U.S. Health Secretary Alex Azar and the director of the Centers for Disease Control and Prevention, Dr. Robert Redfield, have been subpoenaed by a House panel investigating the Trump administration’s response to the Covid pandemic.Rep. James Clyburn, chairman of the Select Subcommittee on the Coronavirus Crisis, said the panel issued the subpoenas Monday, ordering the two officials to produce documents that Clyburn said show political interference that hindered the nation’s response to the pandemic by Dec. 30.”The subpoenas were necessary because the Select Subcommittee’s investigation has revealed that efforts to interfere with scientific work at CDC were far more extensive and dangerous than previously known,” Clyburn said in a statement.Representatives for the Department of Health and Human Services did not immediately return CNBC’s request for comment.The subcommittee also released new emails that show political appointees at HHS attempting to alter the CDC’s prestigious Morbidity and Mortality Weekly Reports, or MMWRs. The emails also show appointees at HHS, including then-scientific advisor Paul Alexander and long-time Trump ally Michael Caputo, planning to publicly rebuke at least two published MMWRs.The subpoenas and new evidence come after the subcommittee released a slew of emails last week that offered a striking glimpse into the scope and degree to which political appointees attempted to shape policy work within HHS and the CDC. Still, the new steps taken Monday by the subcommittee represent a ratcheting up of the intensity of the probe, which began this summer.”While the Administration is focused on vaccination shots, the Subcommittee is focused on cheap shots to create headlines and mislead the American people,” an HHS spokesperson said in an email to CNBC, adding that HHS has handed “over 14,000 pages of documents over the last five weeks” to the panel.In one set of emails released by the subcommittee, political appointees discussed a draft of an MMWR rebuttal, which was never published, claiming that the MMWR, which was about the anti-malarial drug hydroxychloroquine, “presents factual information with an agenda” and could “prevent the news from giving the proper coverage of a true ‘miracle cure.'” Early in the pandemic, hydroxychloroquine was hailed by President Donald Trump and others as a highly effective treatment for Covid-19. The Food and Drug Administration authorized its emergency use to treat Covid, but later walked back the authorization, acknowledging there was evidence the drug could actually exacerbate some health conditions in Covid patients.Dr. Charlotte Kent, editor-in-chief of the CDC’s MMWRs, stated in an interview with the subcommittee that a public rebuttal to the CDC’s MMWR “could undermine confidence in CDC and in the quality of science that is in MMWR.” An HHS spokesperson said Kent’s “testimony shows there was no political interference in the MMWR process.”In another example of alleged political interference, HHS officials in July received a draft summary of an MMWR on a Covid outbreak at a Georgia summer camp. The report detailed how the virus spread rapidly at the camp, but Alexander said it was out of step with messaging from the White House.”I find it incredible this piece would be put out the way it is written at a time when CDC and its leader Dr. Redfield is trying to showcase the school re-open guidance and the push is to help schools re-open safely,” Alexander wrote in an email. “It just sends the wrong message as written and actually reads as if to send a message of NOT to re-open.”In response, CDC officials agreed to edit one line of the report to remove mention of schools. But Alexander drafted a rebuttal to that report, as well, sharing the un-published draft with Caputo on July 27.”Hi Michael, as requested, here is the piece to rebut that poor CDC MMWR,” he wrote. “I am not sure where it can be published but this has very re-assuring information and even for the White House.”Other emails released by the subcommittee show Caputo threatening CDC personnel for arranging interviews between CDC officials and the media.”If you disobey my directions, you will be held accountable,” Caputo wrote to a CDC official who appeared hesitant to reveal the names of the responsible communications personnel.One CDC official described Caputo’s behavior as “a pattern of hostile and threatening behavior directed at … communication staff at CDC,” according to the subcommittee.