Rapid Disappearance of Poliovirus Type 2 (PV2) Immunity in Young Children Following Withdrawal of Oral PV2-Containing Vaccine in Vietnam

Immunogenicity and lot-to-lot consistency of booster shot with Sabin inactivated poliomyelitis vaccine in Chinese children aged 18-24 Months: A phase Ⅳ clinical trial

BACKGROUND

There has been no data on the immunogenicity and safety of the 4th booster dose of the sIPV immunization in 18-24 months old children in post-marketing studies of large cohort providing with robust results.

METHOD

In a phase Ⅳ randomized, double-blinded clinical trial, 1200 participants aged 2 months were immunized with three consecutive doses of sIPV at 2, 3, and 4 months old to complete primary immunization. Out of the 1200 participants, 1129 received the 4th dose of sIPV as booster immunization. Immunogenicity was evaluated in 1100 participants.

RESULTS

Seropositive rates of the anti-poliovirus type 1, 2, and 3 neutralizing antibodies were 99.9 %, 98.0 %, 98.2 %, respectively, with GMTs of 557.0, 146.1, 362.0 one year after primary vaccination. After booster vaccination between 18 and 24 months old, the seropositive rates for 3 types all reached 100.0 %, with GMTs of 8343.6, 5039.6, 5492.0, respectively. Particularly for the anti-poliovirus type 2 antibody, the GMT was 230.4 after primary immunization, maintained to 146.1 one year after primary immunization, and increased to as high as 5039.6 after booster vaccination. The GMT ratios between each batch groups after booster immunization were between 0.67 and 1.50, meeting the immunological equivalence criteria. The incidence rate of adverse reaction was 23.0 %, which was comparable to those in the phase Ⅲ trial but had a lower incidence. Furthermore, no SUSAR was reported in this study.

INTERPRETATION

In conclusion, as the anti-poliovirus antibodies gradually waned one year post sIPV primary vaccination, especially the type 2 antibody waned to a very low level, suggesting the importance of the booster immunization for children at the age of 18-24 months old. The booster shot can greatly enhance the antibody level and protect children from the potential risk of infection with WPV and VDPV by supplementing the anti-poliovirus type 2 immunity gap in the current real world. Clinic Trial Registration. NCT04224519.

Strengthened surveillance revealed a rapid disappearance of the poliovirus serotype 2 vaccine strain in Madagascar after its removal from the oral polio vaccine

To assess circulation of the Sabin 2 poliovirus vaccine strain in Madagascar after its withdrawal from the oral polio vaccine in April 2016, a reinforced poliovirus surveillance was implemented in three regions of Madagascar from January 2016 to December 2017. Environmental samples and stool specimens from healthy children were screened using the Global Polio Laboratory Network algorithm to detect the presence of polioviruses. Detected polioviruses were molecularly typed and their genomes fully sequenced. Polioviruses were detected during all but 4 months of the study period. All isolates were related to the vaccine strains and no wild poliovirus was detected. The majority of isolates belong to the serotype 3. The last detection of Sabin 2 occurred in July 2016, 3 months after its withdrawal. No vaccine-derived poliovirus of any serotype was observed during the study. Only few poliovirus isolates contained sequences from non-polio origin. The genetic characterization of all the poliovirus isolates did not identify isolates that were highly divergent compared to the vaccine strains. This observation is in favor of a good vaccine coverage that efficiently prevented long-lasting transmission chains between unvaccinated persons. This study underlines that high commitment in the fight against polioviruses can succeed in stopping their circulation even in countries where poor sanitation remains a hurdle.

Outbreaks of Circulating Vaccine-derived Poliovirus in the World Health Organization Western Pacific Region, 2000-2021

The World Health Organization Western Pacific Region (WPR) has maintained the polio-free status for more than two decades. At the global level, there were only 6 confirmed polio cases due to wild type 1 poliovirus in Pakistan, Afghanistan, and Malawi in 2021, therefore, the risk of the importation of wild poliovirus from the endemic countries to the WPR is considerably lower than ever before. On the other hand, the risk of polio outbreaks associated with circulating vaccine-derived polioviruses (cVDPVs) still cannot be ignored even in the WPR. Since late 2010s, cVDPV outbreaks in the WPR have appeared to be more extensive in frequency and magnitude. Moreover, the emergence of concomitant polio outbreaks of type 1 and type 2 cVDPVs in the Philippines and Malaysia during 2019-2020 has highlighted the remaining risk of cVDPV outbreaks in high-risk areas and/or communities in the WPR. The previous cVDPV outbreaks in the WPR have been rapidly and effectively controlled, however, the future risk of polio outbreaks associated with cVDPVs needs to be reconsidered and polio immunization and surveillance strategies should be updated accordingly.

