Sen. Elizabeth Warren (D-Mass.) and three other Democratic lawmakers are calling on the federal government to resume tracking all COVID-19 infections in fully vaccinated individuals, while also requesting that it provide racial and other demographic breakdowns for such cases.

The group of lawmakers penned a letter to Health and Human Services (HHS) Secretary Xavier Becerra and Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky on Tuesday asking that the department and agency “monitor, report, and address racial and other demographic disparities in COVID-19 breakthrough cases nationwide.”

Sen. Ed Markey (D-Mass.) and Reps. Ayanna Pressley (D-Mass.) and Barbara Lee (D-Calif.) also signed the letter.

The lawmakers said they are concerned that communities of color may be seeing a disproportionate number of COVID-19 breakthrough cases — as they note is happening with coronavirus infections and fatalities overall — but that they are “unable to identify and track racial disparities or other trends in these cases” without data collection.

The group also said they are urging the CDC to “collect and monitor racial and other demographic data related to COVID-19 breakthrough cases nationwide” because experts have said additional data on breakthrough cases could supply important information about the spread of new variants in the U.S., including the omicron strain.

The CDC announced in May that going forward it would only track COVID-19 breakthrough cases for infections that lead to hospitalization or death.

According to the lawmakers, only four states report data pertaining to race and ethnicity for COVID-19 breakthrough cases.

They said the limited pool of information that has been reported “suggest[s] the existence of racial and ethnic inequalities.” The letter cites data from King County, Wash., which the lawmakers say illustrates that hospitalization rates stemming from breakthrough cases are higher for Black, Indigenous and Pacific Islander individuals as compared to white residents.

The lawmakers are now urging Becerra and Walensky to “resume collecting data on COVID-19 breakthrough infections nationwide with breakdowns by race, ethnicity, and other demographic characteristics and to make this data publicly available as soon as possible.”

“Comprehensive data collection would allow experts to better understand patterns in breakthrough cases, identify COVID-19 variants earlier, and analyze the potential effect of compounding ‘racial and ethnic inequities in wealth, health, education, work, housing, and medical care’ on vaccine response,” they added.

The Hill reached out to the CDC and to HHS for comment.

The letter came two days after Warren announced that she tested positive for a COVID-19 breakthrough case. Sen. Cory Booker (D-N.J.) and Rep. Jason Crow (D-Colo.) also announced that they tested positive for breakthrough cases on Monday.

The CDC notes on its website that while COVID-19 breakthrough infections are expected, fully vaccinated individuals who test positive for the virus are less likely to develop serious illness compared to individuals who have not yet received the jab.

One day before the letter was sent, the CDC revealed that a majority of COVID-19 cases in the U.S. were tied to the new omicron variant, which was first identified in South Africa last month but has since spread globally.

The highly mutated strain accounted for 73.2 percent of COVID-19 cases in the U.S. as of Monday, according to the CDC.

Preliminary studies have found that the variant evades immunity gained from the vaccine at a higher rate than other strains of the virus, though they also say that a booster shot, in addition to an initial two-dose vaccine regimen, appears to provide strong protection against omicron infection.