This article is a response to ‘The case for the oral polio vaccine in the world’s quest for eradication’, July 21, 2023, by Vipin M. Vashishtha and Puneet Kumar.
In 2022, after greater than a decade of remaining polio-free, the U.S., the U.Ok, Israel and Canada reported kind 2 vaccine-derived poliovirus in environmental samples. The U.S. (Rockland County in New York) additionally reported one case of polio in a younger grownup brought on by kind 2 vaccine-derived poliovirus (VDPV) in July 2022.
What prompted the kind 2 VDPV case to emerge in the U.S.?
Vaccine protection
Vaccine protection with three routine doses of inactivated polio vaccine (IPV) in the U.S. was 92% in 2021. However, vaccine protection in Rockland County in New York, the place the younger grownup was contaminated by poliovirus and developed flaccid decrease limb weak point, was very low — 60.3% in August 2022, and the zip code-specific protection was as little as 37.3% — in accordance to an August 2022 report in the Morbidity and Mortality Weekly Report (MMWR). Most importantly, the younger grownup who obtained polio was unvaccinated.
In March 2022, a three-year-old little one in Jerusalem metropolis, Israel developed polio due to kind 3 VDPV. Like the younger grownup in New York, the little one in Jerusalem metropolis was not vaccinated. The kind 3 VDPV virus was detected in six extra youngsters who have been asymptomatic. “Of these seven children, one had incomplete polio immunisation while the other six were unvaccinated,” says a WHO report.
No matter the polio standing of a rustic and which vaccine is getting used, so long as wild poliovirus is current and any nation continues to use the oral polio vaccine (OPV), the threat of polio emergence, together with in polio-free international locations, is actual in a globalised village particularly when vaccine protection is low. While rising vaccination protection nationally and at a group degree will assist forestall youngsters from getting polio illness, full eradication from the world will turn into attainable solely when wild polioviruses are worn out and the use of OPV is stopped.
Type 2 poliovirus has been accountable for over 95% of VDPV instances, and since 1999, when wild poliovirus kind 2 was eradicated, all polio instances brought on by kind 2 virus have been both due to VDPV or vaccine-associated paralytic poliomyelitis (VAPP). Since the international change from trivalent (containing sorts 1, 2, and three) to bivalent (containing sorts 1 and three) OPV in 2016, no little one in India has been vaccine-protected with OPV towards kind 2 virus. All the safety has come solely from IPV, which comprises sorts 1, 2 and three. Yet not a single kind 2 VDPV case in India has been reported since 2016. This additional demonstrates why India can safely change to exclusive-IPV immunisation at the earliest.
Since wild and VDPV instances are nonetheless reported in Pakistan and Afghanistan, the compulsion to preserve a really excessive polio vaccine protection in India can’t be overemphasised. Also, India has remained polio-free since January 2011 at the same time as wild poliovirus and VDPV instances have been reported in Pakistan and Afghanistan, thanks to excessive polio vaccine protection right here. Any particular person travelling to India from a polio-endemic nation is required to get immunised with a dose of OPV prior to journey, to cut back the threat of spreading the virus right here.
The want to preserve excessive polio vaccine protection in India arises even with out contemplating the threat of imported instances, as continued use of bivalent OPV in India carries the threat of kind 1 and sort 3 VDPV and VAPP instances rising. VDPV instances can emerge solely when sufficient individuals are not vaccinated towards polio.
Decreasing VAPP incidence
Despite wild kind 2 poliovirus being non-existent and never utilized in oral vaccines, kind 2 VDPV has prompted many instances annually even after the international change to bivalent OPV in 2016. Nearly 40% of vaccine-associated paralytic poliomyelitis (VAPP) are brought on by kind 2 oral polio vaccine. Almost all VDPV and VAPP instances have been reported in the final twenty years are from international locations that proceed utilizing oral polio vaccine. In distinction, international locations that switched to inactivated polio vaccine have remained polio-free (each VDPV and VAPP), besides in 2022.
Many developed international locations discontinued OPV use and converted to IPV a couple of a long time in the past. The U.S., for instance, moved to IPV in a sequential method in 1997 the place each IPV and OPV vaccines have been used. The rationale: “This strategy was intended to decrease the incidence of VAPP while maintaining high levels of population immunity to polioviruses to prevent poliomyelitis outbreaks should wild poliovirus be reintroduced to the U.S.,” as per a January 1997 MMWR report. The threat related to VAPP if OPV was used was estimated to be 30-40 instances throughout 1997-2000 (a mean of 8-10 VAPP instances per 12 months) in the U.S., whereas the sequential vaccination schedule was anticipated to cut back VAPP instances by at the very least half.
