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As Japan’s delta-induced fifth wave of COVID-19 wanes and the inoculation campaign continues, scientists are continuing to gather more data on vaccines and their effectiveness against the highly contagious variant.

While vaccines do not offer 100% protection against delta, or any other form of the virus, public health experts have repeatedly found that COVID-19 shots are effective at preventing hospitalizations and visits to emergency departments.

Here are some key questions and answers regarding COVID-19 shots and the delta variant:

Why is inoculation essential in combating delta?

Delta is considered more than twice as contagious as strains that were prevalent at the beginning of the pandemic. Some research suggests that delta might cause more severe illnesses in unvaccinated people than other variants. The American Centers for Disease Control and Prevention (CDC) said the risk of infection is eight times higher in the unvaccinated than the vaccinated, and the risk of hospitalization or death is 25 times higher.

Over the summer, the delta mutation of SARS-CoV-2 took over in Japan and in many other parts of the world.

As of Sept. 15, Japan had 20,901 confirmed delta infections nationwide following a spike by 5,238 cases within the week of Aug. 30 to Sept. 6. However, the officially reported figures are said to only reflect a portion of infection numbers given that not all viral samples are screened for all variants.

The delta variant is also responsible for more than 98% of new coronavirus infections in the U.S. A high delta infection rate naturally brings about concerns over the effectiveness of existing vaccines and treatments, especially when taking into account the higher viral load seen with delta infections.

A recent pre-print study by researchers at the Chinese Academy of Medical Sciences also found that viral loads in delta infections are around 1,000 times higher than those caused by other SARS-CoV-2 strains. Therefore, as the World Health Organization warns, a higher level of antibodies is needed to overcome delta compared to other variants like alpha. WHO experts have stressed that being fully vaccinated is essential to developing full immunity against delta.

A health care worker holds a syringe filled with the Moderna Inc. vaccine at a mass vaccination site in Saitama on Aug. 23. | BLOOMBERG
A health care worker holds a syringe filled with the Moderna Inc. vaccine at a mass vaccination site in Saitama on Aug. 23. | BLOOMBERG

Results of research published July 21 in the New England Journal of Medicine show that after one dose of either vaccine, the estimated effectiveness was lower against delta than against alpha, which had been prevalent before. “After two doses, however, vaccine effectiveness was high,” the research said.

How do vaccines fare against the delta variant?

While public health experts have been assuring people that immunity developed through vaccines protects individuals from catching the delta mutation of the coronavirus, the effectiveness of the jabs does appear to wane over time.

Of a number of vaccines developed worldwide, Japan has authorized only the Pfizer-BioNTech, Moderna and AstraZeneca-Oxford shots so far.

A recent major study conducted by researchers from Britain showed that the effectiveness of the Pfizer-BioNTech vaccine in preventing people from developing a high viral load from delta stood at 92% 14 days after an individual received their second dose.

However, the effectiveness dropped to 90% after 30 days and then to 85% and 78% after 60 and 90 days, respectively. In the study, which was conducted by the University of Oxford and the local Office for National Statistics, the researchers used PCR tests to detect the virus. The findings were published pre-print in the science journal Nature on Aug. 19.

The same study showed that test results conducted using samples from people inoculated with the vaccine developed by AstraZeneca PLC and Oxford University was 69% effective against a high viral load 14 days after the second dose, with effectiveness falling to 61% after 90 days.

The researchers analyzed the results of some 2.58 million tests for SARS-CoV-2 from 384,543 adults between Dec. 1, 2020 and May 16, when the alpha variant first identified in the U.K. was dominant in many parts of the world. They compared the results with those based on 811,624 tests from 358,983 people between May 17 and Aug.1, a period where the delta variant was more dominant.

Of the three shots available in Japan, Moderna may fare the best against the delta variant. Some data show that its efficacy could reach even 95% soon after inoculation. On top of that, findings in a U.S. pre-print study on some 50,000 patients in Massachusetts showed that Moderna’s efficacy dropped from 86% in early 2021 to 76% in July. The study was conducted by the Mayo Clinic and clinical data analytics platform nference Inc. based on data from January to July. The results showed that the effectiveness of the Pfizer vaccine had fallen to 42% from 76% in the same period. The result was a significant drop in protection from the vaccine’s 95% efficacy in clinical trials.

How do vaccines protect inoculated people from delta?

Studies on delta suggest that people who have been vaccinated are much more likely to avoid hospitalization.

According to a U.S. study, released by Morbidity and Mortality Weekly Report, an epidemiological digest published in the U.S. by the CDC, the Moderna shot was 95% effective at preventing hospitalizations among adults age 18 and older. Meanwhile, the Pfizer vaccine was 80% effective and the Johnson & Johnson vaccine, which is not authorized for use in Japan, stood at only 60%.

A group of researchers from the CDC has analyzed more than 32,000 medical encounters from nine states in June, July and August. The results showed that unvaccinated individuals with COVID-19 are 5 to 7 times more likely to need emergency department care or hospitalization.

“The main goal of these vaccines is really to prevent severe disease, because what we want for people, even if they get the infection, is for them to recover from it and not become seriously ill,” said WHO’s Chief Scientist Soumya Swaminathan in a statement released July 1. The Indian pediatrician, who is a globally recognized researcher on tuberculosis, said that the vaccine’s efficacy in preventing hospitalization even exceeds 90%. She explained that infection with the delta variant following inoculation would likely result in “very mild symptoms or no symptoms at all and that the chances of getting seriously ill are really, really low.”

Residents wait in line to receive the COVID-19 vaccine at a mass vaccination site in Saitama on Aug. 23. | BLOOMBERG
Residents wait in line to receive the COVID-19 vaccine at a mass vaccination site in Saitama on Aug. 23. | BLOOMBERG

The vaccines also proved effective at preventing urgent care visits. Moderna was 92% effective, Pfizer was 77% effective, while Johnson & Johnson was 65% effective, the study said.

Given that the delta variant has become the dominant mutation in Japan, the government appears keen to follow countries like the U.S. in arranging vaccine boosters potentially by the end of the year to help improve immunity.

Are there vaccines developed specifically for the delta mutation?

Yes. Germany-based BioNtech began clinical trials in August on a new type of vaccine that targets the delta variant. However, according to the company, even though the vaccines can be produced in six weeks to 100 days, the trials are currently being conducted for research purposes, given that the mRNA vaccines already in use have proven effective against various coronavirus mutations, including delta.

The vaccine the firm co-developed with Pfizer allows the body to produce viral proteins in cells by injecting artificially produced mRNA, as opposed to vaccines requiring the use of a real virus for development, a technique that was more common in the past.

But the company is still betting on improved immunity through a third dose of the existing vaccine.

Are there treatment options for delta infections?

On July 19, the health ministry granted the world’s first regulatory approval for the use of Ronapreve, manufactured by Chugai, for treating mild to moderate symptoms of COVID-19. The move came amid a surge in delta infections and was the fourth treatment option introduced in Japan. But Ronapreve, in particular, raised hopes that it would prove effective against delta.

In clinical trials, the medicine effectively stopped symptoms from worsening after a single dose.

“In order to bring the pandemic under control as soon as possible, it is extremely important to prevent new infections with vaccines and to expand the treatment options for people with COVID-19,” said Osamu Okuda, Chugai’s president and CEO.

He explained that Ronapreve reduced the risk of hospitalization or death. He added that the therapy has proven to be effective against multiple variants, including delta, in non-clinical studies.

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