A BLOG ABOUT SCIENCE IN A WORLD OF UNTRUE FACTS

Finally some good news: CDC quarantine guidance updates

Kristen Panthagani, PhD

Exciting COVID update, that is actually good news!.

The CDC released some new recommendations about COVID, including what to do when a vaccinated person has a potential COVID exposure. Now, before I tell you the happy news, please know that the recommendation that vaccinated persons wear masks, social distance, etc. has NOT changed (yet). If you are fully vaccinated, you still gotta wear a mask and not throw house parties, etc.

CDC Quarantine Recommendations for Vaccinated People

Ok, now the good news. One recommendation has changed: quarantining after exposure to COVID. If the following criteria are met:

  • You have received all vaccine doses (2 for Moderna and Pfizer), AND
  • It’s been at least 2 weeks since the second dose, AND
  • It’s not been more than 3 months since the second dose, AND
  • You don’t have any COVID symptoms, AND
  • You’re not a resident (patient) of a healthcare facility….

YOU DON’T HAVE TO QUARANTINE!!!! WOOOO!!!!! Y’all, the end is in sight. This is exciting. It’s a step toward normalcy.

Does Vaccination Prevent Transmission?

So why did they make this decision? To answer that question, let’s review why transmission after vaccination has been a question mark. This has confused a lot of people.

The clinical trials evaluating the COVID vaccines studied symptomatic COVID infection, and found that that those who had been vaccinated were far less likely to get COVID than those who got placebo (i.e. the vaccine prevents symptomatic COVID infection). But the studies didn’t address asymptomatic infection and transmission… they didn’t test people every day to see if they were positive but asymptomatic, and they didn’t do contact tracing to see if those with asymptomatic infections spread it to other people. So the question of transmission wasn’t addressed in the study; we don’t have the data on it.

So let me say this very clearly: all the recommendations around transmission after vaccination have been based on the fact that WE DON’T HAVE THE DATA YET. We just don’t know, because we don’t have the data. Some people have misinterpreted this to say that the vaccines *don’t* prevent transmission. That is incorrect – we don’t know if they don’t prevent transmission, and we don’t know if they do. We just have to wait for the data to know one way or the other.

Now, is it likely that if the vaccines prevent, or at least reduce, transmission? Absolutely. I’d bet you money on it. But in science, we don’t like to guess, bet, or assume, we like to have data to back our decisions. So, because we didn’t study transmission after vaccination, we didn’t want to just assume vaccination prevent transmission and risk the consequences if we’re wrong. So why did the CDC change their quarantine recommendations?

First, let’s note again, so nobody gets confused, that they didn’t change their masking, social distancing, and travel recommendations for vaccinated persons. You can’t throw off your masks, or as some people like to call them, face diapers. While I am definitely pro-wear-a-mask-during-a-pandemic, I find the term face diaper hilarious… and accurate.. have you sneezed in your mask yet? It’s disgusting. And, also shows how well masks work.

So again, if you’re fully vaccinated, you DO have to keep wearing your face diaper, staying 6 feet away from people, and following all the public health recommendations. It’s only the recommendation around quarantine after COVID exposure that has changed.

So why did the CDC change this recommendation? Here’s what they said in their update:

“Although the risk of SARS-CoV-2 transmission from vaccinated persons to others is still uncertain, vaccination has been demonstrated to prevent symptomatic COVID-19; symptomatic and pre-symptomatic transmission is thought to have a greater role in transmission than purely asymptomatic transmission. Additionally, individual and societal benefits of avoiding unnecessary quarantine may outweigh the potential but unknown risk of transmission, and facilitate the direction of public health resources to persons at highest risk for transmitting SARS-CoV-2 to others.”

So basically, because the cost of making asymptomatic, exposed people quarantine is substantial (missed work, lost wages, etc.) and the risk of post-vaccination asymptomatic transmission is likely reasonably low, the cost-benefit analysis now favors no longer quarantining, if all the criteria above have been met.

Let’s do a quick quiz to make sure you understand those criteria. If you’ve been vaccinated, are exposed to someone with COVID, and start showing symptoms, do you get to skip quarantine? No. If you’ve been exposed and are asymptomatic, but haven’t been fully vaccinated? Still have to quarantine. And, I will say this a third time, this is not a free license to go breathe on people after vaccination. It’s just recognizing the significant burden that quarantine imposes, and that with vaccination, if the person is asymptomatic, the cost of quarantine now outweighs the benefit.

New Study on Viral Loads after Vaccination

Now, in related exciting news, there has been a new study (pre-print) that has come out about transmission after vaccination. First the caveats — this is a small study, and it’s not yet peer reviewed, and it has several limitations. So I’m going to ask you think like a scientist and not say ‘NOW WE HAVE ALLLLLL THE ANSWERS!!!’ but instead say ‘This is exciting preliminary data! But, we still need more data before we can make firm conclusions.’ Ok, ready? The study looked 28 days out after people received the first dose of the Pfizer mRNA vaccine, and found that SARS-CoV-2 viral loads were 4X lower after day 12. If you recall, Day 10ish is when antibodies start showing up after vaccination. So this coincides with 4-fold reduction in viral levels once antibodies start showing up after vaccination. And because the level of virus correlates with the risk of transmission, this suggests that vaccination may help reduce or prevent transmission (like we expected all along). Again, this data is not the end of the story, and we still need more data to know for sure how vaccination impacts transmission, but it is definitely good news.

That’s all folks. And remember, keep wearing a mask and social distancing, regardless of your vaccination status. Will it be like this forever? No. Is it still this way right now? Yes it is.

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