Why we need one?
To get a better estimate of the circulation of B. pertussis in the population, seroprevalence studies have proven to be a valuable instrument next to the surveillance programs based on reporting systems. It is an accepted fact that the incidence numbers for pertussis based on the reporting systems from different countries within Europe cannot be compared. For example, the incidence of pertussis in European countries varies from 0.01 up to 50 per 100,000 inhabitants. Moreover, most natural infections among adolescents and adults due to B. pertussis result in mild or subclinical disease and are often not reported. It should be kept in mind that adults are the main source of transmission of pertussis to infants.
Together with ECDC, we have previously organized two seroprevalence studies during 2012-2013 and 2016-2017: the first one was conducted among age groups 20-39 years (childbearing age) in 14 EU/EEA countries and the second one among adults aged 40-59 years in 18 countries. In the latter, the proportion of individuals lacking the protective level of diphtheria antibodies (<0.1 IU/mL) varied between 22.8–82.0%, whereas for tetanus the protection was sufficient. For pertussis, the proportion of study subjects with specific anti-pertussis toxin (PT) antibody levels ≥100 IU/mL, indicative of recent exposure to pertussis was comparable for 13/18 countries, ranging between 2.7–5.8%. A similar proportion (0.2- 5.7%) with specific anti-PT antibodies ≥100 IU/mL was also observed in the first study.
What will be done this time?
During the EURL-PH-DIPE seven-year project, we will organize a seroprevalence study focusing on the successive age groups of 20–29, 30–39, 40-49, 50-59 and 60- 69. This task is aimed to study specific anti-DT (diphtheria toxin) and anti-PT antibodies. Additionally anti-TT (tetanus toxin) antibodies are measured.
Importance
This study will provide important information on waning immunity of adult age groups. It will also provide important information on whether the strategy “every 10 years booster for DT” as recommended by WHO is optimal. The results will likely identify the difference in population immunity between countries with and without adolescent and adult boosters against pertussis as well as the difference in population immunity between countries with and without maternal immunization against pertussis. To our knowledge, data on seroprevalence of anti-PT, anti-DT and anti-TT IgG antibodies in adults older than 60 years have not been reported in industrial countries.
In addition, the seroprevalence study may discover how the low exposure during COVID-19 pandemic lockdown and non-pharmacologic measures have affected the population immunity to pertussis and diphtheria (the results obtained can be directly compared to those from previous seroprevalence studies) in Europe. This is especially important as diphtheria cases have increased and there is a possibility for outbreaks. ECDC/EU can also share new guidance to member countries based on the activities and findings among this network. This will have a wide impact at European and international levels.