Independent report

Joint Committee on Vaccination and Immunisation statement on vaccination strategy for the ongoing polio incident

Published 10 August 2022

The Joint Committee on Vaccination and Immunisation (JCVI) met on 25 July 2022 to discuss the ongoing polio incident and to advise on the vaccination strategy to control the ongoing incident.

Background

The National Institute for Biological Standards and Control (NIBSC) of the Medicines and Healthcare products Regulatory Agency (MHRA) conducts routine environmental surveillance for wild type and vaccine-like polio viruses as part of the UK’s commitment to the World Health Organization (WHO) global polio eradication programme. Vaccine-like type-2 poliovirus (PV2) isolates were found in sewage samples collected from the London Beckton sewage treatment works in February 2022 and have persisted since. This is unusual activity and analysis has shown that all PV2 isolates identified since then are genetically related to each other. There are indications of person-to-person community transmission of poliovirus. Wastewater samples from Glasgow were also routinely evaluated where poliovirus has not yet been detected.

The Beckton sewage treatment plant covers a large catchment area with a population close to 4 million across north-east and north-central London. As expected, between February and May, the virus has evolved (whereby the virus has acquired mutations to reverse the attenuation properties of vaccine strains) and has now met the criteria of a vaccine-derived poliovirus (VDPV2). VDPVs behave more like wild-type virus, can sustain outbreaks and on rare occasions lead to paralytic presentations in unvaccinated individuals.

It is considered most likely that an individual entered the UK in February 2022 (or before) from a country where oral polio vaccine (OPV) has been used for supplementary immunisation campaigns and outbreak response. Recently vaccinated individuals shed the OPV virus in their stool for a few weeks after and this can be detected through the sewage surveillance. The UK switched from using OPV to inactivated polio vaccine (IPV) in 2004, the year after poliovirus was declared eradicated in the WHO European region.

In July 2022, a case of paralytic poliovirus (type 2) was reported in New York state in an unvaccinated adult male; and in March 2022 WHO was notified of the detection of circulating VDPV3 and resulting paralysis in an unvaccinated 3-year-old child in Israel.

The UK Health Security Agency (UKHSA) is urgently investigating the extent of transmission of the virus across north-east and north-central London. Further upstream sampling has been undertaken and poliovirus has now been identified to be present at least one positive sample in several boroughs: Barnet, Brent, Camden, Enfield, Hackney, Haringey, Islington and Waltham Forest.

The virus has also been detected in lower concentrations and frequency in areas adjacent to the Beckton catchment area to the north (Enfield and Barnet), south (immediately south of the Thames) and east. It is not yet clear, however, whether virus circulation is established in these areas or whether the detection of virus could result from people commuting or travelling from the affected area. The level of PV2 found and the high genetic diversity among the PV2 isolates suggests that there is virus transmission in separate networks of individuals in these 5 boroughs and possibly in some of the other surrounding areas. The pattern is not consistent with virus shedding by one or few individuals.

Vaccination coverage for the 3-dose primary schedule in one year olds in London is well below the average achieved for the UK and uptake of the pre-school booster in 5 year olds is even lower. This falls below the WHO target of 95% coverage. The high-density population in the areas affected and the number of individuals under-vaccinated in those boroughs suggests that there is significant potential for the VDPV2 to continue to spread. Under-vaccinated children can become infected and pass infection on to others. There is significant overlap between the local authorities with the lowest vaccine coverage and where VDPV2 has been detected (UKHSA COVER data, 2021 to 2022).

Non-immune children are at risk of paralysis from VDPV2 and there is therefore an urgency to ensure that unvaccinated children have access to vaccine.

