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  • Coronavirus infections caused by the Delta variant, which has surged since July, now make up more than 99 percent of all new coronavirus infections in the United States.
  • There’s been an increase in hospitalizations in recent months. The majority involve unvaccinated people.
  • Although vaccine effectiveness has waned slightly against infection with Delta, data so far suggests the Moderna vaccine is approximately 50 to 95 percent effective against Delta, and the Pfizer-BioNTech vaccine is 39 to 96 percent effective against Delta.
  • Even though vaccines offer different ranges of protection, real-world evaluations show they still provide robust 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 this year, the variant is now the sole dominating variant nationwide, making up more than 99 percent of all new coronavirus infections in the country.

The highly infectious variant was first identified in India in December. As with previous variants, it quickly spread to many countries across the world, including, most notably, the United Kingdom.

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

Research has suggested that the Delta variant is an estimated 60 percent more transmissible than the Alpha variant, which could explain the rapid rise in cases in recent months.

A leaked CDC internal report said the Delta variant was much more contagious than the common cold, the 1918 Spanish flu, and severe acute respiratory syndrome (SARS), and may be as transmissible as chickenpox.

A preprint study from the Chinese Academy of Medical Sciences also found that viral loads of Delta infections are approximately 1,000 times higher than those caused by previous coronavirus variants.

Apart from being more infectious, the Delta variant could also be more deadly, several studies suggest.

A study in Scotland found the Delta variant was twice as likely to lead to hospitalization.

Additionally, a cohort study by Public Health England confirmed that among unvaccinated people, the Delta variant more than doubled the risk of hospitalization than the Alpha variant.

People also became more acutely ill with Delta-driven infections.

Areas with low vaccination rates in the United States have been seeing more significant surges in infections.

The latest situation in hot spots such as Arkansas, Florida, and Texas attests to this.

Hospitals in these states have announced critical shortages of oxygen supplies, and have said they’re fast approaching intensive care unit (ICU) capacity limits.

Since the Delta variant emerged, scientists have been trying to establish whether the current COVID-19 vaccines are as effective against it.

Recent studies show there’s been a slight decrease in observed effectiveness since March, when the Delta variant only made up 7 percent of COVID-19 cases in the United States.

By the time July rolled around, this figure skyrocketed to 94 percent.

Scientists say immunity may wane over time and new more infectious variants in a population may affect vaccine effectiveness, among many other factors.

However, according to the latest study released by the CDC, unvaccinated people are over 10 times more likely to be hospitalized with COVID-19 than vaccinated people.

Unvaccinated people are also 11 times more likely to die of COVID-19 than vaccinated people, the study found.

We broke down what the current data says. 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.

Alpha versus Delta

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

Studies in Canada, Scotland, and the United Kingdom suggest the vaccine offers the same range of protection for symptomatic infection as well.

As for protection against hospitalization, British and Qatari researchers found the vaccine was more than 90 percent effective against severe disease with the Alpha variant.

However, the same studies noted a slight drop in effectiveness, to around 80 percent, against any infection with the Delta variant.

The Qatar study recorded a bigger drop to about 60 percent. But the vaccine’s effectiveness remained above or close to 90 percent for hospitalization and severe disease.

Israeli data has also suggested that the Pfizer-BioNTech vaccine’s effectiveness against infection dipped to as low as 39 percent between June and July, down from the previous 64 percent.

These findings conflicted with U.K. data that found it to be 88 percent effective against symptomatic infection caused by Delta.

Estimated effectiveness of Pfizer-BioNTech vaccine

Vaccine effectiveness was 87 to 96 percent for all outcomes before Delta, but now it’s 39 to 84 percent effective against infection and 75 to 95 percent effective against hospitalization.

The Moderna COVID-19 vaccine

Many lab studies and real-life data suggest the Moderna COVID-19 vaccine works against the Delta variant.

Alpha versus Delta

A preprint Mayo Clinic study suggests that the vaccine’s effectiveness against symptomatic infection with the Delta variant dropped from 86 percent to around 76 percent in July.

The vaccine’s effectiveness against COVID-19-associated hospitalization also decreased from over 90 percent when the Alpha variant was dominant to around 81 percent with Delta.