In addition to the threat of inflicting VDPV and VAPP, the OPV in India, opposite to fashionable notion, was discovered to have low seroconversion charges for sorts 1 and three — about 65% — and 96% for kind 2. Low vaccine efficacy resulted in “increasing numbers of vaccine-failure polio as trivalent OPV coverage increased in India”.
Seroconversion after every further dose was at the identical frequency as after the first dose, notes a 2016 paper revealed in Indian Pediatrics. Children in India, even after receiving half-a-dozen doses, have been nonetheless vulnerable to getting contaminated by poliovirus. As many as 10 doses of OPV vaccine have been required to attain a three-dose vaccine efficacy seen in different international locations. Wild poliovirus transmission was interrupted in most components of India solely when a mean of eight-nine OPV doses got to a baby.
Seroconversion
Compared with poliovirus-naïve youngsters, these contaminated with wild poliovirus shed the least quantity of virus and for a shorter length when challenged with OPV. Children vaccinated with OPV after which challenged with OPV shed a lesser quantity of virus and for a shorter length than these given IPV and challenged with OPV.
According to virologist Dr. Jacob John, virus shedding goes on past 24 hours and continues for a couple of weeks even in youngsters initially given OPV after which challenged. “This clearly demonstrates that mucosal immunity is not absolute in the case of OPV,” he says. “Virus shedding in the stools does not automatically translate into transmission.”
The ease of administering OPV is commonly cited as a purpose for persevering with the use of OPV. But due to scarcity of IPV, international locations have been inspired to decide for a fractional dose of IPV vaccine administered intradermally prior to the international change. India has been utilizing a fractional dose (0.1 ml) of IPV vaccine administered intradermally at 6 and 14 weeks since 2016. Administering an intradermal vaccine is more difficult than an intramuscular dose. Yet India has been efficiently immunising thousands and thousands of kids annually with fractional IPV doses. Since January 2023, a 3rd fractional dose of IPV at 9-12 months has been included in the nationwide immunisation programme.
A trial carried out in India discovered that two fractional doses of IPV administered intradermally at six and 14 weeks adopted by bivalent OPV at beginning, and age six, 10, and 14 weeks is efficient and gives over 95% seroconversion towards poliovirus sorts 1 and three and over 85% seroconversion towards kind 2 poliovirus.
Manufacturing OPV is certainly straightforward and such vaccines are additionally low-cost. Traditionally, IPV was manufactured utilizing wild polioviruses. But IPV could be manufactured utilizing the attenuated viruses (Sabin IPV). Bharat Biotech, which has a BSL-3 manufacturing facility, was at an early stage of producing Sabin IPV vaccines in 2020 when the pandemic struck and the manufacturing facility was as a substitute used to produce Covaxin. When Bharat Biotech is licensed to manufacture Sabin IPV, India will now not want to depend on different international locations for vaccine provide.
Ground to change
The addition of a third fractional dose of IPV at 9-12 months in the nationwide immunisation programme will additional enhance the safety towards all three varieties of polioviruses, each wild and VDPV. Considering that India has not reported any case of untamed poliovirus or VDPV because it was licensed polio-free and even when different international locations reported VDPV instances throughout the pandemic, India can plan to make a change from OPV to IPV as soon as the vaccine protection reaches over 85% throughout the nation with the revised immunisation schedule of IPV at 9 months.
In an April 2020 report, WHO’s Strategic Advisory Group of Experts on Immunization (SAGE) needed international locations planning to transfer from bivalent OPV to IPV-only immunisation schedule to train warning and beneficial that these international locations ought to as a substitute take a “gradual approach, first introducing a second dose of IPV into routine immunisation”. Seroconversion after two fractional doses of IPV given at six and 14 weeks in Indian youngsters was already 95% towards poliovirus kind 1 and sort 3 and over 85% towards kind 2 poliovirus. The further fractional dose of IPV given intradermally at 9-12 months is anticipated to enhance the seroconversion, significantly for kind 2, which is presently solely over 85%.
Like the U.S. in 1997, India has made floor to change over to unique IPV in a sequential method since 2016 with the introduction of two fractional doses of IPV. The addition of a 3rd fractional dose at 9-12 months is in keeping with this sequential change and the suggestion by SAGE. The transfer to unique use of IPV for polio immunisation in India can start as soon as we have now the proof for very excessive seroconversion for all three varieties of polioviruses.
All international locations which have made a change from OPV to IPV have solely thought-about the final occasion of untamed poliovirus and VDPV instances inside their borders. India too ought to undertake such an strategy and after proof of very excessive seroconversion after three fractional doses of IPV and as soon as excessive vaccine protection has been achieved utilizing three fractional IPV doses.
