A new study of nearly 3.5 million Pfizer vaccine recipients finds the shots are 90% effective against severe COVID-19 illness for at least six months after full vaccination.
But the Pfizer-backed analysis of their vaccine, which was published Monday in the Lancet medical journal and conducted by researchers with Kaiser Permanente Southern California, showed that the shots’ effectiveness wanes after six months.
“The ability of the Pfizer-BioNTech vaccine to shield against infection fell by nearly half — from 88% at one month following the second dose, down to 47% — after six months,” the New York Post reported. “However, despite the shot’s declining defenses against viral transmission, it remained still an average of 90% effective against hospitalizations due to COVID-19, including the more aggressive Delta variant of 2021.”
In the study, researchers found that between December 2020 and August 2021, just 5.4% of people who took vaccine reported breakthrough infections. Of that group, just 6.6% needed to be hospitalized.
“Our study confirms that vaccines are a critical tool for controlling the pandemic and remain highly effective in preventing severe disease and hospitalization, including from the Delta and other variants of concern. Protection against infection does decline in the months following a second dose,” said the study’s lead author Dr. Sara Tartof in a statement, reported HealthDay.
“While this study provides evidence that immunity wanes for all age groups that received the vaccine, the CDC [Centers for Disease Control and Prevention] Advisory Committee on Immunization Practices has called for additional research to determine if booster shots should be made available to all age groups eligible for this vaccine,” she said.
The Food and Drug Administration (FDA) has authorized the use of boosters for the Pfizer vaccine for older adults and some with health issues, but scientists say more data is needed on whether boosters should be more widely administered.
The study found that vaccine effectiveness against the Delta variant of COVID-19 was 93% after the first month, but that declined to 53% after just four months. Against other coronavirus variants that have been circulating, efficacy declined to 67% from 97%.
“To us, that suggests Delta is not an escape variant that is completely evading vaccine protection,” Tartof said. “If it was, we would probably not have seen high protection after vaccination, because vaccination would not be working in that case. It would start low, and stay low.”
The decline in the effectiveness of the vaccine is “most likely due to waning and not caused by delta or other variants escaping vaccine protection,” Pfizer chief medical officer for vaccines Dr. Luis Jodar said. “Our variant-specific analysis clearly shows that the BNT162b2 vaccine is effective against all current variants of concern, including delta,” he said in a release published alongside the study.
Tartof also said the U.S. should make every effort to provide vaccines worldwide. “In line with the recent FDA and CDC recommendations, considerations for booster shots should take global COVID-19 vaccine supply into account as people in many countries around the world have not yet received a primary vaccination series,” Tartof added.