The World Health Organisation has declared that the Zika virus no longer constitutes a public health emergency of international concern. This brings to an end the heightened global focus on the virus that has caused about 2,300 confirmed cases of microcephaly (a birth defect manifesting in a smaller head size) since May 2015. The WHO had declared the Zika virus a public health emergency on February 1, considering the high number of neurological disorders reported in Brazil and a similar cluster in French Polynesia in 2014. Among the reasons cited were the unknown causal link between the virus and microcephaly and neurological complications, the possibility of its global spread, lack of vaccines and diagnostic tools, and the lack of immunity to the virus in newly affected countries. The link between Zika and microcephaly was established in May, the hunt for a potent vaccine and reliable diagnostic tool has begun, and scientists have been able to find the routes of transmission. However, the global risk assessment has not changed. The spread of Zika to 67 countries and territories is a grim reminder of the lack of immunity against the virus and the abundance of mosquito vectors. A dozen countries have reported local transmission.
Despite the link between the Zika virus infection and microcephaly being well established, the entire spectrum of challenges posed by the disease is not known. The WHO Emergency Committee has called for sustained research and dedicated resources to address the long-term challenges posed by babies born with microcephaly, but signalling the end of the global emergency may lead to lowering of the global alert. There should be no setback to funding, the global search for effective vaccines and diagnostic tests, and creating awareness about the risk of sexual transmission. For instance, it is not clear why more babies were born with microcephaly in northeast Brazil compared to the rest of the country or why the country had a higher caseload than others. This information is crucial to understanding the link between Zika infection and microcephaly, and thereby to containing incidence where the mosquito vector is predominant. Medical journals should continue to provide free and immediate access to papers on the Zika virus, which played a crucial role in information-sharing. The WHO has said it is “not downgrading the importance of Zika” and that its “response is here to stay”. It now needs to ensure that vigilance remains high despite the decline in incidence.