(English) Zika: The key unanswered questions

 This grainy image is one of the few pictures of the Zika virus.

The infection has prompted the World Health Organization to declared a global health emergency due to the link to thousands of suspected cases of babies born with small brains – or microcephaly – in Brazil.

But there are still many, crucial, unanswered questions.

 How many people have been infected in the Americas?

The best estimate of Zika infections is between 500,000 and 1.5 million – which is quite a wide margin of error. What percentage of people in an affected area are getting infected? Is it everyone? We don’t know.

 Why the explosive outbreak?

One theory is that the virus has mutated to become more infectious. Alternatively, some experts argue it could simply be a case of the virus reaching areas where people are densely packed together and there are huge numbers of mosquitoes.

 Who is infectious?

Around 80% of people have no symptoms when they get the virus – although this figure needs further investigation. It’s not known if they can also spread the virus or even why they are asymptomatic.

 Does it cause microcephaly?

It’s the biggest health concern in the outbreak, yet the link with Zika and birth defects is still only “strongly suspected”. Parts of Brazil that have seen cases of Zika have, several months later, also seen a surge in microcephaly. However, the trials to prove the link have not finished.

 How risky is infection?

If the virus does cause microcephaly, how often does this happen? Does every infection lead to birth defects? Or is it one-in-100? One-in-10,000 perhaps? At the moment it’s not clear how worried pregnant women should be.

 What about immunity?

Are you infected once and then protected for life, like measles? Or does it take multiple infections to achieve immunity? How long does immunity last? These answers will tell us how long the outbreak could last and indicate whether a vaccine would be effective.