But as the wild-type polio virus, serotype 2, disappeared completely exterminated in 2015, serotype 3 – in 2019 – the comparative number of cases of vaccine-associated poliomyelitis began exceed the number of cases of disease caused by a wild virus, the foci of which have survived only in Afghanistan and Pakistan. In order to eliminate the risks of disease caused by the modified virus from live vaccines, developed countries have decided to completely abandon them and switch only to OPV. Since the early 2000s, a significant proportion of rich countries have switched to vaccination with only inactivated vaccine. But most of the world still using the combined scheme (first IPV, then OPV), and although in 2016 the second serotype of poliovirus, which caused up to 94% of all cases of vaccine-associated poliomyelitis, was almost universally excluded from live vaccines, cases of illness and paralysis due to infection with the vaccine virus continue to be detected. Since 2017, there have been 396 cases of wild virus-associated polio and over 2,600 cases of disease associated with the virus from live vaccines.
Poor countries cannot stop using live polio vaccine primarily for financial and logistical reasons. OPV is much cheaper than IPV, and it is not only healthcare workers who can vaccinate children with it. In addition, during the transition period, countries may need stocks of live vaccines containing only one serotype of poliovirus in order to control possible outbreaks of vaccine-associated poliomyelitis. Theoretically, the WHO could contribute to the universal transition to IPV, but, as it became especially obvious in covid, its ability to influence the policy of states is very limited.
Man-made potential epidemic
As a result, people vaccinated with OPV, vaccinated with IPV and unvaccinated people live side by side in the world today. This combination, given the growing number of non-immune children and the possibility of reaching the other side of the planet in a few hours, creates excellent conditions for the spread of a modified virus from live vaccines. An example scenario is as follows: a child who has recently received a dose of a live vaccine, and therefore is actively shedding attenuated polioviruses in feces, flies from a country where OPV is actively used, say, to the States where this vaccine has not been used since 2000. That is, all young Americans who have already received only IPV – or who have not been vaccinated at all – can serve as passive distributors of vaccine viruses. Transmitted from person to person, such viruses can acquire the very changes that they need to restore pathogenicity. When such a virus enters the body of an unvaccinated person, it can cause symptomatic illness that is clinically indistinguishable from wild-type polio.
And this is what apparently happened in New York City, where a young unvaccinated man developed paralysis in the Rockland County area. The Orthodox Jewish community lives there compactly, the level of vaccination against polio in which is about 37%. The virus that caused paralysis belongs to the second serotype of vaccine viruses, but on the way from the vaccine to the sick person, it acquired about 10 mutations. An analysis of wastewater in New York City found exactly the same virus, and comparing its genome with the genomes of polioviruses found earlier this year in sewage from London and Jerusalem, showedthat these pathogens are related to each other. The New York case had not traveled to areas where he might have been exposed to poliovirus shortly before the onset of symptoms, suggesting that he was infected by one of the vaccine virus type 2 transmitters, either vaccinated with IPV or unvaccinated, who left the virus behind. footprint in wastewater. Who and when brought the virus to New York is unknown, but it is clear that this person was somehow part of the “silent” infection chains associated with London and Jerusalem.
And this is not the first case of such chains. In March 2022, a three-year-old girl who had not been vaccinated against polio developed paralysis in Jerusalem in Jerusalem, analysis of samples showedthat it was caused by a virus from the Sabin type 3 vaccine. It was distinguished from the original virus by 17 mutations. Relatives of this virus were previously found in the wastewater of Jerusalem and Bethlehem, that is, in this case, we can talk not about accidental infection, but about long-term circulation and changes in the original vaccine virus. By April 15, doctors found six more children (later two more) infected with the same poliovirus. Five were unvaccinated, one child was partially vaccinated.
It can be assumed that the actual spread of circulating polioviruses from live vaccines is much wider. Analysis of wastewater for pathogens is labor intensive and is not routinely performed in many regions. Sporadic measurements discovered polioviruses from live vaccines in London (although wastewater is regularly examined there) and New York, and even two different variants were found in Israel. Probably, if you study sewage flows systematically, you can learn a lot of interesting things about other regions.
Latent circulation of vaccine-associated polioviruses poses a danger primarily to non-immune ones. After vaccines rid humanity of many deadly pathogens that used to claim hundreds of thousands of children’s lives, vaccine skepticism began to systematically grow. An additional sharp failure in vaccination has occurred due to coronavirus restrictions, and today the number of children vulnerable to viruses and bacteria that are not completely eradicated is especially large. In response to cases of paralysis caused by poliovirus in Israel and London deployed emergency vaccination campaigns for all non-immune children – however, vaccination was not mandatory, and parents were only asked to vaccinate their children.
But in order to solve the problem globally, it is necessary to stop the use of OPV throughout the world, in parallel with the vaccination of all unvaccinated IPV. Without this, “escaped” vaccine strains will continue to circulate, periodically regaining their pathogenicity. Theoretically, this option looks like a workable one, but in practice, the likelihood of a centralized replacement of OPV with IPV in poor countries is close to zero – suffice it to recall the complete failure of the Covax campaign to supply countries in need with coronavirus vaccines. For example, in Africa at the beginning of July 2022, a full course of vaccination against coronavirus passed 21.1% percent of the population, and in many states of the continent the proportion of those vaccinated did not even reach 10%.
Another option is to replace the second serotype of poliovirus in live vaccines (it changes more often than others and causes most cases of vaccine-associated poliomyelitis) with a more genetically stable one. OPV containing such an altered strain, received permission for emergency use in 2020, but so far its mass distribution has not occurred. Perhaps cases of paralysis caused by poliovirus from vaccines in developed countries will spur efforts to introduce it. If the situation remains as it is, we should expect an ever-widening spread of the virus from live vaccines and new diseases, paralysis and death.