India Switching from Oral Polio Vaccine to Inactivated Polio Vaccine

This article is a response to “The Oral Polio Vaccine Aimed at Global Eradication”. July 21, 2023by Vipin M. Vashshtha and Puneet Kumar.

In 2022, after more than a decade of polio-free status, the United States, United Kingdom, Israel, and Canada reported poliovirus from type 2 vaccines in environmental samples. The United States (Rockland County, New York) also reported one young adult polio case in July 2022 due to vaccine-derived poliovirus type 2 (VDPV).

What Caused Type 2 VDPV Incidents in the United States?

Vaccination range

Vaccination coverage with three routine doses of inactivated polio vaccine (IPV) in the United States was 92% However, vaccination coverage in Rockland County, New York, where young adults contracted poliovirus and developed flaccid weakness of the lower extremities, was very low, at 60.3% as of August 2022, and 37.3% by zip code. August 2022 report in the Weekly reports of morbidity and mortality (MMWR). Most importantly, polio-infected young people were not vaccinated.

A 3-year-old child in Jerusalem, Israel, March 2022 got polio Type 3 by VDPV. Like New York youth, children in Jerusalem were not vaccinated. Type 3 VDPV virus was also detected in six of her asymptomatic children. “Of those seven of her children, one had an incomplete polio vaccination, while six of her others had not,” one says. WHO report.

As long as wild poliovirus exists and all countries continue to use oral polio vaccine (OPV), regardless of the polio situation in the country or which vaccine is in use, the risk of polio outbreaks, including in polio-free countries, is real, especially in globalized villages where vaccine coverage is low. Improving vaccination coverage at national and local levels will help prevent children from contracting polio disease, but complete global eradication will only be possible if wild poliovirus is eradicated and OPV use is stopped.

Type 2 poliovirus is responsible for more than 95% of VDPV cases, and since 1999, when wild poliovirus type 2 was eradicated, all polio cases caused by type 2 virus have been caused by VDPV or vaccine-associated paralytic poliomyelitis (VAPP). Since the global switch from trivalent (including types 1, 2 and 3) OPV to bivalent (including types 1 and 3) OPV in 2016, not a single child in India has been protected with an OPV vaccine against type 2 virus. All prevention is provided exclusively by her IPV including Type 1, Type 2 and Type 3. However, since 2016, India has not reported her single VDPV case of type 2. This further illustrates why India can safely switch to her IPV-only vaccination early.

The need to maintain very high polio vaccination coverage in India cannot be overemphasized, as wild-type and VDPV cases are still being reported in Pakistan and Afghanistan. India has also remained polio-free since January 2011 due to its high polio vaccine coverage, despite reports of wild poliovirus and VDPV cases in Pakistan and Afghanistan. It is mandatory for anyone traveling to India from a polio-endemic country to have her OPV vaccination prior to travel to reduce the risk of spreading the virus in India.

Continued use of bivalent OPV in India carries the risk of emergence of types 1 and 3 VDPV and VAPP cases, creating a need to maintain high polio vaccination coverage in India, even without considering the risk of imported cases. VDPV cases will only occur if enough people are not vaccinated against polio.

Decrease in VAPP incidence

Although wild-type type 2 poliovirus does not exist and is not used in oral vaccines, type 2 VDPV still causes many cases each year, even after the global switch to bivalent OPV in 2016. About 40% of vaccine-associated paralytic poliovirus (VAPP) cases are caused by the type 2 oral polio vaccine. Most of the VDPV and VAPP cases reported in the last two decades have been from countries that continue to use the oral polio vaccine. In contrast, countries that have switched to inactivated polio vaccines remain polio-free (both VDPV and VAPP) except for 2022.

Many developed countries stopped using OPV decades ago and switched to IPV. For example, the United States transitioned to IPV sequentially in his 1997, with both IPV and OPV vaccines used. Rationale: “This strategy aims to reduce the incidence of VAPP while maintaining high levels of herd immunity to poliovirus to prevent poliovirus outbreaks should wild poliovirus be reintroduced into the United States.” (January 1997 document) MMWR report. The risk associated with VAPP when OPV was used was estimated as follows: 30-40 cases Between 1997 and 2000, there were an average of 8 to 10 VAPP cases per year in the United States, but the sequential vaccination schedule was expected to reduce VAPP cases by at least half.

