Becker's Hospital Review

84 CMO / CARE DELIVERY Fully vaccinated but COVID-19 positive? 5 notes on breakthrough case prevalence By Mackenzie Bean and Gabrielle Masson A tiny portion of people fully vacci- nated in the U.S. have developed breakthrough COVID-19 infections. While experts have confirmed these cases are rare, their exact incidence rate is still unclear, e Washington Post reported April 9. e CDC said April 15 it had found a small proportion of Americans — about 5,800 out of nearly 77 million — contracted COVID-19 aer being fully vaccinated against the infec- tion, according to CNN. Certain factors thwart fully understanding breakthrough case prevalence. Fully vacci- nated individuals oen forgo COVID-19 testing, and reports on breakthrough cases lag and may not reflect the most current events. e number of breakthrough cases identified by select states does not have Anthony Fauci, MD, President Joe Biden's chief medical ad- viser for the pandemic, overly concerned. "at number of individuals who were break- through infections is not at all incompatible with a 90-plus percent vaccine efficacy," Dr. Fauci said at an April 9 White House news briefing. "I don't think that there needs to be concern about any shi or change in the effi- cacy of the vaccine." Here's what we know: 1. Breakthrough infections are rare, but not unexpected. No COVID-19 vaccine re- ceiving emergency authorization from the FDA is 100 percent effective at preventing COVID-19 infection. Moderna's vaccine was 94.1 percent effective in a 30,000-person tri- al, and Pfizer's was 95 percent effective in a 38,000-person trial. e Johnson & Johnson vaccine was 100 percent effective at prevent- ing COVID-19 hospitalization and death, 85 percent effective at protecting against severe cases and 72 percent effective at preventing moderate illness in U.S. trials, according to the Post. Comparing the three vaccines' ef- ficacy rates is challenging because the trials were conducted at different times during the pandemic, and in different countries with different variants and transmission rates, experts told the Post. 2. State data underscores the rarity of such cases. For example, Michigan reported 246 infections and three deaths between January and March among 1.7 million people fully vaccinated, according to the Detroit Free Press. Washington state officials identified 102 breakthrough cases among more than 1 million people vaccinated between Feb- ruary and March 20. Of these cases, most had mild symptoms, eight people required hospitalization and two people, who both lived in long-term care facilities, died, the Post reported. At the end of March, Minnesota health of- ficials reported 89 COVID-19 infections in fully vaccinated residents. None of the 89 breakthrough infections account for any of the state's COVID-19 deaths. On March 24, Minnesota reported 1,454,834 residents had received at least one vaccine dose, with around 800,000 Minnesotans fully vaccinat- ed. Based on the 800,000 estimate, the 89 known cases would equal about one infec- tion per every 9,000 vaccinated. 3. Most people who experience break- through infections do not have severe cases, experts say. "e ones who are sick enough to warrant hospitalization, you can count them on one hand," Nicholas Gilpin, DO, medical director for infection prevention at Southfield, Mich.-based Beaumont Health, told the Post. His observation is based on Beaumont's efforts to track breakthrough in- fections among 161,000 vaccinated patients. Early research supports Dr. Gilpin's observa- tion. A study published March 23 in e New England Journal of Medicine found seven of 14,990 fully vaccinated employees across UC San Diego Health and the David Gef- fen School of Medicine at UCLA contracted COVID-19 two or more weeks aer their second dose. Most of the study participants who developed a COVID-19 infection aer being fully vaccinated had no symptoms or mild symptoms, indicating the vaccines were protecting against severe disease, according to Francesca Torriani, MD, lead study author and an infectious disease specialist at UC San Diego Health. e positivity rate for healthcare work- ers who contracted the virus two or more weeks aer vaccination was approximately .05 percent in the UC study, which was ac- tive for people vaccinated from December 16, 2020 through February 9, 2021. is rate is higher than those reported in authorized COVID-19 vaccine trials. Researchers said numerous factors could explain the elevated risk, including a regional surge at the time, regular access to testing for symptomatic and asymptomatic workers and higher overall exposure to the virus than participants in clinical trials. 4. e reason breakthrough infections oc- cur in rare instances is still unclear. Older people or those with compromised immune systems may generate weaker immune re- sponses to the vaccine, putting them at high- er risk for breakthrough cases, Dr. Fauci said during the April 9 White House briefing. "When someone is already elderly and may or may not have an underlying condition, that it is unfortunate, but not surprising that you might have a couple of deaths within that more than 200 people who broke through," Dr. Fauci said. Breakthrough cases reported to the CDC occurred among people of all ages eligi- ble for vaccination, though more than 40 percent occurred in people 60 or older, the agency said. Sixty-five percent of cases were female and 29 percent of the infections were asymptomatic. 5. Experts are still working to evaluate the effectiveness of the vaccines on COVID-19 variants. Early evidence suggests four of the CDC's five "variants of concern" show mini- mal to moderate reduction in neutralization by antibodies generated during previous in- fection or vaccination. Limitations to data are further compounded by the lack of information regarding variants' role in breakthrough infections. "People with breakthrough infections re- ally need to be studied," Eric Topol, MD, founder and director of La Jolla, Calif.-based Scripps Research Translational Institute, told e New Yorker. "e highest pri- ority is to sequence the virus of the breakthrough infections." However, vaccinated individuals are not likely to shed enough virus to sequence, meaning that breakthrough cases may pass under the radar, further complicating the effort to understand their incidence rate. n

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