4:13 PM, Feb 27, 2020


Pfizer data suggest third dose of COVID-19 vaccine ‘strongly’ boosts protection against Delta variant

Posted at 3:55 PM, Jul 28, 2021
and last updated 2021-07-28 17:35:54-04

Pfizer released new data that suggests a third dose of its COVID-19 vaccine ‘strongly boosts’ protection against the highly contagious Delta variant. Our Chief Health Editor Dr. Partha Nandi tells us how much extra protection Pfizer’s third will provide.

Dr. Nandi: Let me break down for you what Pfizer did. They took a small number of participants, 23 of them, and split them into groups. After everyone was given a third dose of Pfizer’s vaccine, researchers then compared antibody levels against the Delta variant. They wanted to see if levels would be higher following a third shot compared to two shots. And here’s what was found.

A third dose provided five times the neutralizing antibody levels for the participants that were between the ages of 18 to 55. And for the participants aged 65 to 85, a third shot showed more than 11 times the antibody levels compared to a second dose against the Delta variant.

On top of that, Pfizer estimated that a third dose could potentially provide up to a hundred times the neutralizing antibodies in the study’s participants after receiving a third dose more than six months after vaccination. So while this preliminary data is based on a small number of participants, it’s still very encouraging.

Question: The CDC has said that Americans don’t need a booster shot. Since the CDC recently changed their guidance on masks because of the Delta variant, do you think they’ll be more open to booster shots?

Dr. Nandi: The Delta variant is definitely a different virus compared to when the pandemic first began. It spreads very easily. And yes the CDC did update its mask mandate, calling for vaccinated people to wear masks in areas where cases are spiking.

I would expect the CDC to change its stance on booster shots if breakthrough cases increase. Or if data shows COVID vaccines are losing effectiveness.

Now Pfizer is looking ahead at the future. And they’ve said that they’re in ongoing discussion with regulatory agencies concerning their third dose. And they hope to apply for Emergency Use Authorization this August.

If a third dose is given the green light, Pfizer’s plan is to focus on older adults and those who are immunocompromised. I think that’s a good strategic plan. Older folks and people with immune-compromising conditions tend to be at a greater risk than healthy people.

Thankfully, so far, breakthrough infections are still considered rare. Our vaccines continue to help protect those who are fully vaccinated against severe illness, hospitalization and death. So folks, please do not seek out a third dose. That is not needed right now.

Having said that, we definitely want to be prepared if anything changes.