Sabin Vaccine in Poliomyelitis Eradication: Achievements and Risks

Implementation challenges and real-world impacts of switching pediatric vaccines: A global systematic literature review

Switching a vaccine for another on a pediatric national immunization program is often done for the betterment of society. However, if poorly implemented, switching vaccines could result in suboptimal transitions with negative effects. A systematic review was conducted to evaluate the existing knowledge from identifiable documents on implementation challenges of pediatric vaccine switches and the real-world impact of those challenges. Thirty-three studies met the inclusion criteria. We synthesized three themes: vaccine availability, vaccination program deployment, and vaccine acceptability. Switching pediatric vaccines can pose unforeseen challenges to health-care systems worldwide and additional resources are often required to overcome those challenges. Yet, the magnitude of the impact, especially economic and societal, was frequently under-researched with variability in reporting. Therefore, an efficient vaccine switch requires a thorough consideration of the added benefits of replacing the existing vaccine, preparation, planning, additional resource allocation, implementation timing, public-private partnerships, outreach campaigns, and surveillance for program evaluation.

Circulating vaccine derived polio virus type 1 outbreak, Saadah governorate, Yemen, 2020

Background

Yemen has faced one of the worst humanitarian crises in the world since the start of the war in 2015. In 2020; 30 Vaccine Derived Polio Virus type 1 (VDPV1) isolates were detected in Saadah governorate. The aims are to characterize the outbreak and address the gaps predisposing the emergence and circulation of VDPV1 in Saadah governorate, Yemen.

Method

A retrospective descriptive study of confirmed cases of VDPV1 between January and December 2020 was performed. Surveillance staff collected data from patient cases, contacts, as well as stool specimens that shipped to WHO accredited polio labs. Data of population immunity was also reviewed. The difference in days between the date of sample collection, shipment, and receiving lab result was used to calculate the average of delayed days for lab confirmation.

Results

From January to December 2020, a total of 114 cases of acute flaccid paralysis (AFP) were reported from 87% (13/15) districts, and cVDPV1 was confirmed among 26% (30) AFP cases. 75% (21) were < 5 years, 73% (20) had zero doses of Oral Polio Vaccine (OPV). The first confirmed case (3%) was from Saadah city, with paralysis onset at the end of January 2020 followed by 5 cases (17%) in March from another four districts, 8 cases (27%) in April, and 13 (43%) up to December 2020 were from the same five districts in addition to 3 (10%) form three new districts. The lab confirmation was received after an average of 126 days (71–196) from sample collection. The isolates differ from the Sabin 1 type by 17- 30 VP1 nucleotides (nt) and were linked to VDPV1 with 13 (nt) divergence that isolated in July 2020 from stool specimens collected before one year from contacts of an inadequate AFP case reported from Sahar district.

Conclusion

The new emerging VDPV1 was retrospectively confirmed after one year of sample collection from Sahar district. Delayed lab confirmation, as well as the response and low immunization profile of children against polio, were the main predisposing factors for cVDPV1 outbreak. This outbreak highlights the need to maintain regular biweekly shipments to referral polio labs in the short-term, and the exploration of other options in the longer-term to enable the Yemen National Lab to fully process national samples itself.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07397-0.