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COVID-19 vaccines continue to protect the population against severe disease and death. EMILY KASK/AFP via Getty Images
  • The Delta variant of COVID-19 is causing surges in cases across the United States, and because vaccination coverage is uneven within the states, there is higher transmission.
  • New COVID-19 cases and hospitalizations continue to be largely limited to the unvaccinated, and only a small percentage of vaccinated people experience breakthrough infections.
  • Despite some reports indicating reduced vaccine efficacy against symptomatic COVID-19 infection with the Delta variant, real-life data shows the three available vaccines offer great protection against hospitalization and death.
  • The CDC recommends everyone over 12 years old who is eligible to get vaccinated.

New COVID-19 infections, hospitalizations, and deaths continue to increase across the United States, particularly in areas with higher rates of community transmission and lower vaccination coverage.

The southern United States, particularly Arkansas, Mississippi, Florida, and Alabama, have been battling new clusters of COVID-19 outbreaks. Hospitals have said they run the risk of being overwhelmed with patients and may not have the capacity to deal with them all.

Of those hospitalized, an increasing number are children, most of whom remain unvaccinated.

However, recent data appears to suggest waning effectiveness of the Pfizer-BioNTech vaccine against COVID-19 infection versus Moderna. This has increased worries about vaccines.

But how are vaccines really doing? Are they preventing enough hospitalizations and deaths related to COVID-19 as claimed?

Here is what the numbers say:

The numbers of COVID-19 cases and hospitalizations in the United States are rising by the day amid the rise of the more infectious Delta variant.

The 7-day average of new COVID-19 cases in all populations in the United States was 128,347, according to the Centers for Disease Control and Prevention (CDC).

A month ago, the average number was just over 33,000 cases, according to the CDC.

This surge in cases has also strained hospitals and healthcare professionals.

At least 80 percent of intensive care unit (ICU) beds in Arkansas were occupied last week, while on August 17, the Alabama Hospital Association reported that the state had no ICU beds left.

More than 168 million Americans have been fully vaccinated against COVID-19, and just a small fraction have had breakthrough cases that led to hospitalization.

According to analyses conducted by the Kaiser Family Foundation (KFF) based on data from the Johns Hopkins University COVID-19 Dashboard and the U.S. Department of Health & Human Services, vaccines continue to protect people from severe disease and death due to COVID-19.

The vast majority of people who have died from COVID-19 were unvaccinated. Fatal cases of COVID-19 among vaccinated people are either very low or virtually zero in 48 states.

Small number of breakthrough cases

In all states, the rate of breakthrough cases among the fully vaccinated is below 1 percent.

Connecticut, for example, has one of the lowest breakthrough rates at 0.01 percent. Over 64 percent of people have been fully vaccinated in the state.

In Arizona, 94.1 percent of new COVID-19 cases involve unvaccinated people.

Even in Tennessee, where vaccination coverage is at 41 percent, fully vaccinated people who acquired the coronavirus is only 0.4 percent.


The number of fully vaccinated people who were hospitalized was only 8,054 as of August, according to the CDC. This is a tiny fraction of the 168 million people who have been fully vaccinated.

A significant portion of these hospitalized cases, 17 percent, were among people who showed no symptoms of COVID-19 and were classed as asymptomatic. They may have been hospitalized for a different condition and then found to have had COVID-19.

The rate of hospitalization among fully vaccinated people with COVID-19 was effectively zero in recent weeks in California, Delaware, D.C., Indiana, New Jersey, New Mexico, Vermont, and Virginia.

It was 0.06 percent in Arkansas, meaning over 99 percent of hospitalizations were unvaccinated.

Over 95 percent of those hospitalized in Alaska and 99.93 percent in New Jersey were not yet fully vaccinated either.

Vermont, which has 67 percent of its population fully vaccinated, shared similar statistics, with 13 people being hospitalized out of 276 people.

In one study from the Kaiser Family Foundation, unvaccinated people made up more than 9 in 10 people who were hospitalized or died due to COVID-19.


Of the 8,054 hospitalized breakthrough COVID-19 cases, at least 1,587 deaths are known to have occurred. This is still a tiny fraction of the 168 million people who are vaccinated in the United States.

Over 96 percent of people who died in Montana and 99.91 percent in New Jersey were not fully vaccinated.

If we look at the number of vaccinated people developing COVID-19, the District of Columbia is another good example to examine. Of 200 fully vaccinated people who acquired SARS-CoV-2, only 13 were hospitalized, and none died.

However, as the Delta variant has surged, health officials have seen an increase in symptomatic COVID-19 cases in people with vaccines, even though they remained highly protected against severe symptoms.

On August 18, the CDC announced that COVID-19 booster shots would be available to people who have had an mRNA vaccine in at least the past 8 months. The decision was made after the Delta variant was able to cause more breakthrough COVID-19 cases in recent months.

Booster shots are also expected to be made available to people who got the Johnson & Johnson vaccine, but researchers are waiting for more data.

A study, conducted by Mayo Clinic and Cambridge-based biotech company nference and posted in preprint MedRxiv last week, suggested that the Moderna vaccine’s effectiveness against the Delta variant fell to 76 percent and Pfizer’s dropped to 42 percent.

Ravina Kullar, PharmD, infectious diseases expert and epidemiologist based in Los Angeles, told Healthline that the results from the Mayo Clinic study need to be evaluated in relation to other published peer-reviewed data.

“Interestingly, in this observational study, which has yet to be peer-reviewed, Pfizer’s vaccine efficacy was shown to decrease from 76 percent in January to 42 percent in July when the Delta variant became the dominant variant in the U.S.,” she said.

Kullar said a major limitation to this study was that the authors assumed that patients in July had the Delta variant.

