Immunity gaps for several vaccine preventable diseases in Norway

Childhood immunisation programs (CIP) have led to a substantial reduction in vaccine preventable diseases. However, simply monitoring a decline in disease incidence does not accurately reflect an individual's immunity to each disease. To identify the immune status in the Norwegian population, we measured the IgG levels against antigens of 7 vaccine preventable diseases (diphtheria, tetanus, pertussis (DTP), measles, mumps, rubella and Hemophilus influenzae type b infection) in 3051 residual sera representative of the Norwegian population aged 2-95 years in 2012. We found that 39.8% of women and 25.0% of men born before the launch of the CIP in 1952 (i.e. ≥60 years) had IgG antibody levels below the protective threshold for diphtheria, and 76.5% and 41.7% for tetanus, respectively. Among children, 20.7% had low IgG levels against diphtheria and 25.0% had low levels against tetanus at age six years, prior to the DTP booster dose at age seven. When we applied a suggested cutoff for protection of 5 IU/ml for IgG antibodies against pertussis toxin, 76.4% of children aged 6 years fell below this level, as did about 53.3% of teenagers aged 16 years, and 32.3% of individuals aged 60 year or older. For measles and rubella, we found adequate levels of IgG in all age groups, whereas IgG levels against mumps were close to a suggested threshold for protection. The highest IgG levels for measles, mumps and rubella were observed in adults from the age of 40 years, most of whom have likely experienced the diseases and have probably never been vaccinated. In conclusion, we demonstrate low IgG levels against diphtheria and tetanus both in children and in individuals over 60 years of age. Our findings may be an argument for rescheduling of the DTP booster in the CIP and for including DTP vaccines in the adult vaccination program.