This is our series on key information related to the coronavirus. Click here to read other episodes: #Coronavirus the facts. Find the latest information and expert answers on all things COVID-19.
Fourth dose under discussion
Japan’s health ministry is considering allowing a second booster, or fourth dose, of a coronavirus vaccine because the effectiveness of a third dose would wane over time. Although no decision has yet been made, the ministry says local authorities are expected to complete preparatory work for a deployment, arranging vaccination coupons and venues, by the end of May.
Slow setting for booster shots
Although more than 80% of elderly people in Japan have received a booster shot, the rate for the general population was only 44% as of April 7. Some experts say the delay is one of the reasons for the failure to bring the infection rate down. under control.
Research in Israel
Research has shown that a third shot is more effective against the Delta variant than the currently dominant Omicron variant. Efficiency also decreases over time. As a result, some nations have already begun administering fourth injections.
On March 16, the New England Journal of Medicine published the results of a study in Israel which found that the first booster was essential for maximizing immunity and that a second booster was effective primarily in restoring antibody levels. which had decreased since a third dose.
The researchers examined 154 medical workers who had received a Pfizer vaccine for their fourth dose and 120 medical workers who had received the Moderna vaccine. They found that the two vaccines were only one-tenth as effective against Omicron as against the original virus. They say a fourth dose for young, healthy people may have only marginal benefit.
Pfizer claims that when people aged 60 or over receive a fourth injection more than four months after a third injection, it halves the number of infections and reduces the number of people who develop severe symptoms by 75%.
Around the world
On March 29, the United States Food and Drug Administration authorized a fourth dose of the Pfizer-BioNTech and Moderna vaccines for people aged 50 or older who received their third injection at least four months ago, and for immunocompromised people under 50.
The UK, France, Germany, South Korea and Israel are already offering second booster shots, in most cases limited to the elderly, nursing home residents, medical staff and immunocompromised people. .
No need to rush
Immunologist Miyasaka Masayuki, a visiting professor at Osaka University’s Center for Frontier Research in Immunology, says that while the ability to prevent severe disease may decline, a resurgence can be expected. efficacy after a fourth injection, based on data from Israel among other sources.
He says that the level of neutralizing antibodies rises to a certain level after a fourth shot and that is sufficient from an immunological point of view.
“The immune system could be weakened, especially in the elderly and people with underlying health conditions such as diabetes and heart problems, so they are very likely to be the target of the fourth dose,” Miyasaka said. “We don’t need to rush to deliver a fourth dose, but it is important to be prepared for it as variant strains with higher pathogenicity or infectivity may emerge.”
As for the vaccination interval, he does not recommend receiving a fourth too soon after a third dose, and that leaving a sufficiently long interval can produce high-quality antibodies.
He says that a third dose activates B cells, a kind of immune cell, which create antibodies, so before a fourth dose, waiting a sufficient period of time to develop B cells is very likely to produce antibodies that can respond to various variant strains.
Take the first reminder, prepare for the next
Professor Hamada Atsuo of Tokyo Medical University Hospital, an infectious disease expert, said it was good to provide a fourth vaccine to the elderly who are at higher risk of serious illness and to medical workers about six months later. their third. But, he also points out that the current priority is to increase third-hit coverage to over 50% in April or May to seek an exit strategy to get society and the economy back on track. Our immediate challenge is to continue to take basic anti-infection measures and, at the same time, to bring daily life back to normal.
This information is accurate as of April 8, 2022.