“This was not verified via sequencing. Additionally, the 42 percent is based on one month’s worth of data. These results differ from findings published in the New England Journal of Medicine last month revealing that two doses of the Pfizer vaccine provide 88 percent protection against Delta and data from England’s Public Health department in May that reported the same level of protection,” she said.

Experts agree that the current vaccines are continuing to provide durable protection against severe disease and death.

“Pfizer-BioNTech reported an efficacy of 95 percent for their COVID-19 vaccine. This means a 95 percent reduction in new cases of the disease in the vaccinated group compared with the placebo group,” said Donald J. Alcendor, PhD, assistant professor of cancer biology at Vanderbilt University School of Medicine.

The real-world effectiveness of the three currently authorized COVID-19 vaccines in the United States paints a positive picture.

Between Feb. 1 and April 30, 2021, 7,280 patients ages 65+ from the COVID-19–Associated Hospitalization Surveillance Network (COVID-NET) were analyzed with vaccination coverage data from state immunization information systems.

Of these patients, 5,451 (75%) were unvaccinated, 867 (12%) were partially vaccinated, and 394 (5%) were fully vaccinated.

When comparing vaccine effectiveness in the fully versus partially vaccinated, COVID-NET found the following figures:

  • For adults ages 65–74 years, the effectiveness of full vaccination against hospitalization with COVID-19 was 96% for Pfizer-BioNTech, 96% for Moderna, and 84% for the Johnson & Johnson (J&J) vaccine.
  • For those ages 75+, the Pfizer vaccine provided 91% protection, Moderna 96%, and J&J 85%.
  • The effectiveness of partial vaccination in those ages 75 and over was 66% for Pfizer and 82% for Moderna.

These figures prove that the vaccines retain a high level of effectiveness in preventing COVID-19-associated hospitalization in older adults.

However, this data was taken before the Delta variant became widespread in the United States.

When interpreting data about vaccines…

Kullar says it is important to look at all of the data published rather than a single study. It is also crucial to look at the patient population evaluated, the duration of the study, and the case definitions used.

When discussing efficacy, scientists speak of data from clinical trials, while effectiveness is measured from real-world data, says Dr. Eyal Leshem.

“Vaccine efficacy is the percentage reduction in disease in a group of people who have received the vaccine in a clinical trial. It differs from vaccine effectiveness, which measures how well a vaccine works when given to people in the community outside of clinical trials,” Alcendor says.

Was this helpful?

Alcendor told Healthline that it is natural to see antibody levels decrease over time for vaccines.

He said this reduction varies according to the individual, influenced by age, sex, and genetics, as well as the antigen in the vaccine formulation.

This is the very reason why boosters are administered for some scheduled vaccines such as hepatitis A, hepatitis B, Haemophilus influenza type B (Hib), measles-mumps-rubella (MMR) tetanus, diphtheria, and pertussis (Tdap), and varicella, he added.

The Food and Drug Administration (FDA) recently approved COVID-19 booster shots for individuals with weakened immune systems, who are more likely to have a poor immune response to the vaccine and have lower protection.

The CDC announced that booster shots would also be available to the general population this fall, pending approval by the FDA.

Touching on recent data suggesting a waning in antibody levels, Alcendor said this does not mean the vaccine suddenly stops working.

“When we observed reduced antibody levels, we still don’t know what antibody levels are needed to be protective against the Delta variant. It could be that your antibody level has gone down but not below the level of protection against the variant.”

Alcendor acknowledged that the number of such breakthroughs has increased since the Delta variant of SARS-CoV-2 became the dominant strain in many parts of the world.

Among factors that contribute to breakthrough infections are “poor immune response to the vaccines due to advanced age and underlying comorbidities, waning immune protection from the vaccines over time, and viral variants that escape existing immune protection from the vaccines,” he said.

Data from Israel showed less than anticipated protection against the Delta variant in people who had the Pfizer vaccine. This data also influenced decisions by the FDA and CDC about the need for boosters.

“We are experiencing similar trends in Israel with reductions in Pfizer vaccine effectiveness against Delta variant infections. We consider both the higher infectiousness of Delta and declining antibody levels the reasons for the reductions in vaccine effectiveness,” said Dr. Eyal Leshem, director of the Center for Travel Medicine and Tropical Diseases at Sheba Medical Center and clinical associate professor at the Tel Aviv University School of Medicine.

But, he added: “Most data still show very high vaccine effectiveness against severe disease and hospitalization for both the Pfizer and Moderna vaccines.”

Israel is currently offering a third dose of COVID-19 vaccines to those over 50 years old. Leshem told Healthline that behind that decision was also the record number of cases and hospitalization since March 2021.

“We think that while the vaccine maintains most of its effectiveness against severe disease, its effectiveness in preventing infection declines, which is one of the reasons we recommended booster doses.”

The COVID-19 vaccines were developed to stop developing severe forms of the disease that can lead to hospitalization and death. In that aspect, they have been extremely successful even if the vaccines are not 100 percent effective.

While it is true that some partially and fully vaccinated people have developed COVID-19, breakthrough infections should not be a concern for most of the population. Doctors, however, do still recommend people exercise caution in areas with low vaccination rates and high transmission.

Vaccines also greatly reduce the likelihood of mild and symptomatic infections as well as prevent death and hospitalization.

Kullar noted that the Delta variant is both more contagious and transmissible, and those who are harboring the Delta variant can carry as much as a 1,200 times higher viral load than the original strain.

“Given all of this information, it is important for everyone not only to get fully vaccinated but also follow infection prevention measures, such as wearing a face mask in the public, physically distancing from others, and avoiding large crowds until we round the turn of this surge.”