New Delhi: On May 24, two days before the World Health Organization (WHO) announced that India has had three positive cases of Zika virus (ZIKV), the global body put India in category 2 in WHO’s country classification scheme. This category indicates that India is now an area “with ongoing transmission” of ZIKV.
In April, India was in category 4, which is the bottom-most category of countries in WHO’s classification, implying that these countries have the least risk of ZIKV transmission. India now joins Brazil in category 2. Brazil was the centre of the 2015 Zika epidemic that swept large parts of South and North America.
In WHO’s disease outbreak news on India on May 26, the organisation did a risk assessment and said that their findings “suggest low level transmission of Zika virus and new cases may occur in the future.” WHO also said, “The risk of further spread of Zika virus to areas where the competent vectors, the Aedes mosquitoes, are present is significant given the wide geographical distribution of these mosquitoes in various regions of the world.” However, WHO did not recommend any travel or trade restrictions to India.
The health ministry finally put out a press release on the issue late Thursday night. This comes a whole week after WHO put India in a higher-risk category. Their press release is silent on this update. The government says, “No other sample has been tested positive apart from the three laboratory confirmed cases reported from Ahmedabad.” It also says, “Since WHO had already withdrawn the notification of Zika virus disease as a PHEIC [public health emergency of international concern], the case was handled as per our existing protocol.” The Wire had earlier reported that WHO has clarified that all countries need to notify the WHO of diseases like Zika, even if they are not classified as a PHEIC.
What is the ZIKV classification of countries?
The WHO classifies 148 countries regularly, based on four different transmissions of the ZIKV. These are the four different categories which WHO maintains, and groups countries accordingly. This is a dynamic classification table of countries and regions, giving their risk level at the time. This classification changes as surveillance data brings in new information. The transmission of ZIKV depends on the presence of the vector and also climatic conditions. ZIKV’s distribution might overlap with the locations of previous or current dengue outbreaks. Countries in category 1 need and will receive the most urgent attention.
WHO’s recent classification of India as category 2 means India is an “area with ongoing transmission” of ZIKV. In this regard, it is similar to the highest alert category, which is category 1, but it differs from category 1 countries as here, the virus is not considered to be new or recently re-introduced, but could have been in circulation before 2015.
In April, India was in category 4, along with 63 other countries. In the Southeast Asia region, this included Bhutan, Myanmar, Nepal, Sri Lanka and Timor-Leste, besides 33 countries in WHO’s African region. Countries in category 4 are those that have the established vector (Aedes aegypti), but have not had any documented cases or current cases of transmission of ZIKV infection. If laboratory confirmed cases of autochthonous vectorborne case of ZIKV infection are detected, then WHO says this may indicate a situation of previously unknown and undetected transmission, which would put countries in category 1 and these countries “will be reclassified accordingly”. This seems to be what has happened with India.