Pfizer Vaccine Infection Efficacy Wanes, But Protection Against Hospitalization Stays Strong
Although efficacy of the Pfizer vaccine against nonDelta COVID-19 infection dropped from 97 percent to 67 percent after five months, its protection against COVID-19 hospital admission — including admissions with Delta variant illness — remained high, according to a large database study published this week in The Lancet.
The review of 3.4 million patient records also found that efficacy against Delta variant infection started out at 93 percent and waned to 53 percent after four months, reported Sara Y. Tartof and colleagues. But the vaccine continued to provide 93 percent protection against Delta-associated hospitalization.
The findings suggest that Delta isn’t driving the vaccine efficacy changes. “Reductions in vaccine effectiveness over time are likely to be primarily due to waning vaccine effectiveness rather than the Delta variant escaping vaccine protection,” wrote Tartof, an infectious disease epidemiologist for Kaiser, and her team.
The study followed patients from December to August. Delta infections rose from 0.6 percent in April to 86.5 percent by July. During the study period, 5.4 percent of subjects experienced a breakthrough infection; of these, 6.6 percent required hospital treatment. Hospitalized patients tended to be younger (42 vs. 45 years), Hispanic and obese. Males and those with medical comorbidities were also more likely to be hospitalized.
The findings mirror recent Israeli data, showing reductions in the Pfizer vaccine’s effectiveness against infections by five months. And while the vaccine’s protection against hospitalization in Israel has remained generally strong, there are a few troubling numbers popping up, the investigators said.
“The most recent report … suggests that some reduction in effectiveness against hospital admissions has been observed among [people aged 65 and older], roughly six months after receiving the second dose. … Thus, long-term effectiveness data against severe outcomes should be continuously monitored in our study population and globally.”
The Moderna vaccine also confers waning protection, studies are finding. But the newest data, including unpublished data from a large Israeli health maintenance organization, continue to show that boosters can overcome this problem, Dr. Tartof said.
“[The data] suggest that a third booster dose is highly effective in a setting in which the Delta variant accounts for nearly all cases. These findings suggest that boosting with the current [Pfizer] vaccine rather than a Delta-specific vaccine might be effective.”
The study was funded by Pfizer.
Read the full study report here: https://bit.ly/3lbea2b. — Michele G. Sullivan