It has now been one year since the COVID-19 pandemic began to spread around the world. More than 100 million cases and 2.5 million deaths have already been reported. Compared to Europe and the United States, the number of patients and deaths in Japan is lower, but the current situation remains unpredictable.

However, unlike one year ago when the future seemed uncertain, we are beginning to see a glimmer of hope ahead.

A succession of effective vaccines for the new variant have been developed and vaccination has begun. Japan appears to have started its vaccination program later than Europe and the U.S. not only perhaps because domestic production is still not possible, making it necessary to rely on imports, but also due to the low number of deaths from infection. It seems that just recently Australia, New Zealand, and South Korea, which have fewer cases than Japan, have also finally started their vaccinations.

Information from the U.K., the first country to administer a vaccine, and the U.S., indicates that vaccination is highly effective. According to an article in the New York Times on February 1, 2021,^*1 a follow-up survey of the 75,000 vaccine recipients in the early stage of the trial found that not a single person died from the COVID-19 virus during a 28-day period after vaccination. Since a calculation of the COVID-19 virus rate of infection in the U.S. over a 28-day period with no vaccine administered comes to a total of 150 deaths out of 75,000 cases, the result of the survey substantiates the tremendous effectiveness of the vaccination.

However, even in the United States, public opinion polls indicate that one in three people do not want to be vaccinated due to concerns about side effects.

In Japan as well, although some people eagerly await the vaccine, there are those who reject it out of fear of side effects, in particular, anaphylaxis. In this article, I would like to discuss the distinguishing features of the newly developed COVID-19 vaccine and the actual condition of its side effects.

Features of COVID-19 Vaccine

Before explaining the new vaccine, let's briefly review how vaccines work. Vaccines are a method of preventing infection by immunity, the ability to break down and eliminate foreign proteins in the body. Bacteria and viruses have proteins that are not found in the human body. When foreign proteins enter the body, a particular type of lymphocyte cell (microphage) ingests the virus or bacteria or a part of it (phagocytosis), and the features are analyzed in the lymphocyte cells and conveyed to particular lymphocyte cells (killer lymphocytes) that can efficiently analyze the bacteria and virus. Furthermore, it also stimulates proliferation of lymphocyte cells (B. lymphocyte cells) that produce proteins (antibodies) that attach to virus and bacteria, destroying them and producing large quantities of antibodies.

Vaccines in the past were classified into two broad categories. First, there is the attenuated vaccine. In the case of measles, for example, this refers to a vaccine that is a liquid containing an attenuated measles virus in which the measles virus is dispersed and weakened. Protein in the attenuated measles virus is about the same as that found in the strongly poisonous typical measles virus (wild strain), so for that reason, if we are vaccinated, just as if we had been infected by the usual measles virus in our bodies, a large number of killer lymphocytes and antibodies are created instantly, and thereafter even if we are exposed to the virus, it is possible to prevent infection.

Another type of vaccine does not contain an attenuated virus (bacteria), but includes rather bacteria or a virus that is not infectious after death (component vaccine). When used, although it does not cause infection like live vaccine, it immediately produces lymphocytes and antibodies that react to bacteria and viral proteins, and prevents infection by bacteria or live virus. Influenza vaccine and the DPT vaccine are types of such "component vaccines."

Among vaccines that are effective against COVID-19, added to vaccines that are made by the same method as the usual component vaccines (the Chinese vaccine), there is now a vaccine that is effective in a totally new way. One is the mRNA vaccine developed by Pfizer and Moderna.

Virus, bacteria and the cells that make up our bodies contain strands of macromolecules with genetic information such as DNA or RNA. DNA and RNA operate as a kind of template when cells produce protein. At that time, the original DNA or RNA is transcribed into instructions on a messenger template called mRNA, which then serves as the basis for making protein. The mRNA vaccine for the COVID-19 virus contains a message that triggers cells to make protein in the form of a spike that hooks onto the surface of human cells infected by the virus. In this state, because mRNA easily breaks down due to oxygen in the body, it is artificially overlaid with special liposome. The liposome layer attaches to the surface of muscle cells tissue, and at that time, the mRNA inside penetrates the muscle cells. Because the mRNA is not a virus, but a chemical substance, it does not multiply there, but the muscle cells recognize the mRNA as something that they have made, and synthesize the COVID-19 spike protein in the muscle cells. In humans, because the spike protein is a heterogeneous protein, in the same way that lymphocytes respond to the spike in COVID-19, killer lymphocytes and antibodies will be produced. From now on, this will be the same for live attenuated vaccines and component vaccines.

The mRNA vaccine or (Messenger RNA vaccine) has many advantages. First, as is the case when making live or component vaccines, there is no need to cultivate the virus (bacteria), a task that requires considerable time and effort. The mRNA vaccine can be made artificially by current methods of genetic engineering so that unlike component vaccines, impurities do not enter, and furthermore, if the virus mutates, it is possible to immediately make a new vaccination based on the genetic sequence data of the mutation. This technology has been known since 1989, and now due to the current COVID-19 pandemic, its practical application has suddenly accelerated. Using DNA, not mRNA, Johnson & Johnson has developed a vaccine that synthesizes the spike protein of COVID-19.

Regarding anaphylaxis

An anaphylactic reaction occurs when the immune system overreacts to protein or other foreign substances in the body, causing the expansion of blood vessels throughout the body and possibly a state of shock. This rarely occurred with vaccines for measles and other viruses, but with the totally new type of mRNA vaccine, the degree to which anaphylaxis is possible is not known, which has caused considerable anxiety and concern.

Cases of anaphylaxis resulting from the mRNA COVID-19 vaccine have already been reported in the U.S. where inoculation began earlier than in other countries^*2. Anaphylaxis was reported in 47 people of the 9,943,247 who received the Pfizer vaccine（0.00047%= 4.7 per 100,000） and 19 of the 7,581,429 who received the Moderna vaccine (0.00025% = 2.5 per 100,000). Of the 47 cases of anaphylaxis after receiving the Pfizer vaccine, 16 had a medical history of anaphylaxis, and of the 19 cases of anaphylaxis after the Moderna vaccine, 5 had a medical history of anaphylaxis. If no measures are taken to deal with anaphylaxis, the consequences can be fatal, but treatment (adrenaline injection, etc.) can be readily provided. Regarding the above statistics, because 90% of the cases occur within 30 minutes of inoculation, the current practice of having those who receive the inoculation remain on site for thirty minutes afterwards is an adequate measure.

Even in Japan where the death rate due to COVID-19 is much lower than in North America, (1 in 16,000 in Japan compared with 1 in 640 in the U.S.), it is good to keep in mind that the death rate from COVID-19 infection is much higher than the danger posed by anaphylaxis.

• *1 New York Times, Feb. 1, 2021.
  https://www.nytimes.com/2021/02/01/briefing/vaccination-myanmar-coup-rochester-police.html
• *2 Shimabukuro TT, Cole M, Su JR. Reports of Anaphylaxis After Receipt of mRNA COVID-19 Vaccines in the US--December 14, 2020-January 18, 2021. JAMA. Published online February 12, 2021. doi:10.1001/jama.2021.1967