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| A Medical Telegraph from Dr. Kenji Sakai |
The COVID-19 vaccine is expected to not only prevent the development and worsening of symptoms (functional immunity), but to also prevent further infections (sterilized immunity). Of course, preventing symptoms from developing and worsening is important, but preventing outbreaks is just as essential. Even if symptomatic cases decrease, asymptomatic cases will only increase, thereby, making further outbreaks impossible to prevent.
However, at this point in time, we have no definite evidence on how effective the COVID-19 vaccine will be on preventing infections. Additionally, conducting clinical trials to determine if the vaccine provides sterilized immunity will be difficult. The COVID-19 vaccine clinical trials that were conducted were randomized controlled trials (RCT), which is a high-level clinical research method. Comparing the vaccinated group against the control group can prove the effectiveness of the vaccine against developing mild and severe symptoms. However, there is no data on whether the participants have prevented others from being infected.
One of the ways to prove that the vaccine has sterilized immunity is to observe the whole population. If the vaccine prevents infections, then the vaccinated group, combined with the unvaccinated population, should have reduced numbers of symptomatic cases compared to a completely unvaccinated group.
Acquiring evidence to prove that the COVID-19 vaccine prevents infections is still in progress. Israel is taking the lead with the research. They have vaccinated over 20% of the population with the first dose of the vaccine. The data on whether the vaccine is effective on infection prevention will be obtained soon.
However, we should remember that the data from Israel might be different from Japan. Israel implemented a lockdown while also vaccinating the population as measures against COVID-19. Even if Israel reduces their number of new cases in the future, they cannot conclude that it was the effectiveness of the vaccine at work. It is possible that other countermeasures had been more effective in prevention than the vaccine is. Any other research method aside from the randomized controlled trial is believed to produce a lower level of evidence.
During this time, we must consider combining various pieces of information. Different countries are vaccinating their populations at different paces and at different scales. If the vaccine can prevent infections, we can observe the decreasing trend of new infections depending on the scale of vaccination in each country. Even if there is undeniable proof coming from the data of only one country, it would be more convincing to combine different pieces of information to come to a definite conclusion.
In any case, Japan will be able to vaccinate its population a little later. As mentioned before, the vaccine will not work immediately after inoculation. The vaccine is not 100% effective. Even if it may prevent infections, it will not work unless a certain percentage of the population is vaccinated. In the meantime, we must continue implementing our current countermeasures against new infections.
(Dr. Kenji Sakai's series of articles have been compiled into a book.)
The book entitled "A Medical Telegraph: Improving Doctor-Patient Relationships," is a compilation of this series up to this 80th article. (Medicine and Nursing Co., 2138 yen) https://goo.gl/WkBx2i
(Apital: A Medical Telegraph from Dr. Kenji Sakai and etc.)http://www.asahi.com/apital/healthguide/sakai/
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