When will the infection spread of COVID-19 end?

Everyone wants to know the answer to this question. Of course, I do not know what the correct answer is, but at least I can tell you what conditions are necessary for the epidemic to end. In this post, I would like to explain what they are.

First of all, if this SARS-CoV-2 is a seasonal virus like the influenza virus or rotavirus, it will naturally wane according to the change of seasons, or the epidemic will be brought under control. Since the old type of coronavirus, which causes the common cold, is a seasonal virus that becomes active in winter, if SARS-CoV-2 retains such characteristics, the epidemic should naturally abate as the weather warms up. However, it has not been verified if SARS-CoV-2 has inherited those characteristics of the old type coronavirus. Moreover, the epidemic is very severe in countries with high temperatures and high humidity, so we may not expect too much. Still, we cannot rule out the possibility yet.

It is not impossible to stop the spread of virus before it affects the whole of Japan if we carefully terminate the spread from each cluster, even though it does not cease of its own accord. There are now only a small number of newly infected cases in China. It may be that they have succeeded in containing the epidemic before it spreads to the whole populace. However, in this case, many of the population have not been infected yet, so they lack antibodies. If SARS-CoV-2 is brought in again from overseas, etc., in the future, there is the risk of a recurring outbreak of the epidemic.

The above two potentialities may not be expected to happen in Japan where we have an increasing number of COVID-19 patients whose route of infection has not been verified. In that case, there will be three possible scenarios, which I will now explain.

Generally speaking, viral infection ceases its prevalence when a certain number of the population become infected and cured or obtain antibodies by vaccination. For example, we do not see a pandemic of measles in developed countries. That is because most of the population receive immunization at an early age and have antibodies. Still, in developing countries where there is insufficient provision of measles vaccine, epidemics of measles do occur among unvaccinated children, with high numbers of fatalities. According to research by the World Health Organization, it is estimated that 30 to 40 million people (many are children) become ill due to measles with approximately 750,000 fatalities.

It is estimated that SARS-CoV-2 will be contained when ultimately 60% to 70% of the population develop antibodies. In fact, the German Chancellor Angela Merkel pointed this out in her message to the nation.

Then what are the three scenarios whereby 70% of the population can develop antibodies for SARS-CoV-2? In the first scenario, 70% actually become sick with COVID-19, from asymptomatic infection to the critical stages. If we assume that this condition occurs without treatment drugs to cure it (though we do have some candidate drugs), theoretically 1% to 3% of critical condition patients will die. Obviously, this is the worst-case scenario that we want to avoid at all costs.

The second scenario is the development of an effective vaccine to bring the fatality rate down close to zero, just like the case with measles. This is the best-case scenario.

The third scenario is a combination of effective treatment drugs and artificial respirator treatment for patients in critical condition to markedly decrease fatalities, while patients in mild to moderate condition will recover from infection by developing antibodies naturally even though no vaccine has been developed.

I hope we can avoid the medical system to collapse from an explosive surge in infection rates and this pandemic will end without going into the worst-case scenario.