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Healthcare workers prepare doses of Johnson & Johnson’s COVID-19 vaccine at a clinic targeting members of the immigrant community on March 25, 2021, in Los Angeles, CA. Mario Tama/Getty Images
  • Vaccines against COVID-19 were available to the public about 1 year after the pandemic began.
  • Three vaccines are currently in use in the United States: the Moderna, Pfizer-BioNTech, and Johnson & Johnson vaccines.
  • A new study shows that these vaccines are highly effective in preventing hospitalizations and emergency room (ER) visits.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

The COVID-19 pandemic continues to influence hospital systems all over the world. The Centers for Disease Control and Prevention (CDC) are continuing to try to track the number of cases of COVID-19 and the deaths resulting from it in the U.S.

In the U.S., there have been more than 41 million cases of COVID-19 and in excess of 660,000 related deaths.

Since vaccines against COVID-19 became available, experts have been researching their overall effectiveness in preventing severe cases of COVID-19.

This research includes looking at hospitalization rates and ER visits among individuals who have received vaccination against COVID-19.

A recent study, which appears in the New England Journal of Medicine, suggests that full mRNA vaccination — two doses — against COVID-19 is 89% effective in preventing hospitalizations related to the disease.

Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.

Scientists started developing vaccines against SARS-CoV-2, the virus that causes COVID-19, shortly after the start of the pandemic. However, researchers had been investigating vaccines for coronaviruses in general for years before this.

The Food and Drug Administration (FDA) approved the Pfizer-BioNTech vaccine, also called BNT162b2, for emergency use in December of 2020. The Moderna vaccine, also called mRNA-1273, received similar authorization around the same time. These are both mRNA vaccines, and both require two shots for full vaccination.

In addition to these, there is also Johnson & Johnson’s Janssen vaccine, or the Ad26.COV2.S vaccine, which is a single dose vaccine.

Currently, about 75% of the U.S. population have received at least one vaccine dose. Research is ongoing regarding vaccine effectiveness in minimizing the severity of SARS-CoV-2 infections.

As the authors explain, placebo-controlled phase 3 trials of these three vaccines and observational studies of the mRNA vaccines have already demonstrated that they are “highly effective in preventing symptomatic COVID-19.”

However, the authors also write that “less is known about how well these vaccines protect against more severe illness due to [SARS-CoV-2] resulting in hospitalization, admission to an intensive care unit (ICU), or ambulatory care in an emergency department or urgent care clinic.”

To investigate, the current study investigated the effectiveness of vaccines in preventing severe symptoms of COVID-19. Specifically, they examined:

  • hospitalizations
  • stays in ICUs
  • ER or urgent care clinic visits

The researchers collected data from January 1 through June 22, 2021, from 187 hospitals in multiple states. The study included adults aged 50 years and older. The researchers’ data included 41,552 hospital admissions and 21,522 visits to either ERs or urgent care clinics.

The data also included the vaccination status of the participants, including the number of doses and how long it had been since they received their doses.

The researchers accounted for the age of each participant, as well as their geographic region, the time frame of vaccination and, the local circulation of the virus. They used this information to assess the effectiveness of COVID-19 vaccines.

Discussing their methods, the authors write, “We used a test-negative design to estimate vaccine effectiveness by comparing the odds of a positive test for SARS-CoV-2 infection among vaccinated patients with those among unvaccinated patients.”

Their results showed that the vaccines were highly effective in preventing hospitalizations, stays in the ICU, and ER visits related to COVID-19. The results included the following highlights:

  • The mRNA vaccines — Moderna and Pfizer–BioNTech — were 89% effective in preventing hospitalization in confirmed positive cases of a SARS-CoV-2 infection.
  • Both Moderna and Pfizer–BioNTech were 90% effective in preventing ICU admissions and 91% effective in preventing ER or urgent care visits.
  • The Johnson & Johnson vaccine was 68% effective in preventing hospitalization and 73% effective in preventing ER or urgent care visits.

The researchers also found that vaccines were highly effective among groups whom the virus disproportionately affects, including people aged 85 years or older, Black and Hispanic adults, and individuals with chronic respiratory diseases.

Study author Dr. Shaun Grannis told Medical News Today that this study and other research represent “our initial efforts using real world data from actual patients to develop a solid evidence base for the effectiveness of COVID-19 vaccines.” He continued:

“Evidence of this nature is crucial to understanding the impact of the vaccines on the pandemic and to providing information to public health experts and people who are unsure about receiving the vaccine.”

The study, which the CDC supported, did have some limitations. The authors note the potential for bias and acknowledge that their analysis could not account for all influential factors.

For example, they did not take into account exposure risk based on factors such as profession. Some professions had access to vaccinations and personal protective equipment, whereas others did not.

However, they attempted to account for this by not beginning data collection until the vaccines were available to the general public.

Also, they took data from several different hospitals and clinical settings. The researchers note that the policies for testing for SARS-CoV-2 may vary among hospitals based on vaccination status. There was a risk of both over and underestimation of vaccine efficiency.

Importantly, based on the time frame of the study, the researchers were not able to determine vaccine efficacy against the delta variant.

Moving forward, Dr. Grannis emphasized a few areas of continued interest. He told MNT:

“It will be important to evaluate additional dimensions, including the impact of previous [SARS-CoV-2] infection on vaccine effectiveness, effectiveness among younger populations, waning immunity, and effectiveness for the immune suppressed, among other topics.”

In response to being asked to comment on the study, Dr. David W. Dowdy, an epidemiology specialist with Johns Hopkins University, was eager about the study’s results. He told MNT:

“[The study] provides robust scientific evidence that the vaccines in use in the U.S. — and particularly the Pfizer and Moderna vaccines — provide strong, consistent protection again SARS-CoV-2 infection that is serious enough to seek care in an urgent care or an emergency department.”

“In every population the authors tested, full vaccination provided [greater than] 80% protection — regardless of age, race, geographic location, or other medical conditions,” he continued.

He further emphasized that continued research could focus efforts on investigating the waning immunity of COVID-19 vaccines:

“There was also no evidence of waning immunity, but this paper was only able to look at the first ~4 months after getting the final dose of the vaccine. So I don’t think we can use this as evidence for or against waning of immunity beyond that time.”

Overall, this study represents continued efforts in data collection regarding vaccines for COVID-19. It demonstrates high levels of vaccine effectiveness, particularly among those whom the SARS-CoV-2 virus is most likely to affect.

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