If You Got Pfizer, You May Not Have Antibodies Against Delta After This Long
A new study shows how much antibody response wanes against the dominant variant.
Throughout this past summer, as time marched further and further on from when some of the most vulnerable people in the U.S. got their initial COVID-19 vaccine doses, we saw an increasing number of infections among the vaccinated, AKA breakthrough cases. Though still rare, reports of breakthrough infections had many vaccinated people wondering if their protection against COVID-19 was dwindling, particularly as the more transmissible Delta variant became dominant. The good news is that not only is breakthrough COVID-19 rare, but just last week the Centers for Disease Control and Prevention (CDC) approved Pfizer boosters for a large swath of the population that's especially susceptible to severe COVID-19, whether because of age, underlying conditions, or increased exposure due to their living or working environments. Now, the latest research published on Pfizer's protection against the Delta variant may be just the push you need to get that booster.
A new study from researchers at Stanford University, Emory University, the University of Wisconsin, and the National Institutes of Health, which has yet to be peer reviewed, was posted on the preprint server bioRxiv on Sept. 30. The findings show how much antibodies wane from the Pfizer vaccine, especially against Delta, over time. To reach that conclusion, the researchers collected blood samples from 46 mostly young to middle-aged Pfizer recipients after they were vaccinated through the next seven months. They looked at both the neutralizing antibody responses and T cell responses in the participants to see how protected they were against certain variants of concern, including Delta, Beta (first detected in South Africa), and Mu (first detected in Colombia).
In 47 percent of the subjects, neutralizing antibodies that can block infection against the Delta variant were "undetectable" six months after the second dose. Though neutralizing antibodies are not the immune system's only defense against a virus, the researchers pointed out to Reuters, they "are critically important in protecting against SARS-CoV-2 infection." Another key factor is T cell response, and the data showed that while some levels "significantly downregulated" in the same timeframe, others "did not differ significantly." According to the authors, "These data demonstrate a substantial waning of antibody responses and T cell immunity to SARS-CoV-2 and its variants, at six months following the second immunization" with Pfizer.
"Our study shows vaccination with the Pfizer-BioNtech vaccine induces high levels of neutralizing antibodies against the original vaccine strain, but these levels drop by nearly 10-fold by seven months" after the initial dose, Bali Pulendran of Stanford University and Mehul Suthar of Emory University told Reuters via email. "These findings suggest that administering a booster dose at around six to seven months following the initial immunization will likely enhance protection against SARS-CoV-2 and its variants."
While these findings may seem startling, they're exactly what Pfizer has been preparing to combat with its booster. During a July appearance on CNBC's The Exchange, Pfizer CEO Albert Bourla discussed a company-funded study, which had not yet been peer-reviewed, that evaluated the Pfizer vaccine's efficacy among more than 44,000 recipients across the U.S. and in other countries over the course of six months. After four to six months, Bourla said Pfizer's efficacy was approximately 84 percent against symptomatic COVID, but was still 97 percent against severe disease. "The good news is that we are very, very confident that a third dose, a booster, will take up the immune response to levels that will be enough to protect against the Delta variant," he said.
In its emergency use approval ruling on Pfizer's booster, the U.S. Food and Drug Administration (FDA) shared a similar conclusion about the impetus for a third dose. "The recent emergence of the highly transmissible Delta variant of SARS-CoV-2 resulted in a new wave of COVID-19 cases in many parts of the world and has led to considerations for administration of booster doses to individuals who received primary series of vaccines in an effort to enhance immunity, and thus sustain protection from COVID-19," the agency said. As a result, they ultimately determined that a single Pfizer booster should be administered at least six months after completing the initial two-dose series, a regimen later confirmed by the CDC.