Thirty five years after the certification of smallpox eradication, another partial success of the World Health Assembly (WHA) was reached: On 20th September 2015, the global eradication of wild PV2 (WPV), and on 24th October 2019, the global eradication of wild PV3 was declared [1,2]. In 1988, the WHA resolved to eradicate polio worldwide, and remarkable progress was achieved due to effective vaccination. The live-attenuated oral polio vaccine (OPV) was recommended in the German Democratic Republic in 1960 and the Federal Republic of Germany in 1962. Because of decreasing cases of poliomyelitis and vaccine-derived side effects, the vaccine strategy in Germany was switched from OPV to inactivated poliovirus vaccine (IPV) in 1998 [3]. The last indigenous polio case in Germany was reported in 1990 [4]. Currently, only Afghanistan and Pakistan are reporting endemic WPV transmissions [5]. In the context of the coronavirus disease 2019 pandemic n.172 confirmed wild-type PV cases were reported from 2020 to December 2022 from these countries, however, it is believed that substantial national and subnational surveillance gaps exist and case numbers in Pakistan are on the rise at the end of 2022 [6,7]. Unfortunately, not only WPV can cause paralytic symptoms. In Regions with low polio immunity, circulating vaccine-derived polioviruses (cVDPV) can also cause outbreaks, mostly related to cVDPV2 (n=491 cases from December 2021 to December 2022 [8]). Recently, vaccine-derived paralytic polio cases were reported from Pidie, Indonesia, New York, U.S.A. and Jerusalem, Israel (all countries previously certified polio-free), for the latter two cVDPV could also be detected in wastewater, including London, U.K., highlighting the need of sustaining polio vaccination [9], [10], [11], [12], [13], [14]. As the last WPV2 was detected in 1999 and to avoid cVDPV2, a global switch from trivalent live-attenuated polio vaccine (tOPV) to a bivalent formulation (bOPV1+3) was conducted in April 2016, and a novel oral polio vaccine type 2 (nOPV2) to address outbreaks of cVDPV2 has been launched in March 2021 [15,16]. After stopping the circulation of any PV2 and PV3, laboratories or vaccine manufacturing plants may be the only source of virus- release [17]. According to WHO containment plans, the use of PV2 is therefore restricted to certified polio essential facilities (PEF), and the full containment of PV3 is in transition and to be achieved due to 2025 [18,19]. In 2021, within the WHO European Region, only 25 of 53 countries reached third-dose polio vaccination rates of ≥95% [20]. The cVDPV might pose a problem for those who have not been vaccinated. Based on officially reported vaccine coverage data, this could affect up to 12 million people aged 0–29 years in Europe [21]. In the long term, the eradication of polio is considered likely cost-saving compared with permanent control [22]. Seroepidemiologic studies are important for evaluating the impact of vaccination programmes. They can help in the detection of unprotected individuals and inform decisions on adapting vaccine policy when necessary, mitigating the risk of future outbreaks [23].

The cell culture-based neutralising antibody test (NT) using “live poliovirus” is the method of choice to determine the polio immunity status. Additionaly, polio pseudovirus-based (high-throughput) capable NTs without using live poliovirus have recently been described [24], [25], [26]. Laboratories in Germany as well as in other countries use NTs for control of herd immunity and individual immunity against poliomyelitis. The omission of live PV2 and PV3 may cause uncertainty in reporting. To reveal a possible gap in PV2 and PV3 immunity, the NT results from two German labs (a university lab and a private lab, located in the central and southwest of Germany) were analysed. Data were obtained during 2005-2020 and the proportion of sera exclusively being negative for PV2 antibodies (whilst having antibodies against PV1 and PV3) as well as for PV1 and PV3 was determined.