Since this emergency committee on Zika virus first met on 1 February, substantial new clinical and epidemiological research has strengthened the association between Zika infection and the occurrence of fetal malformations and neurological disorders.
In addition, the geographical distribution of the disease is wider. The risk group is broader. And the modes of transmission now include sexual intercourse as well as mosquito bites.
Local transmission has now been reported in 31 countries and territories in Latin America and the Caribbean.
In this region, cases of dengue, which is carried by the same mosquito species as Zika, typically increase during the rainy season, which lasts from January to May. We can expect to see more cases and further geographical spread.
Imported cases of Zika have been reported from every region in the world.
Concerning the link with fetal malformations, the virus has been detected in amniotic fluid. Evidence shows it can cross the placental barrier and infect the fetus. We can now conclude that Zika virus is neurotropic, preferentially affecting tissues in the brain and brain stem of the developing fetus.
Zika has been detected in the blood, brain tissue, and cerebrospinal fluid of foetuses following miscarriage, stillbirth, or termination of pregnancy.
Microcephaly is now only one of several documented birth abnormalities associated with Zika infection during pregnancy. Grave outcomes include fetal death, placental insufficiency, fetal growth retardation, and injury to the central nervous system.
To date, microcephaly has been documented in only two countries: French Polynesia and Brazil. However, intense surveillance for fetal abnormalities is currently under way in countries, like Colombia, where the outbreaks started later than in Brazil.
Nine countries are now reporting an increased incidence of Guillain-Barré syndrome or laboratory confirmation of a Zika virus infection among GBS cases. A retrospective case-control study of GBS associated with Zika in French Polynesia recorded no deaths, but the disease progressed rapidly and a large percentage of patients required admission to an intensive care unit for as long as 51 days.
Growing evidence of a link with GBS expands the group at risk of complications well beyond women of child-bearing age. GBS has been detected in children and adolescents but is more common in older adults and slightly more common in men. The anticipated need for expanded intensive care adds a further burden on health systems.
Reports and investigations from several countries strongly suggest that sexual transmission of the virus is more common than previously assumed.
All of this news is alarming.
Women who are pregnant in affected countries or travel to these countries are understandably deeply worried.
I convened this second meeting of the Emergency Committee to gather expert advice on the strength and significance of these new research results. We also asked the experts whether the findings warrant changes in WHO recommendations to countries.
The Committee underscored the increasing strength of evidence showing a likely association between Zika infection and fetal malformations and neurological disorders.
At the same time, the experts pinpointed the types of studies needed to establish a causal relationship, but stressed their view that strong public health actions should not wait for definitive scientific proof.