Only three in a hundred people in Belgium have developed immunity to the coronavirus Covid-19, according to a study carried out by the university of Antwerp.
The study gathered more than 3,600 blood samples that had been given by patients for all kinds of other reasons, and tested them for the presence of antibodies.
When a person is infected by a pathogen, the body creates cells which are specific to the infection which are used to fight off the bacteria or virus in question.
This is the principle behind vaccination: an inert or safe dose of a pathogen is introduced into the body to provoke the production of antibodies, which will then be ready to fight if the patient becomes infected normally.
The blood samples used were taken three weeks ago, and antibodies only become visible two weeks after the person became infected. That means that there were some people who were infected by Covid-19 five weeks ago, or just before the lockdown came into force.
The 3% figure, despite dating from very early in the crisis, is lower than researchers expected.
“Three percent is relatively low. So the infection is not that infectious,” said epidemiologist Professor Pierre Van Damme from the university. “It does show that it is a droplet infection, and that people have to be close to each other to pass it on. If we follow distancing measures, and for example keep good hand hygiene, then that will certainly have an impact on the spread of the virus.”
But three percent is far from the percentage required to provide group immunity within the population – where so many people have become immune that the virus has virtually nowhere left to spread to. That figure is at least half, ideally as high as 70%.
That means that measures such as those currently in place can only be dismantled with extreme caution while a vaccine remains a long way off.
“We will only see group immunity growing very slowly,” Prof. Van Damme said. “We will need to ease the restrictions very carefully, step by step, to avoid a flare-up. We are going to have to learn to live with this virus for quite some time yet.”
The screening programme will be repeated every three weeks.