There’s no one-to-one relationship between high viral load and infectivity, but we’re always making decisions based on imperfect data.Former CDC Dir. Tom Friedan on new data used to support a decision recommending masking for vaccinated people.
- In the past week, the CDC has discussed and published data showing the viral load for someone infected with the SARS-CoV-2 virus is the same whether a person is vaccinated or unvaccinated.
- The CDC has then raised the question about the potential for vaccinated people to spread COVID-19.
- Some doctors say the correlation between amount of virus and contagiousness is not automatic – that more research is needed to see whether the viral loads are equally contagious / easy to transmit.
- The CDC has also received criticism for not more aggressively tracking breakthrough cases of vaccinated individuals earlier this year. This makes it difficult to compare vaccinated breakthrough cases now as the delta variant challenges previous variants.
Why It Matters: New policies are being put into effect (e.g the new masking policy in the state of Louisiana) based on this new data despite these critiques.
The sentiments of Dr. Friedan were echoed by former FDA Commissioner Scott Gottleib in a recent interview:
“High levels of the virus in the nasopharynx of individuals who were vaccinated and became subsequently infected on par with the level of virus that you would see in someone who wasn’t vaccinated. But we know two things. First of all, nasopharyngeal swabs, the virus titers that you see in those nasopharyngeal swabs, while it’s suggestive of someone’s ability to spread the virus, it doesn’t prove that they’re able to spread the virus. So it’s not a perfect correlate with your ability to transmit the virus and how contagious you are. You really want to measure virus levels in the lower airways because that’s where aerosols are created. And we know that you spread this virus through aerosols. We also have other evidence that came out this week that people who are vaccinated, even if their viral titers are very high initially for the first 24 hours after they become infected, even if they- even if they’re asymptomatic and infected, we know their viral titers fall much more quickly than those who are unvaccinated. So maybe after a day or two days or three days, they’re much less likely to spread the virus than someone who remains unvaccinated. So initially, someone who’s vaccinated may- may have the same level to spread the virus, may be on par with someone who’s unvaccinated, but their ability to spread the virus probably diminishes more quickly. And therefore, out in the community, if you were measuring their ability to transmit the virus, you would probably see on the whole, they’re less likely to be contagious.”
by Jenna Lee,