In Wuhan, China, where the pandemic began in December last year, people are now looking for antibodies to the coronavirus in the population.

The studies have so far resulted in both good and bad news. The good thing is that significantly more people appear to carry antibodies than the number of confirmed cases, which indicates that many who have been infected have had only mild or no symptoms at all. The bad thing is that only 2-3 percent of the test subjects carried antibodies.

"That means a herd immunity is far away, so a vaccine might be our last hope," Wang Xinghuan, director of Zhongan Hospital, one of the largest in Wuhan, told the Wall Street Journal.

Uncertain answers

The proportion of the population that must be immune to a particular virus is related to its infectiousness. The more infectious a virus is, the greater the proportion must be immune in order for a spread of infection not to occur. Nobody knows what percentage of the population must be immune to the corona virus, but experts say this percentage should be at least 50, maybe 60, percent.

Another question is to what extent an infection with the corona virus results in becoming immune to the virus. Does this also apply to those who have only had mild or almost no symptoms at all? Neither do the scientists. Antibody tests are already being sold to private individuals in Sweden, but several researchers and even the Swedish Medicines Agency have warned of these tests.

"It's not safe to be immune just because you have antibodies," Lin Xihong, a professor of biostatistics at Harvard TH Chan School of Public Health, told the magazine.

The tests themselves can also be unsafe.

A quarter

In Wuhan, there are several cases where people who have become ill from the virus have recovered and tested negative for the presence of antibodies, only to have tested positive later. Whether this is due to the tests or whether the people have been infected a second time, the researchers do not know. But it puts our finger on how little we know so far about the immunity that possibly follows from an infection, which in turn can affect the herd immunity that some countries, including Sweden, put their trust in.

Antibody studies have also been conducted in Sweden, but so far only on a small number of people. However, based on these and other modeling, the Public Health Agency believes that 26 percent of Stockholmers will have had the infection in early May. If these people have also become immune, then it remains to be seen.