A national cross-sectional study for poliovirus seroprevalence in the Republic of Korea in 2012: implication for deficiency in immunity to polio among middle-aged people

Non-Polio Enteroviruses from Acute Flaccid Paralysis Surveillance in Korea, 2012-2019

The risk of polio importation and re-emergence persists since epidemic polio still occurs in some countries, and the resurgence of polio occurring almost 20 years after polio eradication was declared in Asia has been reported. We analyzed the results of acute flaccid paralysis (AFP) surveillance in Korea to assess the quality of AFP surveillance and understand the etiology of non-polio enterovirus (NPEV)-associated central nervous system diseases in a polio-free area. We investigated 637 AFP patients under 15 years of age whose cases were confirmed during 2012–2019 by virus isolation, real-time reverse transcription polymerase chain reaction, and VP1 gene sequencing. Among the 637 AFP cases, NPEV was detected in 213 (33.4%) patients, with the majority observed in EV-A71, with 54.9% of NPEV positives. EV-A71 has been shown to play a role as a major causative agent in most neurological diseases except for Guillain-Barré syndrome (GBS), acute disseminated encephalomyelitis (ADEM), and meningitis. This study provides information on the AFP surveillance situation in Korea and highlights the polio eradication stage in the monitoring and characterization of NPEV against the outbreak of neurological infectious diseases such as polio.

Seroprevalence of poliovirus antibodies before and after polio vaccine switch in 2012 and 2017 in Beijing

In 2000, China was declared polio-free. However, in 2018, wild poliovirus (WPV) was still endemic in two of its neighboring countries, making WPV importation and outbreak alarming possibilities. This study documents the seroprevalence of poliovirus antibodies before and after the polio vaccine switch in 2012 and 2017 in Beijing. Cross-sectional population-based serologic surveys were conducted in 2012 and 2017 in Beijing. The study subjects were selected from 10 different age groups (<1, 1-4, 5-9, 10-14, 15-19, 20-24, 25-29, 30-34, 35-39, and ≥40 y) using a multi-stage-stratified sampling method. Neutralizing antibody titers against poliovirus serotypes 1 (P1), 2 (P2), and 3 (P3) were assayed by World Health Organization standards. The seropositive rates (SR) and geometric mean titer (GMT) of the neutralizing antibodies were 91.71% and 1:130.26, respectively, for P1, 94.09% and 1:113.39, respectively, for P2, and 88.78% and 1:79.65, respectively, for P3 before the switch in 2012, and 87.78% and 1:108.93, respectively, for P1, and 81.67% and 1:70.56, respectively, for P3 after the switch in 2017, with a statistically significant difference for P1 and P3 between 2012 and 2017. The neutralizing antibodies for all poliovirus serotypes differed among different age and vaccination groups in both 2012 and 2017. After switching polio vaccines twice in 2014 and 2016, the P1 and P3 polio antibody levels were lower in 2017 than in 2012. The P2 antibody levels were determined from the first dose of IPV. The seroprevalence of poliovirus antibodies after adjustment of the immunization schedule of the polio vaccine on January 1, 2020, must be further monitored.

Lower immunity to poliomyelitis viruses in Australian young adults not eligible for inactivated polio vaccine

There are limited long-term data on seroprevalence of neutralising antibody (nAb) to the three poliovirus serotypes following the switch from oral polio vaccine (OPV) to inactivated polio vaccine (IPV). In Australia, combination vaccines containing IPV replaced OPV in late 2005. Using serum and plasma specimens collected during 2012 and 2013, we compared prevalence of nAb to poliovirus type 1 (PV1), type 2 (PV2) and type 3 (PV3) in birth cohorts with differing IPV and OPV eligibility from an Australian population-based sample. In the total sample of 1673 persons aged 12 months to 99 years, 85% had nAb against PV1, 83% PV2 and 67% PV3. In the cohort 12 to <18 years (eligible for 4 OPV doses, last dose 8-14 years prior), a significantly lower proportion had nAb than in the 7 to <12 year cohort (eligible for 3 OPV doses and an IPV booster, last dose 3-8 years prior) for all poliovirus types: [PV1: 87.1% vs. 95.9% (P = 0.01), PV2: 80.4% vs. 92.9% (P = 0.003) and PV3: 38.1% vs. 84.0% (P < 0.0001)]. These data suggest individual-level immunity may be better maintained when an OPV primary schedule is boosted by IPV, and support inclusion of an IPV booster in travel recommendations for young adults who previously received only OPV.

