COVID-19—a very visible pandemic – Author's reply

Let me express thanks to the many colleagues who have provided valuable feedback. I will not address each of these responses individually, but give a collective answer.

One characteristic of the COVID-19 pandemic that has become obvious over the last few months is its irregular spread. It does not move forward in a continuous way from person to person, but rather jumps from one group to another, where the group can be geographical, social, ethnic, and so on. This clustered pattern slows down the spread but, nevertheless, the virus has come to almost every country in the world and taken its high toll of disease and death.

Several studies have been done regarding antibody positivity in Stockholm (with a population of 2·5 million people), with results ranging from approximately 10% to more than 15% of the population being positive and increasing with date of blood sampling.¹ This indicates that some 250 000–400 000 individuals have had the disease. According to the Swedish Public Health Agency's COVID-19 data, as of July 2, 2020, slightly more than 20 000 cases in Stockholm were diagnosed with the use of PCR; in other words, less than 10% of those who are seropositive. A portion of these patients with antibodies probably had quite a severe form of the disease, even if they never sought health care and were tested, but many people have had a mild disease. Much of the spread goes unnoticed by the public health authorities.

Additionally, it might be that cell-mediated immunity plays a bigger role in COVID-19 immunity than understood so far, and that even people who do not have an antibody response can have cleared the infection and be immune.

With regards to public health actions, some countries—primarily island nations—could succeed in eradicating the disease from their country, but at the cost of a strict quarantine for all people entering the country, which might have to be kept up for a long time and have notable societal consequences.

Also, the classic strategy now being adopted by more and more countries to test widely, identify and isolate cases, find and test contacts, and so on, will slow down the spread, but as experience in Germany shows,² outbreaks can become quite large before they are noted and stamped out. It is also doubtful if a strategy of removing lockdowns (whether regional or local) and re-implementing them will be accepted by citizens in the long run.

The hope for the future, of course, lies with vaccines. If an efficacious vaccine is developed, mass produced, and distributed worldwide, then the crisis will be over. The same goes for a preventive or truly curative antiviral therapy, so that there will be no severe cases or deaths. I hope for one or both of these, and soon.