The US Centers for Disease Control and Prevention (CDC) reported that there were about 4,000 confirmed cases of Zika in the US and 1,300 deaths, compared to about 300 cases in Europe.
The WHO reported a similar number of confirmed and probable cases.
The UK’s Department for Environment, Food and Rural Affairs (DEFRA) said there were 1,800 confirmed cases and 2,500 deaths.
There was also some speculation that there might be as many as two new cases a day, although experts said that would be very unlikely.
Dr John Mearsheimer, an expert in infectious diseases at New York University School of Medicine, told ABC News that there was a lot of scepticism around the potential impact of Zika on the global health community.
“It is going to be very difficult to know what will happen to the rest of the world,” he said.
“[The WHO] did a pretty thorough review of the literature on the virus, and I would put that at a level of the most conservative of any public health body, and that is that we don’t really know.
It is quite clear that we are going to have a lot more work to do, but it will not be a problem.”
Dr Mearsheim added that there could be cases of people infected with the virus who don’t have any symptoms and that this could affect the quality of care they receive.
A spokesman for DEFRA said: “We take our role in protecting people’s health very seriously, and we do not believe that the public is in danger from Zika.”
Health workers have been trying to limit the spread of the virus to reduce the risk of people contracting the disease from other people.
The WHO reported that health workers have reported a higher number of infections than the general population, but warned that it could be much higher.
Zika is transmitted by the Aedes aegypti mosquito, which is transmitted through blood, saliva and sweat.
The virus has been found in the blood of many of the 1.3 million people in the Americas.
WHO said the virus could spread to the eyes and nasal cavities of people who have travelled to areas with active transmission.
If there is no response from the WHO, it will continue to spread.
While the virus has not been linked to any outbreaks of microcephaly, in which babies are born with abnormally small heads, Dr Mearsmeier said there was some concern about its effects on developing brains.
He said: “We are just starting to understand how this will affect brain development.
It could impact people’s mental health as well.”
The UK government said it had already set up an emergency centre in Cardiff to support health workers, and has also set up a Zika education and research network.