A preprint Canadian study found that one dose of the Moderna vaccine was 83 percent effective against symptomatic infection caused by the Alpha variant. This increased to 92 percent with both doses.

However, effectiveness decreased to 72 percent for the Delta variant with one dose. The study could not reliably estimate protection with two doses.

Estimated effectiveness of Moderna COVID-19 vaccine

Vaccine effectiveness was around 80 to 95 percent for all outcomes before Delta, but now it’s 50 to 72 percent effective against infection and over 80 percent effective against hospitalization.

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.

Alpha versus Delta

A clinical trial suggests the vaccine is 85 percent effective against severe disease. In the study, it demonstrated “strong, persistent” protection against hospitalization and death.

Another study, which has not yet been peer-reviewed and only examined 27 people, suggests the J&J vaccine is 67 percent effective against the Delta variant.

The study also found the vaccine produced fewer antibodies against Delta than it did for the Alpha variant, but scientists say it may not accurately reflect the vaccine’s real-life performance.

The most recent findings, and the only real-life data, are from South Africa, which suggests that the vaccine offers about 71 percent protection against hospitalization when the Delta variant dominates.

Estimated effectiveness of J&J COVID-19 vaccine

As with other vaccines, the J&J vaccine shows a slight dip in effectiveness against the Delta variant, but more comprehensive studies are needed to reach a definitive answer.

Pfizer-BioNTech or Moderna

A small, preprint laboratory study carried out by New York researchers suggests that both mRNA vaccines, Pfizer-BioNTech and Moderna, are 94 to 95 percent effective in preventing COVID-19 with the Delta variant.

The HEROES-RECOVER cohort study among U.S. healthcare workers found that the Pfizer-BioNTech and Moderna vaccines were about 90 percent effective in preventing both symptomatic and asymptomatic infection with the coronavirus before the Delta variant spread across the country.

When Delta became predominant in the summer, effectiveness fell to an estimated 66 percent, but researchers also think this may be a sign that protection wanes over time.

Pfizer vs. Moderna

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

They found that a single dose of the Moderna vaccine had similar or greater effectiveness than a single dose of the others.

However, researchers said this could be because people receiving the Moderna vaccine were younger on average, and the vaccine has greater effectiveness in younger people.

A preprint study also suggests that the Moderna vaccine reduces the risk of breakthrough infection twofold than the Pfizer-BioNTech vaccine.

One study that observed nursing home residents found that the Pfizer-BioNTech vaccine’s effectiveness against infection was 74.2 percent before Delta, and this dropped to 52.4 percent when Delta dominated.

Comparatively, the same rates were 74.7 percent and 50.6 percent for Moderna.

Pfizer-BioNTech, Moderna, or J&J

The COVID-NET study found that these three vaccines were between 80 and 90 percent effective against hospitalization with the Delta variant in people 75 and older in July. This was a slight drop from over 90 percent in the previous months.

A separate study that analyzed all adults in New York state found that vaccine effectiveness against infection declined from around 91.7 percent to 79.8 percent from May to July when the Delta variant spread.

An early release CDC study analyzing the performance of the three vaccines against the Delta variant suggests they’re 86 percent effective at preventing hospitalization and 82 percent effective at preventing severe outcomes and urgent care.

Researchers also found that the Moderna vaccine offered the most significant protection at preventing hospitalizations at 95 percent.

Pfizer-BioNTech was 80 percent effective at preventing hospitalization, and the J&J vaccine was about 60 percent effective at preventing hospitalization.

Overall estimated effectiveness of COVID-19 vaccines

The three vaccines in use in the United States are 39 to 84 percent effective at preventing infection. Effectiveness against hospitalization is approximately between 60 and 95 percent since the Delta variant became dominant, according to the CDC.

Israel became the first country to widely administer an additional dose of COVID-19 vaccine for people at higher risk. Currently, people 60 or older can get a third dose of the Pfizer-BioNTech vaccine as a booster.

The Israeli Health Ministry said its decision was based on national health statistics, which suggested that people vaccinated in April appeared to have 75 percent protection against infection, while protection for people vaccinated in January dropped to as low as 16 percent.

