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Vaccine advisers to the US Centers for Disease Control and Prevention voted unanimously on Friday to recommend an extra dose of Covid-19 vaccine for some immunocompromised people, and the CDC director signed off on the recommendation almost immediately.

The US Food and Drug Administration gave emergency use authorization Thursday night for a third dose in certain patients who are likely to have had a poor immune response to two doses of either Pfizer’s or Moderna’s vaccine. There’s not enough data to discuss the possibility for an extra dose of Johnson & Johnson’s one-shot Covid-19 vaccine, the FDA said.

That brought the question to the CDC and its Advisory Committee on Immunization Practices to decide whether to recommend that people actually get these extra doses.

“Yes, I agree …that the benefits are tremendous and the potential negative impacts are minimal and so I agree that we should recommend,” ACIP member Dr. Katherine Poehling, a professor of pediatrics and epidemiology at Wake Forest School of Medicine, said during the meeting.

CDC Dr. Rochelle Walensky quickly endorsed the vote, which means people can begin getting third doses right away.

“This official CDC recommendation — which follows FDA’s decision to amend the emergency use authorizations of the vaccines — is an important step in ensuring everyone, including those most vulnerable to COVID-19, can get as much protection as possible from COVID-19 vaccination,” Walensky said in a statement.

Covid-19 vaccine booster doses are not yet recommended for the general public.

ACIP said it should be left to the patients and doctors to decide who needs an extra dose and what the timing of that dose should be. People will be left on their own to attest to their need for the third dose – no prescription or doctor’s note will be needed.

The committee did not recommend any tests to see if people have had a sufficient response to the vaccine. No test is FDA-authorized for checking immune response after getting a Covid vaccine.

ACIP members discussed whether it would be safe to recommend giving a third dose of vaccine to immunocompromised children as young as 12 and decided to recommend including children 12 and over – who are included in Pfizer’s EUA – in their recommendation. Moderna’s vaccine is authorized for use in people 18 and older.

“This EUA is intended to be for people with moderate to severe immunosuppression and not persons with chronic conditions for which there might be mild associated immunosuppression,” the CDC’s Dr. Amanda Cohn told the meeting.

“The intent of our clinical considerations is to allow for some flexibility for providers to assess their patients’ immunosuppression and individuals will need to kind of attest to their immunosuppression to get vaccine,” Cohn added.

“But the intent of this is to limit this to individuals for which, are considered under the EUA to be moderate or severe and so, for example, would not include long-term care facility residents or persons with diabetes, persons with heart disease. Those types of chronic medical conditions are not the intent here.”

Some people have already jumped the gun – more than a million, the CDC found.

So far, “approximately, 140 million individuals completed a two-dose primary series of either Moderna or Pfizer/BioNTech Covid-19 vaccine,” Dr. Kathleen Dooling, of the CDC’s National Center for Immunization and Respiratory Diseases, said during the ACIP meeting.

“Approximately 1.14 million people – that’s less than 1% – received one or more additional Covid-19 vaccine doses.” And about 1% of the 12 million people who got a single dose of the J&J Janssen vaccine got a second dose of vaccine.

A recent study by Johns Hopkins researchers found that vaccinated immunocompromised people are 485 times more likely to end up in the hospital or die from Covid-19 compared to the general population that is vaccinated.

The CDC estimates about 7 million American adults – 2.7% of the adult population – are immunocompromised, either because of diseases they have or medications they take.

Disproportionate numbers of vaccine breakthroughs – when a fully vaccinated person gets infected anyway – are among immunocompromised people

“For breakthrough cases, there’s a larger proportion of immunocompromised ones in comparison to vaccinated cases,” the CDC’s Dr. Heather Scobie told ACIP.

Cohn told the meeting that vaccine effectiveness is about 59% to 72% in immunocompromised people, compared to 90% to 94% overall.

“Immunocompromised people are more likely to get severely ill from Covid-19. They are at higher risk for prolonged SARS-CoV-2 infection and shedding and viral evolution during the infection and treatment, particularly amongst hospitalized patients,” Cohn said.

“They are more likely to transmit SARS-CoV-2 to household contacts,” she added.

“Immunocompromised people are more likely to have breakthrough infection. In small studies of hospitalized breakthrough cases, 40 to 44% were deemed to be immunocompromised.”

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It has been known for months that Covid-19 vaccines might not work well for this group. The hope was that vaccination rates overall would be so high so that the “herd” would protect them. But it didn’t work out that way – about a third of eligible people in the US have not received even one dose of a Covid-19 vaccine.

While the vaccines protect well against severe disease, there are some breakthroughs. Out of 164 million people vaccinated, the CDC has counted 7,101 hospitalizations for Covid-19, with 1,507 deaths. That number is likely an undercount, the CDC says.