Individuals born before 2004 will have been eligible for OPV vaccination – this vaccine provides good protection against polio and also provides high levels of gut immunity. Individuals born after 2004 in the UK will have received IPV, which provides excellent protection from severe polio but individuals can still become infected and spread polio virus without exhibiting any symptoms. Currently, hexavalent DTaP/IPV/Hib/HepB vaccine is offered routinely to babies at 8, 12 and 16 weeks of age. Further doses of polio containing vaccines are given at the age of 3 years and 4 months as part of the pre-school booster (dTaP/IPV) and at around 14 years old (Td/IPV) as part of the teenage booster.

As part of the maternal pertussis vaccination programme, introduced in 2012, a dose of polio containing vaccine (dTaP/IPV) is also given in pregnancy. The National Vaccine Evaluation Consortium (NVEC) iMAP2 study showed that maternal pertussis vaccination provides high levels of antibody against pertussis, tetanus, diphtheria to young infants. This provides high levels of protection against whooping cough, and the successful programme has been shown to reduce the risk of infant deaths from this disease (Ladhani and others 2015, Amirthalingam and others 2014). It is estimated that the maternal pertussis programme has prevented between 82 and 170 infant deaths between 2012 and 2017 (Sandmann and others 2020).

Unpublished evidence from the NVEC study suggests that these high antibody levels may reduce the infant’s response to IPV when measured at 12 months. The clinical significance of this finding is not clear, but the lower antibody level is likely to persist up until the administration of the pre-school IPV booster at 3 years 4 months, and children who miss this booster dose may remain susceptible. Lower uptake of the booster is especially common in affected areas of London. It is therefore plausible that the somewhat lower antibody levels might be less good at preventing VDPV2 transmission. It is anticipated that this potential immunity gap will be corrected by the administration of a polio containing vaccine to children aged one year and above, as maternal antibodies will no longer interfere with the active immune response. There are no planned changes to the maternal pertussis immunisation programme and it is still recommended for those who are pregnant.

UKHSA has declared a national enhanced incident response to coordinate the investigation and response to the polio incident. National polio guidelines outline the public health considerations when a VDPV2 is detected in environmental samples. WHO has been alerted and UKHSA continues to keep them updated with developments.

The NHS is strengthening ongoing work to improve uptake nationally in the routine childhood programme. In London, active call and recall of unvaccinated and partially vaccinated children under the age of 5 is already underway through primary care, with a planned phased extension up to 18 years of age. Due to the large pool of partially vaccinated or unvaccinated individuals in the affected areas of London it is highly unlikely that the IPV catch-up alone will be sufficient to prevent cases of paralysis or control the VDPV2 spread.

Advice for an IPV vaccination campaign

The JCVI agreed that the most immediate priority is to ensure all eligible individuals are up to date with their polio (IPV) vaccinations and they endorsed the current NHS efforts to increase coverage of the routine childhood vaccination programme nationally alongside the proactive catch-up of partially vaccinated and unvaccinated children in London.

Due to the nature of this public health emergency the JCVI agreed that an urgent supplemental vaccination strategy is required to:

• prevent cases of paralysis due to poliovirus
• interrupt transmission of VDPV2 in the community

The JCVI advised that, in addition to ongoing catch-up, a supplementary IPV booster campaign should be implemented for children aged 1 to 9 years in London. The additional dose of IPV will help to ensure that there is a high level of protection from paralysis in the area where the VDPV2 is circulating. A focused campaign approach is likely to lead to higher vaccine coverage and will facilitate outreach to under-served communities.

The booster campaign may also contribute to interrupting transmission of VDPV2 in the community. Children under 10 years of age are likely to be the focus of transmission because of lower levels of personal hygiene, and are likely to have lower levels of polio antibodies as discussed above. Offering an additional dose to those who are vaccinated will boost antibody levels and may help to reduce or curtail asymptomatic excretion of the virus.

This campaign should start as soon as possible in the London boroughs where VDPV2 has been detected and then be expanded to all London boroughs.

