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Top officials in Japan are increasingly hoping that an “antibody cocktail” treatment will serve as another pillar of the nation’s fight against COVID-19 after months of reliance on vaccines, following the expansion of the scope of the drug’s use beyond hospitalized patients.

The Suga administration eased rules governing its use earlier this month when the health ministry notified municipalities that the cocktail — a combination of two antibodies — can now be used for patients isolating at hotels repurposed as ad hoc medical facilities. Previously, the treatment was limited to hospitalized patients.

The question now is whether the therapy can be further extended to outpatients or those told to isolate at home, a policy shift some medical experts say is necessary amid growing reports of those denied hospitalization dying at home.

A mixture of the monoclonal antibodies casirivimab and imdevimab, the intravenous therapy has been shown in clinical trials overseas to be highly effective in preventing patients from developing severe COVID-19 symptoms. Its efficacy in cutting the risk of hospitalization or death by about 70% has raised hopes that it could go a long way toward stopping hospitals from being swamped with patients that require urgent medical care.

Japan’s approval of the antibody drug, known as Ronapreve, also heralds the advent of a new dimension in its anti-virus strategy, which has for months hinged on a speedy vaccine rollout.

Currently, those eligible for the treatment are patients considered at a high risk of complications from the virus, such as those age 50 or older, smokers and those with conditions including obesity, diabetes and chronic kidney and lung diseases.

The antibody treatment — originally developed by American biotech firm Regeneron Pharmaceuticals Inc. and licensed in Japan by Tokyo-based drugmaker Chugai Pharmaceutical Co. — has drawn praise from Japan’s top leaders: Prime Minister Yoshihide Suga called it “groundbreaking,” while Tokyo Gov. Yuriko Koike billed it as “a new weapon” in the capital’s battle against the pandemic.

The health ministry is more circumspect, however. Although it has allowed the drug to be used for patients at hotels, the ministry is dismissive of any further expansion, citing the possibility of severe side effects that it says make the treatment too risky for patients who cannot be placed under prolonged medical observation.

An intravenous bag used to administer the Ronapreve monoclonal antibody treatment at a clinic in Worcester, Massachusetts, on Aug. 13 | BLOOMBERG
An intravenous bag used to administer the Ronapreve monoclonal antibody treatment at a clinic in Worcester, Massachusetts, on Aug. 13 | BLOOMBERG

Still, the revised health ministry guidelines have already prompted some municipalities to start implementing the treatment at hotels accommodating COVID-19 patients with relatively mild symptoms.

The move has been welcomed by some as making more effective use of the treatment. This is because the antibody cocktail, which needs to be administered within a week of the onset of symptoms to have any efficacy, is not necessarily suited to hospitalized patients, many of whom are already severely ill.

Among the local governments that have started applying the antibody treatment to patients at hotels, or expressed their intention to do so, are Tokyo, Fukuoka, Saitama and Osaka prefectures.

But none of these prefectures has been able to utilize the therapy for hotel patients in a significant way, with Tokyo, Fukuoka and Osaka each going ahead with the treatment at just one hotel out of the many they have opened up to COVID-19 patients.

Behind the slow rollout is the difficulty of procuring medical staff who can administer the treatment, as well as uncertainties about supplies of the drug.

“We were the second prefecture after Tokyo to start giving the cocktail treatment at hotels but if more municipalities start doing the same, I expect the amount we are allocated will decrease,” said Junko Baba, a coronavirus task force official from Fukuoka Prefecture.

“There is no telling how much longer we will continue to be able to secure the amount we want,” she said.

Suga, for his part, insists the government has secured a “sufficient” amount of supply. It has reportedly procured 70,000 doses of the drug, with an estimated 200,000 on the way by the end of this year.

A mixture of the monoclonal antibodies casirivimab and imdevimab, Ronapreve has been shown in clinical trials overseas to be highly effective in preventing patients from developing severe COVID-19 symptoms. | CHUGAI PHARMACEUTICAL CO. / VIA KYODO
A mixture of the monoclonal antibodies casirivimab and imdevimab, Ronapreve has been shown in clinical trials overseas to be highly effective in preventing patients from developing severe COVID-19 symptoms. | CHUGAI PHARMACEUTICAL CO. / VIA KYODO

Still, the amount at the government’s disposal is not infinite, an official from the health ministry’s coronavirus task force emphasized, declining to be named.

“We don’t want to have a situation where some local governments ask for too much under the assumption that supply of the (antibody drug) is somehow unlimited, resulting in others being left without enough,” he said, citing lessons learned from supply shortages that have stymied the vaccine rollout effort in some municipalities.

The cocktail treatment’s effectiveness has ignited calls for its use to be expanded to newly diagnosed patients at home who are awaiting approval for hospitalization, something the health ministry takes a dim view of at the moment. Despite the high hopes expressed by Suga and Koike over Ronapreve’s potential, the ministry maintains a cautious attitude overall.

The antibody treatment “could be followed by pretty serious reactions,” the health ministry official said. “Not to mention, this is a new drug, the effects of which on Japanese people are not entirely known yet. Clinical trial data is limited too.”

A fact sheet issued by the U.S. Food and Drug Administration notes that serious hypersensitivity, including anaphylaxis, and other reactions have been observed during and up to 24 hours after the infusion of the drug.

“Our stance is that the treatment needs to be conducted under the surveillance of doctors,” the official said, explaining the rationale for allowing patients being treated at hotels, which are essentially a simplified version of hospitals, to get the drug.

Critics, however, are not convinced. Some call for the further easing of rules so that outpatients can get the treatment at local clinics or medical professionals can be sent to administer the intravenous drug to those isolating at home.

“There is some logic in what the health ministry says about the need to keep patients under observation long after the infusion, but I think the benefits of giving the antibody treatment to patients at home outweighs the risks of doing so,” said Tetsuya Matsumoto, a professor of public health studies at the International University of Health and Welfare Graduate School who specializes in infectious diseases.

Mastumoto backs the idea of expanding the cocktail’s use to patients told to rest at home and outpatients. He said monitoring patients at home after the infusion is “difficult but not impossible,” saying this can be done by telling them to report any change in their health or asking family members to keep an eye on them.

“My worry is that limiting the cocktail’s use due to excessive concerns about side effects will undermine its availability and deny those who truly need it the chance to use it,” he said.

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