In-Depth: Debunking the claim that vaccines don't prevent infection

COVID-19 vaccine
Posted at 6:53 PM, Nov 24, 2021
and last updated 2021-11-24 22:13:19-05

SAN DIEGO (KGTV) — As families gather for Thanksgiving, you might hear bits of vaccine misinformation, such as the misleading claim that vaccines do not prevent COVID infections or transmission.

Governor Ron DeSantis (R-Florida) put it this way during a bill signing event this month: “The data is very clear at this point. COVID vaxes are not preventing infection.”

That claim stems, in part, from an October study in the journal Lancet.

The authors looked at COVID transmission in households. Among several other findings, they showed that when a vaccinated person came home with a breakthrough infection, they transmitted the virus to the same number of household members as an unvaccinated person with an infection.

One reviewer wrote the study “highlights that the vaccine effect on reducing transmission is minimal.”

Case closed?

Doctors say hold on. The Lancet study presents a very specific frame of reference: in a situation where a vaccinated person already has a breakthrough infection, then returns home, how many people do they infect?

“It’s a totally different thing to say that the vaccines do not prevent transmission. It’s a complete distortion of the facts,” said Dr. Christian Ramers of Family Health Centers of San Diego. “What’s happening here is people cherry-picking little tiny pieces of information without going deeper.”

It’s been clear from the beginning when Pfizer and Moderna announced their COVID vaccines were 95% effective against symptomatic disease, that these shots would not prevent all infections. But infectious disease experts say there’s plenty of evidence they do prevent many infections.

“The reality is if you are vaccinated, you’re much less likely to get COVID and then to spread COVID,” said UCLA epidemiologist Dr. Anne Rimoin.

Even after months of waning immunity, studies repeatedly show vaccines prevent more than 50 percent of infections, with or without symptoms. The vaccines are more effective against symptomatic disease and extraordinarily effective against hospitalization-level disease, with estimates remaining close to 90 percent.

If a vaccinated person doesn’t get an infection in the first place, they can’t transmit the virus to anyone.

But there’s also emerging evidence, not yet peer-reviewed, that adds support to the idea that vaccinated people with a breakthrough are less infectious than their unvaccinated counterparts.

It has to do with studies on “viral load,” a measurement of the viral particles in a person’s blood.

Vaccine critics argue these tests show vaccinated people with a breakthrough are just as infectious as the unvaccinated because their viral loads peak at roughly the same level.

But that’s not necessarily true, Dr. Ramers said, because of an important limitation with the way a viral load test works. It can sense the virus’ code, or RNA, “but it doesn’t give any context of what else is going on around that RNA.”

That means a test in a vaccinated person might appear similar on the surface, even though many of the viral particles in their bloodstream have already been neutralized by antibodies.

A study led by researchers at the University of Illinois found vaccinated people with a breakthrough emit fewer viral particles and weaker ones, and they shed virus for a shorter amount of time.

A study from the Netherlands on household contacts backs up the idea that vaccination reduces transmission, even in the era of delta. In that study, vaccinated people with breakthrough infections transmitted the virus to 63 percent fewer unvaccinated household contacts.

Even the study in the Lancet found fewer vaccinated household contacts got infected than unvaccinated ones.

“Vaccinated people were less likely to be infected in the first place, and the people making this talking point just forget to mention that I guess,” said Ramers.