Venky Soundararajan, PhD, who led the abovementioned Mayo Clinic study, said a Moderna booster shot is also in the works. It may be recommended for people who got the Pfizer-BioNTech or Moderna vaccines earlier this year.

Other countries, such as the United Kingdom, Spain, and Germany, have also approved third doses to be administered to people who do not mount a proper immune response after getting their initial two doses.

The United States is also one of them.

The CDC has so far only recommended a three-shot regimen to boost protection for immunocompromised people, such as organ transplant recipients and people with cancer, who received either the Pfizer-BioNTech or Moderna vaccine.

The United States also has a booster plan that would offer people either Pfizer-BioNTech or Moderna boosters 8 months after their second dose. The rollout is expected to start Sept. 20.

However, after Moderna requested that its booster be half the dose of the original shots, the FDA said it needs more time and evidence before it makes a decision.

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

FDA officials will publicly debate Pfizer-BioNTech’s evidence to see which groups will be recommended a COVID-19 booster.

J&J is also considering a second shot of its vaccine to be used as a booster and will submit an application to the FDA.

The Pfizer-BioNTech, Moderna, and J&J vaccines are proven to be effective in varying degrees against the original variant of the coronavirus that causes COVID-19.

Vaccination programs and studies are showing that the vaccines work against the Delta variant, too.

“We [know] that our authorized vaccines prevent severe disease, hospitalization, and death from the Delta variant,” CDC Director Dr. Rochelle Walensky said.

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

Research has also solidified the importance of getting fully vaccinated despite a perceived reduction in effectiveness against symptomatic or asymptomatic infection with the Delta variant since July.

A recent study suggests that fully vaccinated people are two times less likely to have no COVID-19 symptoms if they contract an infection. The likelihood of hospitalization also dropped by two-thirds after receiving two doses.

Although the exact duration of protection offered by vaccines still remains unknown, real-world evaluations suggest that they are at least 84 percent effective against hospitalization 24 weeks after the second dose.

Breakthrough infections can be expected

Although we’re seeing more breakthrough cases in vaccinated people, and studies indicate that vaccine effectiveness against infection is waning slightly over time, protection against severe disease or death remains strong.

Experts stress that vaccines are highly protective, even if they’re not 100-percent effective.

A preprint study that analyzed 161 vaccine breakthrough infections among 24,706 vaccinated healthcare workers found that although vaccinated people who contract the coronavirus have similar levels of the virus in their noses and throats as unvaccinated people, not all of it is as infectious.

The breakthrough cases presented with mild or asymptomatic infections, of which more than 90 percent were attributed to the Delta variant.

Additionally other experiments also showed that the viral shedding from vaccinated people was lower. Researchers hypothesized this was because some of the virus had already been neutralized by antibodies produced from the vaccine.

The World Health Organization (WHO) has said data so far supports claims that the Pfizer-BioNTech work against preventing severe COVID-19 caused by the Delta variant.

But it has also acknowledged that the vaccines may offer less protection against milder, symptomatic illness caused by Delta, though studies still suggest that people fully vaccinated retain significant protection against Delta.

Receiving the full regimen of two doses of an mRNA COVID-19 vaccine, such as the Pfizer-BioNTech or Moderna vaccine, has also shown to be much more effective against the Delta variant.

“The bottom line is that the vaccination program with any of the current vaccines available is the only way to break the cycle of spread by not allowing the virus to infect unvaccinated hosts and then mutate into variants such as delta. These vaccines are safe and with a high degree of efficacy to prevent further morbidities and mortalities,” Strange told Healthline.

Prof. Tim Spector, an epidemiologist from King’s College London, told Healthline that it was time for the United States to take lessons from the United Kingdom in dealing with the Delta variant.

“[They] should start spreading the word about the new symptoms. [D]o not get too relaxed when you get your vaccine either, especially if you are in a high-risk area.”
– Prof. Tim Spector, epidemiologist

“Your risk may be an eighth of what it was [after getting vaccinated], but still a considerable number of people will be infected,” he added, highlighting the importance of physical distancing and wearing masks in crowded, poorly ventilated places.