Postvaccinal encephalitis

Postvaccinal encephalitis (PVE) is postvaccinal complication which was associated with vaccination with vaccinia virus during worldwide smallpox eradication campaign.[1] With mortality ranging between 25 – 30% and life lasting consequences between 16 – 30% it was one of the most severe adverse event associated with this vaccination. The mechanism of its underlying condition is unknown.[2]

Symptoms

PVE symptoms start to appear between 8th and 14th day after vaccination. Amongst first are fever, headache, confusion and nausea. With passing time lethargy, seizures, short and long term memory dysfunctions, localized paralysis, hemiplegia, polyneuritis and convulsions. In extreme cases PVE can lead to coma and death.[3][1]

Treatment

Vaccinia immunoglobulin was given to patients with PVE. But some significant effect of this treatment was observed only if given before PVE developed. That’s why only supportive treatment was given to patients with PVE to attenuate symptoms. Source

Histology

Inflammatory extra-adventitial lesions are found not only in brain but in spinal cord as well. Lesions might be uniform in acute phase or disseminated in subacute phase. Unlike in case of encephalitis lethargica the main damage is found in white brain matter. Meninges are infiltrated with T cell, plasmatic cells and phagocytic cells. Polymorfonuclear cells were found only in severe lesions. Apart from cellular infiltrate in perivascular space there is a tissue rarefication in space close to damaged blood vessels. Accumulated small nuclei are found in places of such rarefication. Strong demyelination with rapid clearance of degraded myelin is also observed in cases of PVE. Tissue damage leads to necrosis in the end.[4]

Incidence

Vaccination with vaccinia virus was accompanied with a whole spectre of adverse events. Some of them were even lethal. Generally accepted number of deaths after vaccination with life vaccine is one per one million vaccinations. But during the eradication campaign more than one vaccination strain was used and these strains differed significantly in causing adverse events.

The incidence of PVE was between 44,9 cases per one million vaccinations with Bern strain used in western Europe to 2,9 cases per one million vaccination with NYCBH strain used in USA. Number of deaths directly connected to PVE also differed from strain to strain. With 11 deaths per one million vaccinations with Bern strain to 1,2 deaths per one million vaccinations with NYCBH strain. PVE incidence also depended on the age of vaccinated person. That’s why in USA children up to one year of age and in Europe children up to three years of age were excluded from vaccination.[5]

History

Complications with central neural system after smallpox vaccination were observed for the first time right after the vaccination begun. The first diagnosed case of PVE was in 1905.[3]

In times of smallpox eradication campaign, when PVE was a serious problem, there were no tools for identification of immune mechanism behind PVE available. And considering the fact that nowadays smallpox vaccines are much safer and only chosen personnel gets vaccinated, PVE is no longer in centre of attention. Nevertheless, for its similarity with acute disseminated encephalomyelitis (ADEM), which is also postvaccinal adverse reaction (observed for example after anti hepatitis A or B virus vaccination), PVE is considered to be of autoimmune nature. There is no final proof of PVE being caused directly by vaccine virus replication in neural tissues.[6]

References

  1. 1 2 Jorge, Ricardo (January 1932). "POST-VACCINAL ENCEPHALITIS : ITS ASSOCIATION WITH VACCINATION AND WITH POST-INFECTIOUS AND ACUTE DISSEMINATED ENCEPHALITIS". The Lancet. 219 (5656): 215–220. doi:10.1016/S0140-6736(00)82942-6.
  2. ↑ "Post-Vaccination Encephalitis". Annals of Internal Medicine. 5 (3): 333. 1 September 1931. doi:10.7326/0003-4819-5-3-333.
  3. 1 2 Roos, K L; Eckerman, N L (2002). "The smallpox vaccine and postvaccinal encephalitis". Semin Neurol. 22 (1): 95–98. doi:10.1055/s-2002-33052.
  4. ↑ Perdrau, J R (1928). "The histology of post‐vaccinal encephalitis". The Journal of Pathology. 31: 17–39. doi:10.1002/path.1700310104.
  5. ↑ Kretzschmar, Mirjam; Wallinga, Jacco; Teunis, Peter; Xing, Shuqin; Mikolajczyk, Rafael (2006). "Frequency of Adverse Events after Vaccination with Different Vaccinia Strains". PLoS Med. 3 (8): 1341–1351. doi:10.1371/journal.pmed.0030272.
  6. ↑ Rogalewski, Andreas; Kraus, Jörg; Hasselblatt, Martin; Kraemer, Christoffer; Schäbitz, Wolf-Rüdiger (2007). "Improvement of advanced postvaccinal demyelinating encephalitis due to plasmapheresis". Neuropsychiatric Disease and Treatment. 3 (6): 987–991.
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