ASOURCE Navi

The peak of the 6th wave of the new coronavirus infection passed in early February this year, but unlike last year's sharp decline after the 5th wave, the pace of decline in infections has been slow and has remained at a high level. Let's consider why.

According to the Ministry of Health, Labor and Welfare, as of April 3, 47,229 people were newly infected with the new coronavirus nationwide. This is only about a 54% decrease from the 103,502 on February 1, the peak of the sixth wave. The fifth wave of the delta strain epidemic, which began last summer, is different from the 98% decrease in the number of infected people in less than two months from the peak on August 20th.

Ministry of Health, Labor and Welfare "Trends in domestic outbreaks of new coronavirus infections (*Number of new positive cases by report date): April 4, 2022"

Experts point out that one of the reasons for the slow decline in the number of new infections in the sixth wave is the delay in the third vaccination. As of early January, less than 1% of people aged 65 and over received the third dose of the vaccine, and even as of February 1, it was less than 10%. In many elderly people, more than half a year has passed since the second vaccination, and the antibody that prevents infection has decreased significantly. seems to have spread. On the other hand, as of late July 2021, when the Delta strain was prevalent, the two-dose vaccination rate for elderly people aged 65 and over exceeded 70%, and infection from young to elderly people was suppressed. rice field.

Another reason is the significant increase in infections among children under the age of 10. The highest number of infected children under the age of 10 in the fifth wave was 10,380 in the week ending August 31, 2021, while the highest number so far in the sixth wave was in 2022. It was 76,856 for the week ending March 8th. It has been pointed out that the 6th wave Omicron strain is more infectious than the delta strain, and that it spreads easily in environments where people live in groups such as kindergartens and schools, and that the vaccination rate of children is low. Corona vaccines for 5 to 11 year olds have been in full swing since March. , at 5.3%.

Ministry of Health, Labor and Welfare "The 77th New Coronavirus Infectious Disease Control Advisory Board (March 23, 2022) Material 2-3 Changes in the number of new positives (HER-SYS data)"

In addition, the influence of the Omicron strain derivative "BA.2", which is said to be more infectious, is also considered to be a factor. The original phylogenetic strain ``BA.1'' has been rapidly replaced, and it is believed that the majority of new infections may be infected with BA.2, and is expected to reach nearly 100% in May. I'm here. Compared to BA.1, BA.2 takes 15% less time to infect others after infection, and has a 26% higher effective reproduction number, which is an index that shows how many people an infected person will infect next on average. and Other countries with increasing rates of BA.2 are experiencing resurgence of infections.

As the number of new coronavirus infections began to decline, the priority measures to prevent the spread of the virus, which had been applied to 18 prefectures, were completely lifted on March 22 for the first time in about two and a half months. Some areas have high standards. It has also been pointed out that there is concern that the BA.2 will be replaced by BA.2, and that the tourist season will be approaching, and that the infection will spread again from spring to summer, leading to a seventh wave.

Under these circumstances, the government has begun considering the 4th vaccination of the new coronavirus aiming to start in May. This is based on the fact that the infection prevention effect tends to decrease after a certain period of time has passed since the third vaccination. In any case, it is necessary to continue basic infection control measures such as avoiding the 3Cs, thoroughly ventilating, wearing a mask, and washing hands.