Researchers at Antwerp University examined blood taken from 3,600 people of all ages. The results reveal what share of the population had been infected with the virus just before Belgium introduced its lockdown light on 18 March. The samples were taken three weeks ago, but immunity takes a further two weeks to appear in your blood putting back the date for which they give a picture to around 15 March.

The samples were taken from people who consulted their doctor for a range of concerns not immediately linked to the corona crisis. Samples were processed anonymously.

A 3% infection rate means that in Belgium herd immunity is still very far off. Scientists had expected immunity rates to range between 10% and 15%.

Antwerp University epidemiologist Pierre Van Damme says the rate suggests the virus isn’t as catchy as was initially thought.

“The research is proof infection occurs through droplets and that people need to be close to become infected. Sticking to distancing measures and sound hand hygiene will have an impact on transmission.”

Good herd immunity involves a general infection rate of around half the population. It means the virus then no longer has free range.

Pierre Van Damme: “We are miles away from the 50%, 60% or 70% herd immunity needed to allow the outbreak to fade away. We will have to live with the virus for a long while. Herd immunity will grow very slowly. Any relaxation of corona measures will have to be very gradual.”

New cases will have to be tracked down very quickly: “The minute there is a new source of infection however small we need to be there. This is the only way to allow any relaxation and it won’t be easy.”

Prof Van Damme suggests that reaching herd immunity without overburdening the health care system will be difficult. “We won’t get there by a natural route. It’s a wait for the vaccine to create immunity artificially. We hope to have a vaccine next year.”

Belgium’s 3% immunity rate mirrors other countries. Austria that imposed restrictions earlier has 1%, the Netherlands has 3%, while Sweden, which took a more relaxed approach to restrictions, is looking at 10%, though that figure still needs to be confirmed.

Prof Van Damme says the countries like the UK and Sweden that counted on herd immunity were wrong: “The virus has spread more widely there, but the impact on health care provisions can be considerably higher too. At the same time you can’t count on herd immunity. In these countries too this will be acquired relatively slowly. It’s a lesson for countries that counted on herd immunity. It wasn’t the right strategy.”

VRT science editor Katty Allaert notes that 3% population immunity is extremely low: “In the meantime it may have risen to 5%, even 10% if we are highly optimistic.”