CDC Director Says People Should Make 'Judgement Call' on 2nd Booster Timing

People should use their own judgement to decide when is best for them to get a second COVID booster vaccine, Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention (CDC), has said.

Last week, the CDC recommended second booster doses—a fourth shot for many people—for certain immunocompromised individuals and people over the age of 50 as long as they had received their initial booster dose at least four months prior.

It followed the authorization for a second booster dose of either the Pfizer or Moderna mRNA COVID vaccines by the Food and Drug Administration (FDA) on March 29, on the basis that "emerging evidence suggests that a second booster dose of an mRNA COVID-19 vaccine improves protection against severe COVID-19 and is not associated with new safety concerns."

Speaking to NBC News, Walensky provided some further guidance on when those eligible might choose to have the second booster dose.

She said that for people who have already caught the Omicron COVID variant in the past two or three months, the disease "really did boost your immune system quite well" and that they could wait another two to four months before their second booster.

Rochelle Walensky
CDC director Rochelle Walensky speaks at a Senate hearing in Washington D.C. in May, 2021. The CDC recently recommended additional COVID booster vaccines for certain individuals. Greg Nash/Pool/Getty

There is also the issue of the vaccine's protection decreasing over time. Last week, Dr. Richard Besser, former acting director of the CDC, told NBC that people should "think thoughtfully" about when they want to get their fourth dose.

"If you're in an area where [COVID] is really, really low and you get the booster now and two, three months from now the rate goes up higher, I don't know [if] you're going to have the same protection than if you wait a couple months. So that's why I would say pay attention to what's going on locally. This is one of those situations where talking to your doctor really matters."

On this, Walensky said it is a "personal judgement call" for individuals.

Her comments comes after data from Israel suggested that the protection against confirmed infection offered by a fourth dose of the Pfizer vaccine "appeared short lived"—though it should be noted that protection against severe illness did not fall during the study period.

The researchers used data on 1.25 million people from the Israeli Ministry of Health database who were 60 years of age or older and eligible for a fourth dose between January 10 and March 2, 2022.

The people involved in the study were split into three groups. COVID infection and severe illness was estimated starting eight days after receipt of a fourth dose (the fourth dose group) compared to a three-dose group, and a group who had received a fourth dose three to seven days earlier (internal control group).

The researchers found that the rate of severe COVID in the fourth week after receipt of the fourth dose was lower than that in the three-dose group by a factor of 3.5 and that protection against severe illness did not wane in the six weeks after the fourth dose.

Confirmed infection was also lower in the four-dose group by a factor of 2 after four weeks, but "this protection waned in later weeks," the researchers wrote.

The study was published in The New England Journal of Medicine on Tuesday.