Inactivated Poliovirus Vaccine Closing the Type 2 Immunity Gap in Vietnam

This was a cross-sectional community-based serological survey of polio antibodies assessing the immunogenicity of inactivated poliovirus vaccine (IPV) focusing on poliovirus serotype 2. IPV was administered to 5-month-old children. Type 2 antibody seroprevalence when measured 1 month after IPV administration was >95%. One IPV dose successfully closed the immunity gap.

Indian Academy of Pediatrics (IAP) Advisory Committee on Vaccines and Immunization Practices (ACVIP): Recommended Immunization Schedule (2020-21) and Update on Immunization for Children Aged 0 Through 18 Years

Justification

In view of new developments in vaccinology and the availability of new vaccines, there is a need to revise/review the existing immunization recommendations.

Process

Advisory Committee on Vaccines and Immunization Practices (ACVIP) of Indian Academy of Pediatrics (IAP) had a physical meeting in March, 2020 followed by online meetings (September-October, 2020), to discuss the updates and new recommendations. Opinion of each member was sought on the various recommendations and updates, following which an evidence-based consensus was reached.

Objectives

To review and revise the IAP recommendations for 2020–21 and issue recommendations on existing and new vaccines.

Recommendations

The major changes include recommendation of a booster dose of injectable polio vaccine (IPV) at 4–6 years for children who have received the initial IPV doses as per the ACVIP/IAP schedule, re-emphasis on the importance of IPV in the primary immunization schedule, preferred timing of second dose of varicella vaccine at 3–6 months after the first dose, and uniform dosing recommendation of 0.5 mL (15 µg HA) for inactivated influenza vaccines.

Implication of a High Risk for Type 2 Vaccine-Derived Poliovirus Emergence and Transmission After the Switch From Trivalent to Bivalent Oral Poliovirus Vaccine

BACKGROUND

China implemented the globally synchronized switch from trivalent oral poliovirus vaccine (tOPV) to bivalent OPV (bOPV) and introduced 1 dose of inactivated poliovirus vaccine on 1 May 2016. We assessed the impact of the switch on the immunity level against poliovirus, especially type 2.

METHODS

Children born between 2014 and 2017, who were brought to the hospitals in Urumqi city, Xinjiang Province in 2017, were enrolled and blood samples were collected to test for antibody titers against poliovirus. A comparison of seroprevalence between the children born before (preswitch group) and after the switch (postswitch group) was performed to assess the impact of the switch on the immunity level against polio.

RESULTS

A total of 172 subjects were enrolled. The overall seroprevalences were 98.8%, 79.1%, and 98.3% for types 1, 2, and 3, respectively. Seroprevalence for type 2 significantly decreased from 91.6% in the preswitch group to 67.4% in the postswitch group, but no statistically significant change was observed for both types 1 and 3.

CONCLUSIONS

The switch from tOPV to bOPV can provide high-level immunity against types 1 and 3 but not against type 2, indicating a high risk of type 2 vaccine-derived poliovirus emergence and transmission.

One-Year Decline of Poliovirus Antibodies Following Fractional-Dose Inactivated Poliovirus Vaccine

BACKGROUND

Fractional dose (one-fifth of full intramuscular dose) of inactivated poliovirus vaccine (fIPV) administered intradermally is used as IPV dose-sparing strategy. We compared the rate of decline of poliovirus antibodies (PVA) in recipients of 2 doses of fIPV or IPV.

METHODS

A community-based randomized controlled trial was conducted in Karachi, Pakistan. Children aged 14 weeks were randomized into fIPV or full IPV (study arms A, B) and received 1 vaccine dose at age 14 weeks and 1 at age 9 months. PVAs were measured at age 14, 18 weeks and 10, 21 months.

