Omicron strain BA.5 has brought the seventh wave to Japan, and is expected to completely replace the BA.2 strain in early August.
In the past two weeks, the number of patients with new crown has risen sharply, and on July 14, it exceeded 50,000 cases per day for the first time in four months (Japan Ministry of Health, Labor and Welfare). In Tokyo, on July 12, the number of new cases also exceeded 10,000 for the first time in four months, with the alarm level being raised to "the worst".
■ "People who have suffered this disease before" and "people who have suffered this disease" may be infected.
The tense atmosphere has returned to the medical field.
It is shocking that positive cases have appeared one after another, even among those who have received appropriate additional vaccines.
There are also reinfection. Not only Delta strains and early strains, but those who recovered from early Omicron strains, BA.1 and derivative strains, BA.2 were also infected with BA.5.
It seems that it is true that BA.5 is prone to "immune escape".
Immune escape means that the virus effectively resists the attack of "neutralizing antibodies" obtained through previous infection or vaccination. In other words, BA.5 seems to have developed a more complex approach to glide over the "face recognition system" of immunity gained through previous infections and vaccines.
A study from China reported in May. They used blood from people who had received three doses of Sinovac vaccine (inactivated vaccine) and those who experienced BA.1 infection after getting vaccinated, and found that BA.4 and BA.5 showed stronger immune escape than BA.2.
A recent paper published by Harvard in the New England Journal of Medicine also showed that BA.4 and BA.5 clearly avoided previous infections and immunity of the Pfizer vaccine.
Blood samples from 27 people who have completed three doses of the Pfizer vaccine or have previously been infected with BA.1 or BA.2 showed that the neutralizing antibodies to BA.4 and BA.5 were only about one-twentieth of the new coronavirus (a conventional strain found in the United States) in the early stages of the pandemic. Compared with BA.1 and BA.2, is only about one-third.
It must be said that the chance of avoiding BA.5 infection is greatly reduced compared to traditional strains, even if the person has been infected before, even if he or she has been given an additional dose of the current vaccine.
is four times more contagious than delta strains?
Nevertheless, the government now announces that it intends to expand the number of people eligible for additional vaccinations, including the third dose for children aged 5-11, and the fourth dose for healthcare workers and staff at elderly care facilities, previously limited to the elderly and those at high risk for severe illness.
The government, which has always been optimistic, seems to be threatening the rapid increase in the number of infected people.
First of all, how shocking is BA.5? It is said that the early Omicron strain BA.1 is also very contagious, but is there really that big difference between BA.1 and BA.5?
In a comprehensive study of many papers, the basic reproduction number of BA.1 (how much infection transmitted from a patient in an immunity population) is 8.2, 3.5 times that of the Delta strain, and the effective reproduction number (how much infection transmitted from a person in an already infected population) is 3.6, 2.5 times that of the Delta strain.
The 'BA.2' strain from BA.1 has higher infectivity. The Japanese national research report also pointed out that the effective reproduction number of BA.2 is 1.4 times that of BA.1.
is said to be even higher than BA.5. According to data from the National Institute of Infectious Diseases, according to data from Tokyo, the effective reproduction number of BA.5 is about 1.27 times that of BA.2.
A simple calculation (rather inaccurate) showed that compared with the early Omicron strain, the infection rate of BA.5 was 1.4×1.27≈1.78 times, while compared with the Delta strain, the infection rate was 1.78×2.5=4.45 times.
In addition, studies conducted by the Institute of Medical Sciences at the University of Tokyo show that BA5 may cause serious diseases more easily than BA.1.
Compared with hamsters infected with BA.2, the virus level around the lungs of hamsters infected with BA.4 and BA.5 increased by 5.7 times after three days, and still increased by 4.2 times after five days. The virus levels around the lungs are also higher, suggesting that the virus spreads to the lungs more efficiently than BA.2.
Extra vaccination with conventional vaccine "Is it meaningful?
What can we do now in the face of BA.5? It is therefore "highly contagious" and "more likely to cause serious illness"?
You may think, "Even if I get the current vaccine, BA.5 will still happen, so what's the point? "You might think," but that's not true.
Vaccines not only induce immunity through antibodies (humoral immunity).
