Covid-19 column: Here’s how well Covid-19 vaccines work against the Delta variant



The United States is now dealing with the delta variant of the coronavirus, a highly contagious variant that was first identified in India in December.

As with previous variants, the delta variant has spread to many countries across the world, including, most notably, the United Kingdom, where it’s now responsible for around 99% of new cases.

The United States first announced that it had diagnosed a case with the delta variant in March this year. It’s now the dominating variant nationwide, making up more than half of all new infections in the country.

Confirmed infections with the delta variant have also been doubling since June. The average is more than 24,000 a day, according to data from the Centre for Disease Control and Prevention (CDC).

This rise has been attributed, in part, to the delta variant being an estimated 60% more transmissible than the alpha variant, according to recent research.

Additionally, areas with low vaccination rates are more likely to see a surge in infections.

Low vaccine uptake driving up infections

“The unvaccinated population is at high risk for infection. If this variant continues to move quickly, especially in areas of low vaccination rates, the U.S. could see a surge in SARS-CoV-2 infection,” said Dr. Miriam Smith, chief of infectious disease at Long Island Jewish Forest Hills Teaching Hospital in Queens, New York City.

CDC Director Dr. Rochelle WalenskyTrusted Source issued a warning on this potential surge earlier this month.

In a press briefing, she said preliminary data suggested that 99.5 percent of the people who died from Covid-19 since January were unvaccinated.

“We know that the delta variant… is currently surging in pockets of the country with low vaccination rates,” she said.

In Missouri, which has a vaccination rate of 40.26%, confirmed coronavirus infections have almost doubled in the past 2 weeks.

In contrast, Vermont reported only 32 cases on July 12 and currently has one of the highest vaccination rates in the country at 67.70%.

This echoes findings from a U.K. studyTrusted Source that found the delta variant twice as likely to lead to hospitalisation, and both the AstraZeneca-Oxford and Pfizer-BioNTech Covid-19 vaccines being effective in reducing this risk.

“We also know that our authorized vaccines prevent severe disease, hospitalization, and death from the delta variant,” Walensky said.

Dr. Theodore Strange, the interim chair of medicine at Staten Island University Hospital in New York, said the data supports this.

“The safety and efficacy of the current vaccines are very clear. These three vaccines do work to prevent disease and the spread of disease, and they are as safe as any other vaccines that have been in use. Although some side effects have been reported, these issues are rare and treatable,” he told Healthline.

Vaccine progress in the U.S.

The United States has so far administered more than 336 million doses of Covid-19 vaccine. Around 160 million people have received two doses. That means more than half of the U.S. population over the age of 12 — or 56.6% to be exact — has been fully vaccinated.

There are currently three Covid-19 vaccines that have been authorized by the Food and Drug Administration (FDA) and are currently in use across the United States.

The Pfizer-BioNTech vaccine was the first to receiveTrusted Source emergency use authorization (EUA) from the FDA. It’s sold under the brand name Comirnaty and is also referred to as BNT162b2. Currently, more than 186 million doses of the vaccine have been administered in the United States.

A week after the Pfizer-BioNTech vaccine EUA, the Moderna vaccine also got the green light from the FDATrusted Source. Sold under the brand name Spikevax and also known as mRNA-1273, more than 136 million doses of the Moderna vaccine have been administered in the United States so far.

The third vaccine approved by the FDA was the Johnson & Johnson COVID-19 vaccine, or Janssen COVID-19 vaccine. It was issued an EUA in February 2021Trusted Source. Around 13 million doses have been administered so far.

Vaccines vs. delta variant

All three vaccines are proven to be effective in varying degrees against the original variant of the coronavirus, SARS-CoV-2, that causes Covid-19.

However, since the delta variant emerged, scientists have been trying to establish whether these vaccines are as effective against it.

We broke down what the current data says. But new research could mean this data will change over time.

The Pfizer-BioNTech Covid-19 vaccine

Due to limited research so far, trying to determine the effectiveness of each vaccine against the delta variant remains a challenge. However, there have been promising results from multiple studies.

Study 1 and real-life data

According to an analysis carried out by Public Health England, two doses of the Pfizer-BioNTech vaccine appeared to be about 88% effective against symptomatic disease and 96% effective against hospitalization with the delta variant.

The same study suggested that the vaccine was approximately 80% effective against preventing infection from the delta variant. Scientists came to this conclusion after analysing 14,019 people with an infection, 166 of whom were hospitalized, in England.

Vaccines had a protective effect against infections with delta and hospital cases were milder, the study found.

Public Health England also shared real-world data in May that solidified the importance of having a second dose of Covid-19 vaccine. The analysis suggested that a single dose of the Pfizer-BioNTech vaccine offered only about 33% protection against symptomatic disease.

This was a reduction from the previous 50% effectiveness estimated against the alpha variant.

The study also found that the Pfizer-BioNTech vaccine was 88 percent effective against the delta variant 2 weeks after the second dose.

