[Healthline] How the COVID-19 vaccine works against the Delta variant.


The Delta variant – which has been on the rise since July, now accounts for more than 99% of all new coronavirus infections in the US.

Hospitalizations have increased in recent months. The majority involve unvaccinated people.

Although the vaccine’s effectiveness has been slightly reduced against the Delta variant, the data to date suggest that the Moderna vaccine is about 50 to 95 percent effective against Delta and the Pfizer vaccine. -BioNTech is 39 to 96 percent efficient for Delta.

Although vaccines offer varying degrees of protection, international reviews suggest they still provide strong protection against hospitalization at 60 to 95 percent.

After the first COVID-19 case with the Delta variant was confirmed in the United States in May of this year, the variant is now the only dominant variant in the country, accounting for more than 99% of all coronavirus infections. new in the country.

The highly infectious variant was first identified in India in December. Like previous variants, it quickly spread to many countries around the world, most notably the UK. Great Britain.

COVID-19 cases are rapidly increasing again in the United States. The average daily number of COVID-19 cases is more than 145,000, according to data from the Centers for Disease Control and Prevention (CDC).

What do we know about the Delta variant?

Research has suggested that the Delta variant is estimated to be 60 percent more contagious than the Alpha variant, which could explain the rapid increase in cases in recent months.

A CDC report says the Delta variant is much more contagious than the common cold, the 1918 Spanish flu pandemic, and severe acute respiratory syndrome (SARS), and can be transmitted similarly to chicken pot.

A study from the Chinese Academy of Medical Sciences also found that Delta’s viral load was approximately 1,000 times higher than those caused by previous coronavirus variants.

In addition to being more infectious, the Delta variant can also be more deadly,

A study out of Scotland found that the Delta variant was twice as likely to lead to hospitalization.

In addition, Public Health England confirmed that among unvaccinated people, the Delta variant would double the risk of hospitalization compared with the Alpha variant.

Vaccine – Delta variant

Since the Delta variant appeared, scientists have been trying to determine if the current COVID-19 vaccine is effective against it.

Immunity can decline over time, and newer infectious variants emerge that could affect the effectiveness of the vaccine, scientists say.

However, according to the latest research released by the CDC, people who are not vaccinated are 10 times more likely to be hospitalized with COVID-19 than those who have been vaccinated.

Research shows that unvaccinated people are also 11 times more likely to die from COVID-19 than those who have been vaccinated.

Pfizer-BioNTech COVID-19 Vaccine

Due to limited research, trying to determine the effectiveness of each vaccine against the Delta variant has so far been a challenge. However, there have been highly reliable results as follows:

Alpha – Delta

Research in Scotland, the United States and Qatar found that the Pfizer-BioNTech vaccine provides 80 to 100 percent protection against any infection with the Alpha variant.

Studies in Canada, Scotland and the United Kingdom show that the vaccine also provides the same range of protection for infected patients who are symptomatic.

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British and Qatari researchers found that the vaccine was more than 90 percent effective against severe disease with the Alpha variant.

However, similar studies have noted a slight reduction in effectiveness, about 80%, against infection with the Delta variant.

The Qatar study recorded a larger reduction, about 60 percent. But the vaccine’s effectiveness is still higher or close to 90% for hospitalizations and severe illness.

The Israeli data also showed that the effectiveness of the Pfizer-BioNTech vaccine against infection fell to 39% between June and July, down from 64% previously.

These findings contradict UK data showing it is 88% effective against symptomatic infections caused by Delta.


The vaccine’s effectiveness has been 87 to 96% against all variants since before the Delta strain, but now it is 39 to 84% effective against infection and 75 to 95% effective in reducing hospitalization rates.

Moderna COVID-19 vaccine

Alpha – Delta

A study by the Mayo Clinic found that the vaccine’s effectiveness against symptomatic infection with the Delta variant dropped from 86% to about 76% in July.

The vaccine’s effectiveness against COVID-19-related hospitalizations also decreased from more than 90% in the Alpha variant to about 81% with the Delta variant.

A Canadian study found that a single dose of Moderna vaccine was 83% effective in patients with symptomatic infections caused by the Alpha variant. This number increases to 92 percent with two full doses.

However, the effectiveness decreased to 72 percent for the Delta variant when injected with only one dose.

Johnson & Johnson COVID-19

A clinical trial found the vaccine to be 85% effective for severe disease. In research, it demonstrated “strong, persistent” protection against hospitalization and death.

