The authorities in the Netherlands have detected a leak of a wild type of the polio virus already eradicated in a vaccine factory located near Utrecht, in the central zone of the country. The episode has affected a worker at the facilities, who was vaccinated and has had the infection asymptomatically. For security reasons, this employee had to remain in isolation in special facilities from December 8 to January 11, since he excreted the virus through…
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The authorities in the Netherlands have detected a leak of a wild type of the polio virus already eradicated in a vaccine factory located near Utrecht, in the central zone of the country. The episode has affected a worker at the facilities, who was vaccinated and has had the infection asymptomatically. For security reasons, this employee had to remain in isolation in special facilities from December 8 to January 11, since he excreted the virus through his feces.
The investigations opened after the alarm decreed by the country’s authorities have not detected more infections. The event has been dealt with in the meeting held on January 25 of the World Health Organization (WHO) Emergency Committee and the Research results have been published in the latest issue of the journal Eurosurveillance from the European Center for Disease Control and Prevention (ECDC).
This is the most serious incident of these characteristics that has occurred in decades in the European Union. The last similar one that has been published happened in 2014 in Belgium, when a human error in a GlaxoSmithKline (GSK) pharmaceutical facility released 45 liters of a solution with live polio virus into the environment. On that occasion, however, no person was infected and the authorities established that there was no risk to the population.
All alerts were raised in early December after the virus was detected in routine surveillance tests carried out by the Netherlands National Polio Laboratory on wastewater collected on November 15. These safety tests are regularly carried out every three weeks in facilities considered essential, such as those dedicated to the production of vaccines and diagnostic laboratories, with the aim of detecting any leaks. The virus was detected in a sample taken at the company Bilthoven Biologicals (BBio). The company has reported that it has “paralyzed all activities with active poliovirus” until the causes of the incident “are fully clarified and all processes have been reviewed.”
The form of the virus implicated has been a wild type 3 strain (WPV3-Saukett G), last detected naturally in Nigeria and declared eradicated by the WHO in October 2019. Of the three types of wild poliovirus, only 1 continues to cause cases in the world. It is endemic to Pakistan and Afghanistan, although a year ago it was also detected in Malawi. Type 2 was also declared eradicated, in 2015, after being last diagnosed in India in 1999.
Following the detection of the pathogen in wastewater, the Dutch authorities launched an investigation into all company employees who had had access in the previous three weeks to work areas where the virus is handled, 51 people in total. . Two stool samples and one serum were taken from each one, and one of them tested positive.
“The infected worker agreed to voluntary isolation under the daily supervision of the local public health service,” according to published research. As this employee lived in an area of the Netherlands “with suboptimal vaccination coverage” among the population, less than 90%, and there was a risk that the virus would spread and could cause serious cases of polio, compliance with isolation was ruled out. at home and was accommodated in a residence provided by the authorities “designed for the isolation of employees and located in an area with vaccination coverage greater than 90%.”
During the isolation, the affected worker was not allowed “to receive guests, but could walk, exercise and meet people outside as long as they did not have any physical contact with them.” “After 33 days, the employee was released from isolation on January 11, 2023, after three consecutive negative stool samples,” the investigation states.
The country’s authorities also carried out meticulous contact tracing of the worker’s contacts in the days prior to the identification of the virus. 16 co-workers and 11 private contacts were identified, who were analyzed with a total of 54 samples studied (two per person). They all tested negative.
security breach
The researchers have concluded that the vaccine factory facilities suffered a “failure” in security measures that required a rapid response from the authorities to prevent the spread of the virus among the population. The findings published in Eurosurveillance highlight the importance of “environmental surveillance” measures through wastewater from facilities considered sensitive for working with active strains of the virus, since “incidents that lead to a leak and even an infection may go unnoticed”.
Polio viruses are extremely contagious and are spread by contact with an infected person. Most infections are asymptomatic, but about a quarter will develop flu-like symptoms (fever, tiredness, aches…). In the most serious cases, up to 5% of those infected can develop meningitis and paralysis. In these cases, the patient loses muscle strength in the arms or legs until they lose the ability to move them. According to various studies, between 2% and 10% of those who suffer from these more severe forms die because the virus affects the muscles involved in breathing.
The vaccines used in countries that have already managed to eradicate polio are the so-called Salk, which use killed or inactivated viruses. They are injectable and protect against all severe forms of polio because they prevent the infection from reaching the blood and neurons, but they do not confer immunity in the mucous membranes of the digestive system, where the virus can replicate and is excreted in the feces. This means, as in this case, that people vaccinated with these sera can be carriers of the virus and spread the disease to others. Their use is justified in countries where the risk of pathogen circulation is considered low because they have fewer side effects than the other available vaccine, which is administered orally.
This type of immunization, called Sabin, is used in countries still affected by polio or where the risk of circulation is considered high. This vaccine, which uses attenuated viruses, also immunizes at the intestinal level and is the one that has made it possible to eradicate the disease in a large part of the world, since if it is administered universally it ends up cutting off the circulation of the virus among the population. But it also has drawbacks. In some cases, attenuated viruses cause significant adverse effects in the patient, and viruses excreted in feces after vaccination may continue to circulate if unvaccinated population groups remain. In these situations, the pathogen may regain the ability to produce severe cases of the disease, leading to outbreaks of vaccine-derived forms of the virus.
The change in a country from the initial use of the Sabin to the Salk vaccine when the circulation of the virus has been eliminated is a key moment in vaccination strategies against polio throughout the world. Spain took this step in 2004.