All IPV containing vaccines have the same polio content and will provide an excellent boost across the whole age range. Based on existing approvals and to allow an immediate response to be implemented, 3 different products are recommended as follows:

• children aged 1 to under 3 years 4 months are offered the hexavalent (DTaP/IPV/Hib/HepB) vaccine (both Infanrix Hexa© and Vaxelis© to be used)
• children aged 3 years 4 months up to and including 5 year olds are offered Boostrix-IPV© (dTaP/IPV)
• children aged 6 to 9 years are offered Revaxis© (Td/IPV)

The booster campaign should target all children aged 1 to 9 years. UKHSA will publish accompanying clinical guidance on eligibility.

The JCVI recommended that the impact of the IPV campaign should be evaluated through monitoring of coverage (including inequalities), continued environmental surveillance, and enhanced surveillance of paralytic polio presentations. Other studies may be needed, such as stool surveys to determine whether further interventions are required. Environmental sample and vaccine coverage data from across the UK will inform any further policy response.

Due to the nature of this public health emergency, timeliness of response is of vital importance to reduce transmission and avoid paralytic cases of poliovirus occurring. The JCVI advised that the IPV booster campaign should be prioritised alongside other planned time-sensitive immunisation programmes including COVID-19 and seasonal influenza.

If the risk status changes, the JCVI will consider if further action, including a campaign using novel OPV2 (nOPV2) vaccine is required. Preparatory work to enable the UK to access the nOPV2 vaccine through WHO is underway.

The JCVI also discussed the possibility of bringing forward the planned change to the routine infant schedule. As Hib/MenC vaccine is no longer being manufactured, the JCVI has already considered replacing this vaccine with an additional dose of the hexavalent vaccine (DTaP/IPV/Hib/HepB) (either at 12 or 18 months). The additional hexavalent vaccine dose in the second year of life would also address the potential polio immunity gap that has emerged due to the maternal pertussis vaccination programme. Although this change to the schedule was originally proposed to take effect in 2025, the JCVI advised that following on from the planned IPV booster campaign, London should bring forward the planned change to shortly after the IPV booster campaign has completed to ensure continued protection of future cohorts of toddlers.

UKHSA will continue to closely monitor emerging evidence around the polio incident and the control measures deployed and the JCVI will issue further advice on interventions if required.

References

Polio: national guidelines

UKHSA cover of vaccination evaluated rapidly (COVER) programme 2021 to 2022: quarterly data

Complete routine immunisation schedule

Data from National Vaccine Evaluation Consortium (NVEC) iMAP2 study.

Ladhani SN, Andrews NJ, Southern J, Jones CE, Amirthalingam G, Waight PA, England A, Matheson M, Bai X, Findlow H, Burbidge P, Thalasselis V, Hallis B, Goldblatt D, Borrow R, Heath PT, Miller E. Antibody responses after primary immunization in infants born to women receiving a pertussis-containing vaccine during pregnancy: single arm observational study with a historical comparator. Clin Infect Dis. 2015 Dec 1;61(11):1637-44. doi: 10.1093/cid/civ695. Epub 2015 Sep 15. Erratum in: Clin Infect Dis. 2016 Jun 15;62(12 ):1621. PMID: 26374816.

Amirthalingam G, Andrews N, Campbell H, Ribeiro S, Kara E, Donegan K, Fry NK, Miller E, Ramsay M. Effectiveness of maternal pertussis vaccination in England: an observational study. Lancet. 2014 Oct 25;384(9953):1521-8. doi: 10.1016/S0140-6736(14)60686-3. Epub 2014 Jul 15. PMID: 25037990.

Sandmann F, Jit M, Andrews N, Buckley HL, Campbell H, Ribeiro S, Sile B, Stowe J, Tessier E, Ramsay M, Choi YH, Amirthalingam G. Infant hospitalisations and fatalities averted by the maternal pertussis vaccination programme in England, 2012-2017: Post-implementation economic evaluation. Clin Infect Dis. 2020 Oct 71 (8): 1984 to 1987.