Effectiveness Gap Between Moderna’s, Pfizer’s COVID-19 Vaccines Widens Over Time: Study

September 18, 2021 Updated: September 20, 2021

A new study seeking to shed light on real-world COVID-19 vaccine effectiveness shows a widening gap between Moderna’s and Pfizer’s vaccines four months after each vaccine’s second dose.

Among the 3,600-plus U.S. adults without immunocompromising conditions who were enrolled in the study, vaccine effectiveness against COVID-19 hospitalization within the first four months of being fully inoculated was higher for the Moderna vaccine (93 percent) than the Pfizer–BioNTech vaccine (88 percent) and the Johnson & Johnson vaccine (71 percent), according to the Centers for Disease Control and Prevention (CDC).

While the Moderna vaccine’s effectiveness dropped slightly to 92 percent after 120 days of full vaccination (with a median of 141 days), Pfizer’s declined significantly to 77 percent (with a median of 143 days), researchers found.

Because only a limited number of patients received the J&J shot more than 120 days before the onset of illness, its effectiveness wasn’t stratified by time in the study, which was conducted between March 11 and Aug. 15. Also, confidence intervals for estimating the J&J vaccine’s effectiveness were wide because of the relatively small number of patients inoculated with the product, according to researchers.

“Although these real-world data suggest some variation in levels of protection by vaccine, all FDA-approved or authorized COVID-19 vaccines provide substantial protection against COVID-19 hospitalization,” the CDC stated.

The study didn’t evaluate vaccine efficacy by variant, such as Delta, nor did it gauge effectiveness against COVID-19 that didn’t result in hospitalization. The analysis also didn’t consider effectiveness in children and immunocompromised adults.

COVID-19 is the disease caused by the CCP (Chinese Communist Party) virus, also known as SARS-CoV-2 or the novel coronavirus.

The study was published on Sept. 17, the same day that the U.S. Food and Drug Administration’s (FDA) vaccine advisory panel voted 16–3 to recommend booster shots of Pfizer’s COVID-19 vaccine for individuals aged 65 and older and those at high risk of occupational exposure. At the same time, the panel voted 18–0 against recommending booster shots for those aged 16 to 65.

Dr. James Hildreth, a voting member on the FDA expert panel, said that he “[has] a serious concern of myocarditis in young people.” The FDA had previously issued warnings that, while rare, Pfizer and Moderna vaccines, both of which are built on messenger RNA technology, could cause myocarditis or pericarditis among younger individuals.

Another FDA adviser, Dr. Melinda Wharton, echoed Hildreth’s concerns and said she would “not feel comfortable” with recommending boosters to younger people due to the risk of myocarditis. She noted during the panel that younger people are at very low risk of developing severe illness from COVID-19 or becoming severe breakthrough cases.

While U.S. health officials, some other countries, and vaccine makers have argued that boosters are needed for everyone, many scientists, including some inside the FDA and the CDC, have disagreed. Booster doses have been previously recommended by the CDC for immunocompromised individuals.

Jack Phillips contributed to this report.

Tom Ozimek
Tom Ozimek
Tom Ozimek has a broad background in journalism, deposit insurance, marketing and communications, and adult education. The best writing advice he's ever heard is from Roy Peter Clark: 'Hit your target' and 'leave the best for last.'