Vaccines to Children – Protective Effect and Adverse Events

SBU’s Conclusions

Few medical interventions have had as great an impact on global health as immunisation of children. Extensive immunisation programmes have eradicated smallpox completely and eliminated polio in all but a handful of countries. Thus, the benefits of immunisation are indisputable. But it is important to critically examine an intervention that is recommended for all infants. Routine immunisation must provide reasonable protection against potentially serious diseases, while the risk of serious adverse events must be low. Experience shows that immunisation coverage tends to decline if there is widespread concern about adverse events. Therefore, a solid body of knowledge is needed. Thus, SBU has been requested to review the published scientific literature regarding some vaccines included in the immunisation programme for children in Sweden.

The present scientific review and the experience from many years of the routine immunisation programme have shown that:

• The benefits of immunisation far outweigh the risks of adverse events.
• Immunisation has virtually eliminated the morbidity and mortality of many diseases previously common among both children and adults.

Immunisation with Haemophilus Influenzae type b Vaccine

• Immunisation with Haemophilus influenzae type b (Hib) vaccine effectively protects against Hib infections, which can be serious (Evidence Grade 1). The protective effect lasts at least three years. Immunisation against Hib reduces carriage of Hib in the pharynx of children (Evidence Grade 3). Routine immunisation of infants also reduces the frequency of serious Hib infections in unvaccinated individuals, so called herd immunity (Evidence Grade 3). There is no data suggesting a causal relationship between Hib conjugate vaccines and serious adverse events such as death, sudden infant death syndrome, seizures, type 1 diabetes mellitus and Guillain-Barré syndrome, a neurological disease.

Immunisation with Pertussis Vaccine

• Immunisation with pertussis vaccine protects children against pertussis (Evidence Grade 1). The protective effect lasts at least 5 years after three or four doses of acellular pertussis vaccine (Evidence Grade 3). Routine immunisation programmes that include acellular pertussis vaccine reduce the need of hospitalisation due to pertussis among vaccinated children younger than 2 years of age (Evidence Grade 3). There is no evidence of a higher frequency of or deaths from serious bacterial infections after immunisation with acellular pertussis vaccine (Evidence Grade 1). The scientific literature provides no substantial indication of a causal relationship between acellular pertussis vaccine and the few serious adverse events described in case reports or in national adverse event reports. Health economic models show that immunisation against pertussis is socioeconomically warranted. However, the cost-benefit ratio varies substantially according to assumptions on incidence of pertussis, vaccine efficacy and percentage of immunised children.

Immunisation with Measles-Mumps-Rubella Vaccine

• Combination measles-mumps-rubella (MMR) vaccines currently in use provides protection against all three diseases and their complications (Evidence Grade 3).
• MMR vaccine increases the risk of febrile seizures during the first two weeks after immunisation, when fever commonly occurs, but does not increase the risk of later epilepsy (Evidence Grade 3). MMR vaccine does not cause type 1 diabetes or serious infections requiring hospitalisation (Evidence Grade 3). MMR vaccine does not cause autism or autism spectrum disorder (Evidence Grade 3).

Immunisation with Hepatitis B Vaccine

• Immunisation with hepatitis B vaccine protects children against hepatitis B (Evidence Grade 1). More than 90% of immunised children develop protective antibody levels after the first dose (Evidence Grade 1). Serious hypersensitivity reactions have been reported following hepatitis B immunisation, but very rarely. There is insufficient scientific evidence to rule out or confirm a association between hepatitis B immunisation and multiple sclerosis (MS). Available data taken together suggest that there is no such correlation. The literature provides no substantial indication of a causal relationship between hepatitis B vaccine and other serious adverse events described in case reports: death, neurological disease other than MS, arthritis and chronic fatigue syndrome. Health economic models indicate hepatitis B vaccine to be cost-effective from a healthcare perspective.

Immunisation Against Tuberculosis

• Bacille Calmette-Guérin (BCG) vaccine administered during the neonatal period or shortly thereafter protects children against tuberculosis at least until 5 years of age. Protection against all forms of tuberculosis is approximately 75% (Evidence Grade 2). Efficacy against disseminated (miliary) tuberculosis and tuberculous meningitis is higher around 75 to 85% (Evidence Grade 2). Fatal disseminated BCG infection occurs after BCG immunisation, but very rarely (Evidence Grade 1). The risk is approximately 1 case per 100 000 immunised infants. The condition is mainly contracted by children with a rare genetic immunodeficiency disease that also increases the risk for other diseases. To further reduce the risk of this serious but rare adverse event, BCG immunisation in Sweden is deferred till 6 months of age, allowing time to identify infants with this rare immunodeficiency disease and exclude them from BCG immunisation.

Adverse Events Following Combination Vaccines

• There is no indication of clinically significant differences in the frequency of redness, swelling or fever after administration of vaccines that contain different combinations of the following vaccines: diphtheria (D), tetanus (T), pertussis (Pa), polio (IPV), hepatitis B (HBV) and Haemophilus influenzae type b (Hib) (hexavalent vaccine; DTPa-IPV-HBV/Hib, pentavalent vaccine; DTPa-IPV/Hib, tetravalent vaccine; DTPa-IPV or trivalent vaccine; DTPa) (Evidence Grade 2).

No evidence is available suggesting a greater frequency of hypotonic hyporesponsive episode or persistent inconsolable crying after administration of combination hexavalent, pentavalent or tetravalent vaccine than trivalent vaccine (DTPa) (Evidence Grade 3). The overall literature provides no substantial indication of a causal relationship between immunisation and the very occasional serious adverse events, including death, described in case reports or national adverse event reports (insufficient scientific evidence).