Poliomyelitis


– Poliomyelitis is an acute viral infection due to a poliovirus (serotypes 1, 2 or 3). Human-to-human transmission is direct (faecal-oral) or indirect (ingestion of food and water contaminated by stool). Humans are the only reservoir of the virus. In principle the disease can be eradicated by mass vaccination.
– In endemic areas, poliomyelitis mainly affect children under 5 years not (or not fully) vaccinated, but the infection can affect persons of any age, especially in areas where population immunity is low.

Clinical features

– Up to 90% of cases are asymptomatic or present mild symptoms1.
Non-paralytic form: a non-specific febrile illness with muscle pain, headache, vomiting, backache; no neurological involvement. As spontaneous recovery usually occurs within 10 days, diagnosis is rarely made outside epidemic contexts.

Paralytic form: in less than 1% of cases, after the non-specific signs, the patient develops rapid onset (from the morning to the evening) asymmetrical acute flaccid paralysis, predominantly of the lower limbs, with ascending progression. The muscles become soft with diminished reflexes. Sensation is maintained. The disease is life threatening if paralysis involves the respiratory muscles or muscles of swallowing. Initial urinary retention is common. Gastrointestinal disturbances (nausea, vomiting, diarrhoea), muscle pain and meningeal symptoms may also occur.

Laboratory

Look for the polio virus in stool samples. The virus is excreted for one month after infection, but only intermittently; therefore, 2 samples must be collected with an interval of 24-48 hours, and within 14 days of onset of symptoms2. Send the stool samples to a reference laboratory, with a clinical description of the patient. The stool samples must be stored and transported between 0 °C and 8 °C.

Treatment

– Hospitalise patients with the paralytic form: rest, prevent bed sores in bedridden patients, give analgesics (do not give IM injections to patients in the febrile phase), ventilate patients with respiratory paralysis.
– Physiotherapy once the lesions are stable to prevent muscle atrophy and contractures.
– Care for sequelae: physiotherapy, surgery and prosthetics.

Outbreak control in case of acute flaccid paralysis (AFP)

– Consider any patient with AFP as a suspected case of poliomyelitis.
– Send stool samples to a reference laboratory to confirm the diagnosis.  

– Organize vaccination of all children under 5 years living in the area (from the same village or neighbouring villages) irrespective of their vaccination status, within 14 days of laboratory confirmation and with the available vaccine (round 0)3.
– Organize two mass vaccination campaigns within 8 weeks of the laboratory confirmation. The type of vaccine, the area and the age groups are determined by epidemiological data.
– Organize a mop-up (dor-to-door) vaccination campaign wherever monitoring suggests that children have been missed, to ensure interruption of transmission.
– Surveillance: for each case of AFP there are between 100 and 200 subclinical cases. Therefore, active surveillance to detect new cases is essential for epidemic control.

Prevention

– 3 types of vaccines exist:
• a trivalent injectable inactivated poliovirus vaccine (IPV),
• a bivalent oral live attenuated poliovirus vaccine (bOPV), containing serotypes 1 and 3,
• a monovalent oral type 2 vaccine (mOPV or nOPV) exclusively used for responding to epidemics.
– Vaccination schedule: depends on the epidemiology of the virus.
Protocols vary according to the country, follow national recommendations. For information, the WHO recommends:


Schedule
Primary vaccination

Endemic or at risk zones*

Other zones

Birth

1 dose bOPV**

6 weeks

1 dose bOPV

1 dose bOPV

10 weeks

1 dose bOPV

1 dose bOPV

14 weeks

1 dose bOPV + 1 dose IPV

1 dose bOPV + 1 dose IPV

* Countries where poliomyelitis is endemic or zones at high risk of importation and subsequent spread of the virus.
** The first dose of bOPV is administered at birth, or as soon as possible, to optimise seroconversion rates after subsequent doses and induce mucosal protection.

In children who start routine vaccination late (after the age of 3 months), the dose of IPV is administered together with the first dose of bOPV, followed by 2 doses of bOPV alone administered 4 weeks apart.
There is also an ‘IPV only’ schedule: 3 doses administered at least 4 weeks apart (e.g. at 6, 10 and 14 weeks) and a booster dose at least 6 months later.
IPV should eventually completely replace bOPV.



References

  1. World Health Organization. Poliomyelitis (polio).
    https://www.who.int/health-topics/poliomyelitis#tab=tab_1 [Accessed 08 June 2021]


  2. Centers for Disease Control and Prevention. Poliomyelitis. 2020.
    https://www.cdc.gov/vaccines/pubs/pinkbook/polio.html [Accessed 08 June 2021]

  3. Global Polio Eradication Initiative. Standard operating procedures: responding to a poliovirus event or outbreak, version 3.1. World Health Organization. 2020.
    https://www.who.int/publications/i/item/9789240002999 [Accessed 08 June 2021]