Though still relatively rare, breakthrough COVID infections have hit tens of thousands of people across the U.S. over the last few months, from celebrities like comedian Chris Rock and actor Hilary Duff to senators and professional baseball players. Research has determined that many different factors, including age and underlying medical conditions, can make someone more likely to catch the virus even after vaccination. But outside factors like the dominating Delta variant and the mere passage of time have seemingly played a part, too—at least for most of the vaccines.
A group of advisers from the CDC's Advisory Committee on Immunization Practices (ACIP) met on Sept. 22 to discuss the need for booster shots, showcasing vaccine effectiveness (VE) in the U.S. over time and through the rise of the Delta variant. The advisers used a set of data that analyzed this effectiveness against symptomatic infection during Delta from July 18 to Aug. 31, through nationwide community-based COVID testing of more than 519,000 participants between the ages of 20 and 64.
Ruth Link-Gelles, PhD, an epidemiologist and co-leader of the CDC's vaccine effectiveness team, said that the scientists have seen declines in VE against infection over time, except for one vaccine, as reported by CNN. According to Link-Gelles, Johnson&Johnson's effectiveness actually increases with time, even amid the dominance of the Delta variant.
According to the CDC's data, Johnson&Johnson's VE against symptomatic infection increases with time across all age groups up to 64 years old, as well as both before and during the new variant's spread. Through the Delta variant's rise, Johnson&Johnson's vaccine increased in protectiveness against symptomatic COVID from 49 percent two weeks after the shot to 56 percent nearly 150 days, or almost five months, after.
There was "no clear Delta effect on VE" for this vaccine, the researchers noted. But Moderna and Pfizer have not enjoyed the same fate. According to the data, Moderna's effectiveness in the face of Delta dropped from 95 percent two weeks after the second dose to 70 percent after around 250 days, or seven to eight months, while Pfizer's effectiveness dropped from 92 percent to 65 percent in the same time period.
The CDC's data echoes research recently released by Johnson&Johnson. The researchers for one study, which was pre-printed on medRxiv Sept. 21, analyzed more than 390,000 vaccinated individuals and compared them to more than 1.52 million unvaccinated persons. According to this study, Johnson&Johnson's one shot "demonstrated stable vaccine effectiveness" of 79 percent against COVID infections.
"There was no evidence of reduced effectiveness over the study duration, including when the Delta variant became dominant in the U.S.," the vaccine manufacturer said in a statement.
Other data released by Johnson&Johnson in July also showed that the vaccine produced a durable immune response that lasted through at least eight months. "Current data for the eight months studied so far show that the single-shot Johnson&Johnson COVID-19 vaccine generates a strong neutralizing antibody response that does not wane; rather, we observe an improvement over time. In addition, we observe a persistent and particularly robust, durable cellular immune response," Mathai Mammen, MD, the global head of research&development for Johnson&Johnson, said in a statement.