The immune system also contains lymphocytes, namely "killer T cells", which can eliminate viruses (cellular immunity) in infected cells. It has been pointed out that even if the antibody decreases over time or the virus strain repeatedly mutates, this function may be maintained above a certain level.
Regarding BA.1, the National Institute of Infectious Diseases noted that "the decrease in cellular immunity to the omega strain is limited compared to antibodies", "in those who recover from infection and those who were vaccinated, at least 70% of T cells that responded to the Wuhan strain also responded to the omega strain."
About BA.5, it can be seen that cellular immunity can play a role to a certain extent.
Cell immunity may be particularly helpful in preventing serious diseases. Because BA.5 is susceptible and proliferates in the lungs, it is necessary to prevent serious diseases by promoting vaccine-induced cellular immunity, even more necessary than previous Omicron strains (BA.1 and BA.2).
'Aren't you developing a vaccine for Omicron? People might say, 'I want to wait for this'.
Since the first appearance of the Omicron strain (BA.1), some people have pointed out that it has mutations that promote immune escape. This prompted us to develop the Omicron vaccine, which adds information from the Omicron strain to the immune "face recognition database".
As of December last year, Pfizer said it could supply Omicron vaccine in March this year ( Wall Street Journal ). Moderna also believes that mass production will be achieved within a few months (Financial Times).
It seems that things have not developed according to this view, but both companies are now close to completion.
Omicron vaccine "Is it effective for BA.5?
On June 8, Moderna announced that the 50 microgram Omicron vaccine in clinical trials was injected into more than 800 participants as an additional dose (the fourth dose), and the neutralizing antibodies against the Omicron strain were increased by 8 times (BA.1).
Pfizer also announced on June 25 that 1,234 study participants had been injected with 30 or 60 microgram Omicron vaccine, resulting in a 13.5 and 19.6 times increase in neutralizing antibodies against BA.1, respectively.
The company is also developing a bivalent vaccine, a mixture of traditional vaccines and Omicron compatible vaccines, which increased the neutralizing antibodies against BA.1 and Omicron 9.1 and 10.9 times, respectively.
However, the virus has continued to mutate over the past few months, with the mainstream replacing BA.1 with BA.2 and then BA.5, which showed stronger immune evasion ability.
On June 30, the U.S. Food and Drug Administration (FDA) issued a statement asking vaccine manufacturers to produce new BA.4 and BA.5 supplemental vaccines.
As of June, Pfizer admitted that its upcoming Omicron vaccine was not as effective as BA.1, although its neutralization effect on BA.4 and BA.5 has been confirmed.
On the other hand, on July 11, Moderna reported that the bivalent vaccine (a combination of traditional vaccines and Omicron-compatible vaccines) that are currently applying for approval in various countries have obtained targeting BA.4 and BA.5. "A significant higher neutralizing antibody response".
The neutralizing antibody titer of the additional traditional vaccine has increased by 3.5 times, the new vaccine has increased by 6.5 times, and the geometric mean difference is 1.69 times.
As of the current announcement, Moderna seems to be one step ahead of Pfizer in terms of BA.5-compatible vaccines.
Even so, commercialization is expected to be achieved this fall; the peak of the BA.5 epidemic has long passed (coincidentally, the new infection wave in 2020 and 2021 reached its peak in August. We will see what will happen this August...).
is more important than waiting for a "vaccine that meets BA.5 standards."
Now, the BA.5 wave is about to swallow us, and it is wise to use vaccines that can be injected immediately to ensure the reduction of the number of serious cases.
As mentioned earlier, the Japanese government, which has remained silent so far, has finally announced a policy to expand the number of people eligible for vaccination.
According to data from the Japanese government (July 11), the vaccination rate for the third dose of the vaccine for people over 60 is more than 80%, but the drop to more than 75% for people aged 50, about 60% for people aged 40, about 50% for people aged 30, 40% for people aged 20, and only about 30% for people aged 12-19.
Because it is not mandatory, it is difficult to impress those who are capable but are unwilling to be vaccinated. However, the above figures can also be interpreted as "there are a certain number of people of every age who are willing to receive vaccination."
Although there may be a large number of young people who want to get vaccinated for the fourth time, they don’t seem to be worried about a shortage of vaccines all at once.
It is important to establish a system so that those who want to get vaccinated can get vaccinated. Make sure those who can protect themselves with vaccines can receive the vaccine and protect those who cannot.
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