A new study suggests immunocompromised Americans people who are fully vaccinated against COVID-19 are more likely to have breakthrough infections than people without weakened immune systems, but found full vaccination still adds more protection than being partially vaccinated.
Researchers from Johns Hopkins Bloomberg School of Public Health and the University of Washington found people with so-called immune dysfunction, including immunocompromised people like those with HIV or on immunosuppressant medications, had rates of breakthrough cases up to twice as high as those with normally-functioning immune systems.
"People with immune dysfunction conditions have a higher risk for COVID-19 breakthrough infection than those without such a condition, suggesting continued use of nonpharmaceutical interventions (mask-wearing, social distancing, avoid crowd gathering and travel, etc.) and alternative vaccine strategies (additional doses or immunogenicity testing) should be recommended even after full vaccination." Dr. Jing Sun, corresponding author of the study and an assistant scientist in the department of epidemiology at Johns Hopkins Bloomberg School of Public Health, told ABC News.
For the study, published in JAMA Internal Medicine Tuesday, the team looked at data from the National COVID Cohort Collaborative, which is a central database of COVID-19 data from academic medical centers across the country.
More than 664,000 people were included in the study between December 2020 and September 2021.
Patients were broken into two groups: with and without immune dysfunction. Those with compromised immune systems were broken down even further into patients with diagnoses such as HIV, multiple sclerosis and rheumatoid arthritis as well as people who had undergone organ transplants and bone marrow transplants.
A breakthrough infection was defined as someone who contracted COVID on or after the 14th day following vaccination.
Compared with only being partially vaccinated against COVID-19, being fully vaccinated was linked to a 28% reduced risk of breakthrough infection, regardless of immune system status.
However, those with weakened immune systems were at higher risk for breakthrough infection.
Throughout the study period, patients without immune dysfunction had a breakthrough infection rate of 7.1 per 1,000 person-months.
By comparison, those who had undergone bone marrow transplants had a breakthrough case rate of 8.6 per 1,000 person-months and multiple sclerosis patients had a rate of 8.9 per 1,000 person-months.
HIV patients had a rate of 9.1 per 1,000 person-months and rheumatoid arthritis patients had a rate of 9.3 per 1,000 person-months.
The highest breakthrough case rate was seen among organ transplant patients at 15.7 per 1,000 person-months -- twice as high as those who are not immunocompromised.
Researchers believe this is because transplant patients must be on immunosuppressants for the rest of their lives so their bodies don't reject their new organs. However, this also weakens their immune systems and makes them more susceptible to infection such as COVID-19.
The team said the findings provide further evidence that immunocompromised people may be at higher risk for breakthrough infection and that these Americans -- which make up an estimated 3% of the population -- should continue to wear masks even after being vaccinated and also should receive a third dose.
The findings have three caveats, with the first being that the study was conducted during the delta wave, before the omicron variant -- which appears to be more transmissible -- became dominant in the U.S.
Secondly, researchers only looked at the risk of breakthrough infection after a first and second dose of the vaccine and did not study the risk after a booster shot.
Finally, they only looked at certain immunocompromising conditions but not all, like cancers.
Booster shots were approved by the Food and Drug Administration and the Centers for Disease Control and Prevention for immunocompromised people in August and have been shown to boost antibody levels in immunocompromised people after being fully vaccinated.