People who were not fully vaccinated this spring and summer were ~10 times more likely to be hospitalized, and 11 times more likely to die of COVID-19, than those who were fully vaccinated, according to one of three major studies published mid-September by the CDC.
That study did not distinguish between which vaccine the vaccinated cohort received. But, a second study compared the different vaccines and found that the Moderna vax was somewhat more effective in preventing hospitalizations than the Pfizer and J&J vaccines. This assessment was based on the largest US study to date of the real-world effectiveness of all three vaccines, involving about 32,000 patients seen in hospitals, emergency departments and urgent-care clinics across nine states from June through early August. While the three vaccines were collectively 86 percent effective in preventing hospitalization, protection was higher among Moderna vaccine recipients (95 percent) than among those who got the Pfizer (80 percent) or J&J vaccines (60 percent). That finding echoes a smaller study by the Mayo Clinic Health System in August, which showed the Moderna vaccine to be more effective than the Pfizer vax at preventing infections from the Delta variant.
Vaccine effectiveness against infection dropped from 90 percent last Spring, when Delta had not yet gained significant traction, to less than 80 percent from mid-June to mid-July, when Delta began out-competing other viral variants. Importantly, effectiveness against hospitalization and death showed barely any decline during the entire period. Thus, all vaccines remain quite effective and useful in protecting against illness.
Why there is a difference in preventing infection between the Pfizer and Moderna mRNA vaccines was discussed earlier in these pages.