Liang Lianchun, Director of the second department of the Infection Center of Beijing Youan Hospital of Capital Medical University, said recently that second infections may occur in the future, but people need not be too nervous. The prevention measures of a second infection are the same as the ones adopted before. People need to maintain proper self-protection in their daily life and avoid high-risk places and contact with high-risk groups.

Why do patients already recovered from COVID-19 get re-infected? According to Liang, first of all, antibodies produced by novel coronavirus usually do not last long. Based on previous infections of other kinds of coronavirus, the duration of antibody protection is between six months and one year. In the meantime, it cannot be ruled out that the antibodies produced in some people disappear in a noticeably short period of time. As a result, they cannot provide effective protection and re-infections will occur. In addition, it may be due to the mutation of novel coronavirus. For instance, a patient infected with one strain of virus may get infected by a different one, after the previous infection was cured.

A second infection is different from being retested positive, Liang said. When a cured patient of COVID-19 is retested positive, it actually means that he or she was not fully cured, but in a chronic carrier state. There are many reasons for this, such as inadequate testing, failure to acquire samples, or problems with the testing reagents. Some people may carry the virus for a long time, which needs to be further studied.

Will there be more re-infections of cured patients? Liang said this may happen again, but for now it is hard to tell the probability. For example, in China, the probability is relatively low due to our strict epidemic prevention and control measures. But in some countries with less strict measures, the probability could be higher. Or, if the strains of the virus in Asia are different from those in Europe, people from Asia are likely to be re-infected when they travel to European countries.

To some extent, a second infection is usually less severe than first because the antibodies produced by the patient during the first infection can still play a certain role, Liang said. He reminded the public that the prevention measures for a second infection are in fact the same as the ones adopted before. People need to maintain proper self-protection in their daily life and avoid high-risk places and contact with high-risk groups. Getting vaccinated is also an effective means of prevention.