In addition to the risks of causing VDPV and VAPP, India’s OPV, contrary to popular belief, low seroconversion rate It was about 65% for types 1 and 3 and 96% for type 2. Due to the low efficacy of the vaccine, “the number of vaccine-failed polio cases increased with the increase in his trivalent OPV prevalence in India.”

Seroconversion after each booster dose was as frequent as after the first dose. 2016 paper notes was announced in Pediatrics in India. Children in India were still at risk of contracting the poliovirus, even after receiving six doses of the vaccine. Her 10 doses of OPV vaccine were required to achieve the vaccine efficacy of her 3 doses seen in other countries. In most parts of India, transmission of wild poliovirus was prevented only when children received an average of 8-9 doses of OPV.

seroconversion

Children infected with wild poliovirus shed the least amount of virus and for a shorter duration in the event of an OPV challenge compared to children who have never been infected with poliovirus. A child who was vaccinated with OPV and then challenged with OPV shed less virus for a shorter duration than a child who received IPV and was challenged with her OPV.

According to virologist Dr. Jacob John, viral shedding lasts more than 24 hours and continues for weeks in children who were initially given OPV and subsequently infected. “This clearly shows that mucosal immunity is not absolute in the case of OPV,” he says. “Virus shed in stool does not automatically lead to infection.”

The ease of administration of OPV is often cited as a reason for continued use of OPV. However, IPV shortages encouraged countries to opt for split doses of IPV vaccine via intradermal administration prior to the global switch. Since 2016, India has used a split-dose (0.1ml) IPV vaccine administered intradermally at weeks 6 and 14. Administration of intradermal vaccines is more difficult than intramuscular doses. However, India successfully vaccinates millions of children each year with IPV in divided doses. After January 2023a third divided dose of IPV at 9–12 months is included in the national immunization programme.

a judgment was held Indian investigators found that two divided doses of IPV administered intradermally at weeks 6 and 14 and bivalent OPV at birth, weeks 6, 10 and 14 were effective, resulting in >95% seroconversion against poliovirus types 1 and 3 and >85% seroconversion against poliovirus type 2.

OPV is certainly easy to manufacture, and such vaccines are also cheap. Traditionally, IPV was manufactured using wild poliovirus. However, IPV can be produced using an attenuated virus (Sabin IPV). Bharat Biotech, which has a BSL-3 manufacturing facility, was in the early stages of manufacturing the Sabin IPV vaccine in 2020 when the pandemic broke out, and its manufacturing facility was used to produce covacin instead. If Bharat Biotech is licensed to manufacture Sabin IPV, India will no longer need to rely on other countries for its vaccine supply.

Ground to switch

addition of 3rd divided dose An increase in IPV at 9-12 months in a national immunization program further enhances protection against all three types of poliovirus, including both wild poliovirus and VDPV. Given that India has not reported any cases of wild poliovirus or VDPV since it was declared polio-free, and other countries reported VDPV cases during the pandemic, a revised immunization schedule for IPV after nine months could allow India to plan a switch from OPV to IPV once vaccine coverage reaches 85% or more nationwide.

and April 2020 ReportWHO’s Strategic Advisory Group of Immunization Experts (SAGE) urged caution on countries planning to transition from bivalent OPV to IPV-only immunization schedules and recommended that these countries take a “step-by-step approach, first introducing a second dose of IPV into routine immunization”. Seroconversion rates after two doses of IPV at weeks 6 and 14 in Indian children were already 95% for poliovirus types 1 and 3 and >85% for poliovirus type 2. Additional fractionated doses of IPV administered intradermally between 9 and 12 months of age are expected to increase the type 2 seroconversion rate, which is currently only over 85%, in particular.

Similar to the United States in 1997, India also introduced two divided doses of IPV since 2016 and has been poised to switch to a gradual switch to proprietary IPV. Adding a third split dose at 9-12 months is in line with this sequential switch and the recommendation by SAGE. A move to exclusively use his IPV for polio immunization in India could begin once there is very high evidence of seroconversion for all three polioviruses.

All countries that have switched from OPV to IPV consider only the last outbreak of wild poliovirus and VDPV within their borders. India should also adopt such an approach, given the evidence of very high seroconversion after 3 divided doses of IPV and high vaccination coverage achieved using 3 divided doses of IPV.