Another study, which examined only 27 people, found the J&J vaccine to be 67% effective against the Delta variant.

The study also showed that the vaccine produced fewer antibodies against Delta than the Alpha variant, but the scientists say it may not accurately reflect the actual performance of the vaccine.

The most recent findings, and the only real data, come from South Africa, showing that the vaccine provides about 71% protection against hospitalization for Delta variant infection.


Like other vaccines, the J&J vaccine shows a slight decrease in effectiveness against the Delta variant, but more comprehensive studies are needed to provide a definitive answer.

Let’s analyze vaccine performance together

Pfizer-BioNTech or Moderna

A small laboratory study conducted by researchers in New York found that both the mRNA vaccines, Pfizer-BioNTech and Moderna, were 94 to 95% effective at preventing COVID-19 with Delta variant.

The HEROES-RECOVERN studies among US healthcare workers found that the Pfizer-BioNTech and Moderna vaccines are about 90% effective in preventing both symptomatic and asymptomatic coronavirus infections before mutating. Delta spread nationwide.

When Delta becomes dominant, efficiency drops to an estimated 66%, but the researchers also suggest that this could be a sign that protection fades over time.

Pfizer vs. Moderna

Using data from the Office of National Statistics (ONS) COVID-19 Infection Survey, Oxford researchers compared the Pfizer-BioNTech, Moderna and AstraZeneca vaccines to the Delta variant.

They found that a single dose of Moderna vaccine was as effective or more effective than other vaccines when given with the same dose.

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However, the researchers say this may be because people who get the Moderna vaccine are younger, and this vaccine more effective in young people.

An earlier study also showed that the Moderna vaccine reduces the risk of infection by two times compared with the Pfizer-BioNTech vaccine.

A study in nursing home residents observed that the anti-infection efficacy of the Pfizer-BioNTech vaccine was 74.2% with pre-Delta variants, and this number dropped to 52.4%. when infected with Delta .

In comparison, similar rates are 74.7 percent and 50.6 percent for Moderna.

Pfizer-BioNTech, Moderna or J&J

The COVID-NET studies found that these three vaccines were 80 to 90 percent effective in reducing hospitalizations for Delta strains in people 75 years of age and older by July. It was slightly reduced. compared to more than 90% in previous months.

CDC analyzed the performance of three vaccines against the Delta variant and found them to be 86% effective in preventing hospitalization and 82% effective in preventing severe illness and providing emergency treatment. .

The researchers also found that the Moderna vaccine provided the most significant protection in preventing hospitalization at 95%.

Pfizer-BioNTech is 80% effective in preventing hospitalization and the J&J vaccine is about 60% effective in preventing hospitalization.


The three vaccines currently in use in the United States are 39 to 84% effective in preventing infection. According to CDC provided.

Third dose of COVID-19 vaccine to boost protection

Israel became the first country to widely roll out additional doses of the COVID-19 vaccine to people at higher risk of contracting the disease. Currently, people 60 years of age and older can get a third dose of the Pfizer-BioNTech vaccine as a booster.

Israel’s Health Ministry says its decision is based on national health statistics, which show that people vaccinated in April seem to have 75% protection from infection, while protection for those vaccinated in January dropped to 16%.

Dr Venky Soundararajan, who led the aforementioned Mayo Clinic study, said a Moderna booster shot is also being worked on. It may be recommended for people who received the Pfizer-BioNTech or Moderna vaccine earlier this year.

Other countries, such as the United Kingdom, Spain and Germany, have also approved a third dose for people who have not achieved an appropriate immune response after the initial two doses.

The United States is also one of them

The CDC has so far only recommended a three-shot regimen to increase protection for immunocompromised individuals, such as organ transplant recipients and people with cancer.

The US also has a booster plan that will give people an injection of Pfizer-BioNTech or Moderna 8 months after their second dose. The rollout is expected to begin on September 20.

However, after Moderna claimed its booster dose was half the dose of the original injections, the FDA said it needed more time and evidence before making a decision.

Moderna also said on September 9 that it is working on a single vaccine that combines both a COVID-19 booster dose and a flu shot.

FDA officials will objectively debate Pfizer-BioNTech’s evidence to see which groups would be recommended for use as a COVID-19 booster.

Source: https://www.healthline.com/health-news/here-how-well-covid-19-vaccines-work-against-the-delta-variant

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