COVID breakthrough cases 3 times higher in immunocompromised people, Pfizer study says
Coronavirus infection after complete vaccination is possible but rare. Now, new research shows breakthrough cases are not only more common but also more severe in people with weakened immune systems.
The study, led by researchers from Pfizer who helped developed one of the three available COVID-19 vaccines, found breakthrough cases — infections that occur two or more weeks after complete vaccination — were three times higher in immunocompromised people, including those with cancer, HIV, kidney disease and organ transplants, compared to people without medical conditions.
Of the more than 1.1 million people included in the study, 978 (0.08%) contracted the coronavirus between December 2020 and July 2021 after receiving two doses of the Pfizer vaccine. All patients were ages 16 and older.
Immunocompromised people made up more than 38% (374 infections) of those breakthrough cases, even though they comprised just 18% of all studied infections.
People with weakened immune systems also accounted for about 60% of all COVID-related hospitalizations (74) and 100% of all deaths (2).
The findings, published Tuesday, Nov. 30 in the Journal of Medical Economics, underscore COVID-19 vaccines’ ability to protect healthy people from severe disease, and remind the public that immunocompromised people may not develop as robust antibody responses to the shots — or any at all.
The study was based on health care records submitted to U.S. insurance companies, including commercial, Medicare and Medicaid.
“Several countries are currently experiencing a resurgence of (coronavirus) infections despite the rollout of mass vaccination programmes. While COVID-19 mRNA vaccines help protect people from getting infected and severely ill, the risk of breakthrough infections in fully vaccinated people is not completely eliminated,” Manuela Di Fusco, lead study author from the Pfizer Health Economics and Outcomes Research team, said in a news release.
Researchers say their study emphasizes the benefits additional doses and boosters shots can play in people with weakened immune systems.
In August, the Centers for Disease Control and Prevention said immunocompromised people can get a third “additional” dose of either the Pfizer or Moderna coronavirus vaccines at least a month after their second dose of those same shots. Those who got the Johnson & Johnson vaccine were not eligible for an additional shot at the time.
Then in October, health officials said any adult who is moderately to severely immunocompromised and who received the Pfizer or Moderna vaccines can get a fourth “booster” shot of the Pfizer, Moderna or J&J vaccines at least six months after getting their third dose.
Adults with weakened immune systems who initially received a single dose of the J&J vaccine can get a single booster shot of the J&J, Pfizer or Moderna vaccine at least two months after getting their first dose. The CDC emphasizes people who got the J&J vaccine should not receive more than two COVID-19 vaccine doses in total.
Other studies have found similar results
People who had organ transplants included in the new study were the most likely to get infected after complete vaccination, as well as those with more than one medical condition and blood cancers. People taking “antimetabolite” drugs commonly used to treat leukemia and cancers of the breast, ovaries and gastrointestinal tract also faced high risks of breakthrough infection.
The findings align with other studies on immunocompromised people’s responses to COVID-19 vaccines.
A non-peer-reviewed study posted in June found that among a group of healthy people, 98% produced antibodies after vaccination, while only 37% of organ transplant patients, 55% of blood cancer patients, 82% of solid tumor cancer patients and 84% of those with autoimmune disorders developed the protective proteins.
Strikingly, about 95% of people with HIV developed antibodies after getting their shots.
People who received their organ transplant less than a year ago were less likely to respond to vaccination. Among transplant patients, those who received new lungs had the poorest immune response (22%), while people who got new livers developed the best (60%).
A separate study published in June also found that patients taking Rituximab, a medication used to treat blood cancers and autoimmune diseases, within six months of vaccination developed no antibodies. The University of Texas researchers also learned those on chemotherapy produced a muted response compared to the general population.
“How that relates to protection against COVID-19, we don’t know yet,” study co-author Dr. Dimpy Shah, a researcher with the UT Health San Antonio MD Anderson Cancer Center, said in a statement.
