Thread by @DrTomFrieden

CDC recommended today that some people with weakened immune systems get a third dose of mRNA vaccine as part of their primary series to achieve better protection from Covid. This recommendation makes sense. 1/thread

About 2.7% of US adults—roughly 7 million people—are immunocompromised, which means they have a condition that may interfere with how their body responds to infections as well as to vaccines. Here are CDC’s new recommendations: bit.ly/3CPngZ0 2/

Evidence shows that people with these conditions are at higher risk of severe illness and death from Covid, can shed virus longer and transmit it more to household contacts if they get infected, and are less protected by vaccines. 3/

There’s also a possibility that the virus can mutate more in people with weakened immune systems because their bodies take longer to clear the virus, giving the virus more time to evolve. nyti.ms/3g1p1J3 4/

Through monitoring, we've learned the two-dose mRNA series isn’t working as well for immunocompromised people as for other people. They're more likely to have a breakthrough infection, and, according to CDC, make up 40-44% of all hospitalized breakthrough cases in the US. 5/

Fortunately, there’s evidence that three doses in immunocompromised people are safe and may improve protection. Among immunocompromised people who didn’t have an antibody response to the first two doses, a significant proportion DID generate antibodies after a third dose. 6/

The presentations CDC staff made to ACIP are superb. A model of what public health should be: Clear, evidence-based, thoughtful, expert, and transparent. Thousands of CDC staff work hard every day to protect us. The slides are here. bit.ly/3ka2k6T 7/

For all of these reasons, CDC now recommends an additional dose of Pfizer or Moderna for moderately and severely immunocompromised people at least 28 days after their second one—preferably the same vaccine they’ve already received. cnn.it/3yS3xWA 8/

Groups recommended to receive a third dose:

-Treatment for solid tumor and blood cancer
-Solid-organ or stem cell transplant
-Severe primary immunodeficiency
-Advanced or untreated HIV infection
-Treatment with immunosuppressive drugs such as high-dose steroids

9/

The last group is large, and includes people not only being treated with high-dose steroids, but also alkylating agents, antimetabolites, tumor-necrosis blockers, and other biologic agents. 10/

There’s evidence from flu vaccination that some people on these treatments benefit from stopping treatment for a week or two after vaccination, if that’s clinically safe. If you’re being treated with a drug that may weaken your immune system, consult your clinician! 11/

Layers of protection still matter after the third dose. Until guidance changes, immunocompromised people—including those who receive a third dose—should continue to mask indoors (my 2 cents—with an N95 mask), distance, and take other precautions when case rates are high. 12/

Close contacts of immunocompromised people should get vaccinated to help protect the immunocompromised. 13/

What do these recommendations mean for immunocompromised people who got the one-dose J&J vaccine? Unfortunately, we don’t have good data for J&J, but these recipients certainly need guidance. CDC and FDA say they're working on it. 14/

In my opinion, immunocompromised J&J recipients may consider getting at least one dose of an mRNA vaccine, though CDC has not yet recommended this. 15/

Note that none of this is about the need for booster shots because of waning immunity. Waning immunity MAY occur. And it MAY be the case that we will need tweaked vaccines because of variants. We don’t know yet. 16/

The data on waning immunity isn’t there, although some preliminary results from Israel and elsewhere hint that either Delta or waning immunity may account for some breakthrough infections. (It’s hard to distinguish Delta from waning immunity as a cause of more breakthroughs.) 17/

It will be important to continue monitoring vaccine safety and effectiveness going forward. Bottom line: Our vaccines are doing their job—and now immunocompromised people can be more confident they’re getting more protection. 18/end