Study 2

A reportTrusted Source published in the journal Nature reflected the findings that a single shot of a two-dose vaccine such as Pfizer-BioNTech or AstraZeneca provided “barely” any protection.

However, researchers also reported that people who had received two doses of a vaccine had significantly more protection against infection with the delta variant, with researchers estimating a level of 95 percent effectiveness.

The study also found that the delta variant was less sensitive to “sera from naturally immunised individuals,” meaning people who had a prior infection may not be protected against reinfection with the delta variant.

Study 3

A study in Canada, meanwhile, found that two doses of a COVID-19 vaccine worked just as well against the delta variant as it did with alpha. It has not yet been peer reviewed.

The study suggested the Pfizer-BioNTech vaccine was around 87 percent effective 14 days after two doses.

Study 4

A study in ScotlandTrusted Source found similar results. The Pfizer-BioNTech vaccine, researchers concluded, offered “very good” protection against the delta variant and demonstrated 79 percent effectiveness 14 days after receiving the second dose.

Study 5

A study in Israel was more of an outlier and found that the Pfizer-BioNTech vaccine did not offer as high protection as previously estimated. The study suggested the vaccine was about 64 percent effective against preventing infection with the delta variant and 64 percent effective against symptomatic illness after two doses.

But scientists have pointed out that the full data has not yet been released, and it may have included asymptomatic infections picked up by Israel’s surveillance program.


Anywhere from 64 to 96 percent effective against the delta variant with two doses.

A third dose?

Pfizer and BioNTech say they’re now in the process of developing a third dose of their COVID-19 vaccine that will act as a booster against the delta variant. The companies said new data from the Israeli Ministry of Health, which showed that the vaccine’s effectiveness declines after 6 months, spurred them to launch the research.

Clinical trials for the booster vaccine could begin as early as August.

“Pfizer-BioNTech is seeking FDA approval for a booster to address waning antibody 6 months following full immunization, with particular concerns for protection against new variants,” Smith said.

However, Smith told Healthline that the currently available vaccines have been effective in preventing severe disease, including those identified with current variants of concern.

“Further, the CDC has not recommended a booster following any vaccine against SARS-CoV-2, as current data are limited,” she added.

The Moderna COVID-19 vaccine

There are multiple lab studies that suggest the Moderna COVID-19 vaccine works against the delta variant. And similar to the Pfizer-BioNTech vaccine, Moderna is also testing whether a third dose is beneficial.

Study 1

A lab study on the Moderna vaccine showed that the vaccine was capable of providing protection against the delta variant and other variants tested, even though it was much more reduced compared with the alpha variant.

But the most interesting finding was that the vaccine was far more effective in producing antibodies against delta than it was against beta, according to the data, which has not yet been peer reviewed.

“As we seek to defeat the pandemic, it is imperative that we are proactive as the virus evolves. [T]hese new data are encouraging and reinforce our belief that the Moderna COVID-19 vaccine should remain protective against newly detected variants,” Stéphane Bancel, CEO of Moderna, said in a statement.

No clear level of effectiveness was mentioned.

Study 2

The same Canadian study that found the Pfizer-BioNTech vaccine to be 87 percent effective suggested that the Moderna vaccine was 72 percent effective against the delta variant after one dose.

There wasn’t enough data to calculate protection after two doses for Moderna. It’s also important to point out that the study has not yet been peer reviewed.

The findings, however, indicate that even a single dose of the Moderna or Pfizer-BioNTech vaccines provides “good to excellent” protection against symptomatic infection as well as severe illness. Two doses were also found likely to provide even higher protection.


One study estimates 72 percent effectiveness from one dose. Other studies suggest it may offer similar protection as the Pfizer-BioNTech vaccine.

The Johnson & Johnson COVID-19 vaccine

There’s little data that shows how effective the Johnson & Johnson (J&J) single-shot COVID-19 vaccine is at protecting against the delta variant. The company is also reportedly researching whether a second shot would boost immunity against the variants.

Study 1

A recent clinical trial suggested that the vaccine was 85 percent effective against severe disease and demonstrated “strong, persistent” protection against hospitalisation and death.

It also showed that the J&J vaccine prompted “neutralizing antibody activity,” which stops the virus from infecting healthy cells, against the delta variant at a higher level than it did for the beta variant.

The Pfizer-BioNTech and AstraZeneca vaccines had shown a decline in effectiveness against the latter in another study.

Study 2

Interim results from a study involving 20 people has shown that the J&J vaccine neutralized the delta variant within 29 days of the first shot, and protection improved over time.

“Current data for the eight months studied so far show that the single-shot Johnson & Johnson COVID-19 vaccine generates a strong neutralising antibody response that does not wane; rather, we observe an improvement over time. In addition, we observe a persistent and particularly robust, durable cellular immune response,” said Dr. Mathai Mammen, the global head of Janssen Research & Development at Johnson & Johnson, in a July 1 press release.—

Disclaimer: The views expressed in this article do not represent those of the European Union or the International Media Support

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