(NEXSTAR) — CNN’s John King revealed on Tuesday he has multiple sclerosis and is immunocompromised during a conversation about how vaccines help protect vulnerable people like himself.

“I’m going to share a secret I’ve never shared before … I have multiple sclerosis,” King said Tuesday. “So I’m grateful you’re all vaccinated.”

King continued: “I worry about bringing it home to my 10-year-old son who can’t get a vaccine,” he said. “I don’t like the government telling me what to do. I don’t like my boss telling me what to do. In this case, it’s important.”

The conversation centered around the death of Colin Powell, who was fully vaccinated and died Monday of COVID-19 complications. Powell was also immunocompromised.

The death highlights the continued risk to many Americans until more of the population is immunized.

Powell, the first Black person to be national security adviser, chairman of the Joint Chiefs and secretary of state, was 84 and had been treated over the past few years for multiple myeloma, a blood cancer that impairs the body’s ability to fight infections — and to respond well to vaccines.

US is expected to authorize mix-and-match COVID-19 booster shots

Federal regulators are expected to authorize the mixing and matching of COVID-19 booster doses this week in an effort to provide flexibility as the campaign for extra shots expands.

The upcoming announcement by the Food and Drug Administration is likely to come along with authorization for boosters of the Moderna and Johnson & Johnson shots and follows the OK for a third dose of the Pfizer vaccine for many Americans last month.

The move was previewed Tuesday by a U.S. health official familiar with the matter who was not authorized to speak publicly ahead of the announcement.

The FDA was expected to say that using the same brand for a booster was still preferable, especially for the mRNA vaccines from Pfizer and Moderna that have proved most effective against the coronavirus. The agency was still finalizing guidance for the single-shot J&J vaccine.

Preliminary results from a government study of different booster combinations found an extra dose of any type revs up levels of virus-fighting antibodies regardless of the brand people first received. But recipients of the single-dose J&J vaccination had the most dramatic response — a 76-fold and 35-fold jump in antibody levels, respectively, shortly after either a Moderna or Pfizer booster, compared to a four-fold rise after a second J&J shot.

One confusing decision is what Moderna dose to recommend in combination with other brands. Moderna has applied for its booster to be half the original dose, saying that’s plenty for people who already received two full-strength shots. But the mix-and-match study used full-strength extra doses, and there’s no way to know if a half-dose Moderna booster would trigger as strong a reaction in J&J recipients.

Allowing mixing and matching could make the task of getting a booster simpler for Americans and allow people who may have had adverse reactions to the initial dose to try a different shot.

Last week, the U.S. said it would recognize combinations of vaccines administered overseas for the purposes of entering the country. The practice was common in Canada and some European countries in the early months of the vaccination campaign.

The Associated Press contributed to this story.