Pfizer and Moderna are 94% Effective, Says Real-World Study


According to a study by the CDC, Moderna and Pfizer vaccines are 94% effective at preventing hospitalizations in older adults.

Recently, the US Centers for Disease Control and Infection (CDC) assessed the effectiveness of Pfizer and Moderna vaccines at preventing hospitalizations in older adults. Older adults are at a greater risk for developing severe infection; therefore, monitoring the effectiveness of vaccines at preventing severe disease outcomes is a high priority.

The real-world study collected data from 417 adults aged 65 years and above who had undergone hospitalization between January and March 2021. All of whom had experienced COVID like symptoms. The researchers looked at hospitalizations in 24 hospitals across 14 states; including Michigan, Colorado, New York, California, and Texas. Those who tested positive for SARS-CoV-2 upon admission became case-patients, whereas those who tested negative became part of the control group. A total of 187 patients tested positive for coronavirus, and 230 tested negative.

Results showed that only one person, part of the group that tested positive, had received complete doses of a vaccine. Moreover, about 10% had received a single dose of either Pfizer or Moderna. In the control group, those who tested negative, 8% of the patients reported receiving both doses of the vaccine. And 19% were partially vaccinated.

Thus, the effectiveness of Pfizer and Moderna vaccines, at preventing hospitalizations, was 94% among fully vaccinated individuals. And 64% among those who had only received a single dose of either vaccine.

COVID-19 vaccines are highly effective and these real-world findings confirm the benefits seen in clinical trials, preventing hospitalizations among those most vulnerable. The results are promising for our communities and hospitals.

CDC Director, Rochelle P. Walensky, MD, MPH

Results Consistent with Clinical Trials

According to the study authors, the results are consistent with those observed in clinical trials of the vaccines. Previously, a real-world study from Israel also reported on the effectiveness of COVID vaccines at preventing symptomatic infection. However, the study has only looked at the Pfizer vaccine.

Moreover, CDC’s study revealed that the vaccines are not effective at reducing hospitalizations in partially vaccinated individuals. This includes people who received their first dose less than 2 weeks prior. This is because the body takes time to build up an immune response. Therefore, a person achieves a fully vaccinated status two weeks after their second dose.

This also highlights the continued risk for severe illness shortly after vaccination, before a protective immune response has been achieved and reinforces the need for vaccinated adults to continue physical distancing and prevention behaviours

study author

The results of the study further prove that vaccination efforts are a strong factor in reducing COVID-19 hospitalizations and reducing deaths.


Tenforde MW, Olson SM, Self WH, et al. Effectiveness of Pfizer-BioNTech and Moderna Vaccines Against COVID-19 Among Hospitalized Adults Aged ≥65 Years — United States, January–March 2021. MMWR Morb Mortal Wkly Rep. ePub: 28 April 2021. DOI:


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