaccine if they have already had the 13-valent pneumococcal vaccine.

Regarding this issue, the first thing to consider is whether the serotypes covered by the vaccine can target the prevalent serotypes of pneumococcal disease in Hong Kong. The Scientific Committee on Vaccines Preventable Diseases of the Centre for Health Protection points out that Streptococcus pneumoniae serotype 3 is the most common serotype causing invasive pneumococcal disease in children in Hong Kong, accounting for as high as 70% of all cases from 2015 to 2019. The World Health Organization recommends that when considering pneumococcal vaccination, local prevalent serotypes should be taken into account. Using Hong Kong as an example, whether the vaccine can target serotype 3 is a crucial factor.

Serotype 3 is characterised by high severity, high resistance to treatment and a high mortality rate; the bacterial cells of this serotype are larger than those of other serotypes, requiring a greater quantity of antibodies to combat them.Data further indicates that the mortality rate for infections caused by this serotype is as high as 47%, with children under five and adults over 50 being particularly at high risk.

Children's booster jabs for targeted protection

When comparing the pneumococcal vaccines currently available in Hong Kong, studies show that in adults aged 50 and over, the 15-valent vaccine induces a 60% higher immunogenicity than the 13-valent vaccine; in infants, the immunogenicity is 73% higher than that of the 13-valent vaccine;Although the 20-valent vaccine covers more serotypes, its protection against serotype 3 is no greater than that of the 13-valent and 15-valent vaccines; for the time being, it is only available for adults in Hong Kong.The Committee has therefore updated its vaccination recommendations to replace the 13-valent vaccine with the 15-valent vaccine, primarily because the latter offers higher immunogenicity against serotype 3 than both the 13-valent and 20-valent vaccines, and is believed to provide more effective protection against serotype 3 pneumococci.

Currently, children can receive two doses of the pneumococcal vaccine at 2 and 4 months of age, followed by a booster dose at 12 months. If a child has previously received three or four doses of the 7-valent, 10-valent, or 13-valent vaccine, parents can consult a doctor about whether to administer a dose of the 15-valent vaccine for targeted protection.