RESULTS

Seroprevalence of poliovirus type 2 antibodies in 170/250 (68%) children after 2 IPV or fIPV doses at age 10 months in A and B reached 100% vs 99% (P = .339), and at 21 months, 86% vs 67% (P = .004). Between age 10 and 21 months antibody log2 titers dropped from ≥ 10.5 to 6.8 in A and from 9.2 to 3.7 in B.

CONCLUSIONS

There was a significant decline in antibody titers 12 months following the second IPV dose. The slope of decline was similar for full IPV and fIPV recipients. The results provide further evidence that fIPV is a viable option for IPV dose-sparing.

CLINICAL TRIALS REGISTRATION

NCT03286803.

Immunogenicity and safety of the inactivated poliomyelitis vaccine made from Sabin strains in a phase IV clinical trial for the vaccination of a large population

As a recently launched novel vaccine used as one of the vaccines for the final eradication of polios worldwide, complete data on the consistency and immunogenicity characteristics of the inactivated poliomyelitis vaccine made from the Sabin strain (sIPV) and its safety in large-scale populations are required to support the future use of this vaccine worldwide. A phase IV clinical trial was conducted to perform an immunogenicity evaluation of lot-to-lot consistency of three commercial batches of sIPV in 1200 infants and to investigate the vaccine's safety on a large-scale in 20,019 infants for active monitoring and 29,683 infants for passive monitoring through the Adverse Event Following Immunization (AEFI) reporting system in China. In the immunogenicity evaluation, the average seroconversion rates for type I, type II and type III of the three groups were 99.83%, 98.93% and 99.44%, respectively. No differences in the seroconversion rate and the GMT ratios were noted in the pair-to-pair comparisons. In the large-scale safety evaluation, most adverse reactions occurred 0-30 days after the first doses, and the common local and systemic reactions were similar to those in the phase III clinical trial, with low incidence in both activated and passive monitoring. In conclusion, sIPV exhibits good lot-to-lot consistency and safety in large-scale populations; thus, it is qualified to serve as one of the vaccines for use in eradicating all wild and vaccine-derived polioviruses worldwide in the near future. Clinic Trial Registration. NCT04224519 and NCT04220515.

Indian Academy of Pediatrics (IAP) Advisory Committee on Vaccines and Immunization Practices (ACVIP): Recommended Immunization Schedule (2020-21) and Update on Immunization for Children Aged 0 Through 18 Years

JUSTIFICATION

In view of new developments in vaccinology and the availability of new vaccines, there is a need to revise/review the existing immunization recommendations.

PROCESS

Advisory Committee on Vaccines and Immunization Practices (ACVIP) of Indian Academy of Pediatrics (IAP) had a physical meeting in March, 2020 followed by online meetings (September-October, 2020), to discuss the updates and new recommendations. Opinion of each member was sought on the various recommendations and updates, following which an evidence-based consensus was reached.

OBJECTIVES

To review and revise the IAP recommendations for 2020-21 and issue recommendations on existing and new vaccines.

RECOMMENDATIONS

The major changes include recommendation of a booster dose of injectable polio vaccine (IPV) at 4-6 years for children who have received the initial IPV doses as per the ACVIP/IAP schedule, re-emphasis on the importance of IPV in the primary immunization schedule, preferred timing of second dose of varicella vaccine at 3-6 months after the first dose, and uniform dosing recommendation of 0.5 mL (15 µg HA) for inactivated influenza vaccines.

Plans for Nationwide Serosurveillance Network in Vietnam

In recent years, serosurveillance has gained momentum as a way of determining disease transmission and immunity in populations, particularly with respect to vaccine-preventable diseases. At the end of 2017, the Oxford University Clinical Research Unit and the National Institute of Hygiene and Epidemiology held a meeting in Vietnam with national policy makers, researchers, and international experts to discuss current seroepidemiologic projects in Vietnam and future needs and plans for nationwide serosurveillance. This report summarizes the meeting and the plans that were discussed to set up nationwide serosurveillance in Vietnam.