Reduced reactogenicity of primary vaccination with DT3aP-HBV-IPV/Hib compared with DT2aP-HBV-IPV-Hib among infants: Mathematical projections in six countries.

Vaccination of infants against diphtheria, tetanus, pertussis, hepatitis B, poliomyelitis, and Haemophilus influenzae type b is often performed with combined vaccines against these six diseases. In many countries, these are the first vaccinations received by infants, and potential adverse reactions could affect compliance with future vaccinations. A previous study examined two of the combined vaccines, DT3aP-HBV-IPV/Hib and DT2aP-HBV-IPV-Hib, and showed that local adverse reactions at the injection site (pain, redness, and swelling) and general adverse reactions (fever, drowsiness, irritability, persistent crying, and lack of appetite) were less common after vaccination with DT3aP-HBV-IPV/Hib than with DT2aP-HBV-IPV-Hib.To understand the impact of this finding at a population level, we compared the adverse reactions caused by the hypothetical administration of the two vaccines under similar conditions. We simulated the vaccination of infants with both vaccines in six countries: Austria, the Czech Republic, France, Jordan, Spain, and the Netherlands.The simulation showed that the DT3aP-HBV-IPV/Hib vaccine could reduce cases of swelling at the injection site by 3% and fever by 10%. For the year 2020, the resulting reduction in the estimated number of fever occurrences would have ranged from over 7,000 in Austria to over 62,000 in France. In total, adverse reactions avoided could hypothetically have ranged from 30,781 in Austria to 269,025 in France. Over 5 years, this could have avoided an estimated number of adverse reactions of over 150,000 in Austria to over 1.4 million in France. In conclusion, such a switch of vaccine could substantially reduce adverse reactions.