Polio vaccination coverage and seroprevalence of poliovirus antibodies after the introduction of inactivated poliovirus vaccines for routine immunization in Japan

In Japan, the oral poliovirus vaccine (OPV) was changed to 2 types of inactivated poliovirus vaccine (IPV), the standalone conventional IPV (cIPV) and the Sabin-derived IPV combined with diphtheria-tetanus-acellular pertussis vaccine (DTaP-sIPV), for routine immunization in 2012. We evaluated polio vaccination coverage and the seroprevalence of poliovirus antibodies using data from the National Epidemiological Surveillance of Vaccine-Preventable Diseases (NESVPD) from 2011 to 2015. Several years before the introduction of IPV in 2012, OPV administration for children was refused by some parents because of concerns about the risk of vaccine-associated paralytic poliomyelitis. Consequently, in children aged <1 years who were surveyed in 2011-2012, polio vaccination coverage (45.0-48.8%) and seropositivity rates for poliovirus (type 1: 51.7-65.9%, type 2: 48.3-53.7%, and type 3: 15.0-29.3%) were decreased compared to those surveyed in 2009. However, after IPV introduction, the vaccination coverage (95.5-100%) and seropositivity rates (type 1: 93.2-96.6%, type 2: 93.1-100%, and type 3: 88.6-93.9%) increased among children aged <1 years in 2013-2015. In particular, seropositivity rates and geometric mean titers (GMTs) for poliovirus type 3 in <5-year-old children who received 4 doses of IPV (98.5% and 247.4, respectively) were significantly higher than in those who received 2 doses of OPV (72.5% and 22.9, respectively). Furthermore, in <5-year-old children who received 4 doses of either DTaP-sIPV or cIPV, the seropositivity rates and the GMTs for all 3 types of poliovirus were similarly high (96.5-100% and 170.3-368.8, respectively). Our findings from the NESVPD demonstrate that both the vaccination coverage and seropositivity rates for polio remained high in children after IPV introduction.

Seroepidemiology: an underused tool for designing and monitoring vaccination programmes in low- and middle-income countries

Seroepidemiology, the use of data on the prevalence of bio-markers of infection or vaccination, is a potentially powerful tool to understand the epidemiology of infection before vaccination and to monitor the effectiveness of vaccination programmes. Global and national burden of disease estimates for hepatitis B and rubella are based almost exclusively on serological data. Seroepidemiology has helped in the design of measles, poliomyelitis and rubella elimination programmes, by informing estimates of the required population immunity thresholds for elimination. It contributes to monitoring of these programmes by identifying population immunity gaps and evaluating the effectiveness of vaccination campaigns. Seroepidemiological data have also helped to identify contributing factors to resurgences of diphtheria, Haemophilus Influenzae type B and pertussis. When there is no confounding by antibodies induced by natural infection (as is the case for tetanus and hepatitis B vaccines), seroprevalence data provide a composite picture of vaccination coverage and effectiveness, although they cannot reliably indicate the number of doses of vaccine received. Despite these potential uses, technological, time and cost constraints have limited the widespread application of this tool in low-income countries. The use of venous blood samples makes it difficult to obtain high participation rates in surveys, but the performance of assays based on less invasive samples such as dried blood spots or oral fluid has varied greatly. Waning antibody levels after vaccination may mean that seroprevalence underestimates immunity. This, together with variation in assay sensitivity and specificity and the common need to take account of antibody induced by natural infection, means that relatively sophisticated statistical analysis of data is required. Nonetheless, advances in assays on minimally invasive samples may enhance the feasibility of including serology in large survey programmes in low-income countries. In this paper, we review the potential uses of seroepidemiology to improve vaccination policymaking and programme monitoring and discuss what is needed to broaden the use of this tool in low- and middle-income countries.