Thread by @DrTomFrieden

I’ve heard concern over the past few days about the impact of Delta, and questions about new guidance from the CDC. The bottom line is the virus has adapted and we must adapt too. Delta is different, but our vaccines are still doing their job. 1/thread

Earlier this week, CDC issued new guidance that everyone—vaccinated and unvaccinated​​—should wear masks indoors in areas with high rates of Covid. And last night, information was published referencing new evidence and new challenges posed by Delta. wapo.st/3lfovuy 2/

Delta is at least 2x as transmissible as the original virus, and appears to be among the more infectious viruses, estimated to spread about as readily as chickenpox. But Delta can be controlled, just as we’ve controlled chickenpox​​—through vaccination & other measures. 3/

Before Delta, it seemed that people with breakthrough infections were unlikely to transmit the virus. Unfortunately, Delta has changed the calculation. 4/

We don’t know if Delta causes more severe infections than other variants. Some studies have suggested this, but comparing severity among variants is hard. ALL Covid strains can cause severe disease in the unvaccinated, especially those over 65 and with underlying conditions. 5/

No vaccine is perfect. Breakthrough infections are expected, as we expect them with every vaccine. It’s worth remembering that vaccines are stunningly effective at preventing infection and even better at preventing serious illness if an infection does occur. 6/

Today, CDC released a report of an outbreak in Provincetown, MA, where nearly 500 Covid cases were detected—most among fully vaccinated people. 7/

This study also showed, surprisingly, that people with breakthrough Delta infections had high viral loads (i.e. lots of virus in their secretions, suggesting that they could be infectious). bit.ly/3zRMK5L 8/

Evidence from this report can’t be used to draw conclusions about vaccine effectiveness or about the risk of transmission from breakthrough infections. That’s because we don’t know how many people in total were exposed and because onward transmission was not assessed. 9/

But the report DOES suggest that masks and other measures may be necessary to prevent the spread of Delta, especially in crowded indoor settings and mass gatherings. 10/

Outbreaks of Covid among fully vaccinated people sound alarming, but we have to look at the numbers overall. How many in the population are vaccinated and unvaccinated? 170 million people in the US are vaccinated, we can expect tens of thousands of breakthrough infections. 11/

Big picture: Your chances of getting a breakthrough infection after vaccination are low, and, if you do, your risk of serious illness or death is extremely low. However, it does appear that Delta is more likely to cause breakthrough infections than other variants. 12/

We’re still learning about whether people with breakthrough infections after vaccination can develop long Covid, and, if so, whether they are at lower risk. It appears that they may, although we lack data on Delta. bit.ly/3C15Bxm 13/

Given high rates of transmission, many people (including young kids) still not vaccinated, and open questions on the risk of breakthrough transmission and long Covid, it's better to be safe than sorry. CDC’s current masking guidance is appropriate and sensible. 14/

For most of us who are vaccinated, that means we can continue nearly all of the activities we resumed, just with masks again. 15/

Vaccinated people who are immunocompromised or who live with unvaccinated people may choose to go further, using N95 masks, increasing ventilation, maintaining physical distance, and avoiding crowds. 16/

Remember, respiratory diseases such as Covid spread when infectious particles enter the nose and mouth. Masks reduce the amount of particles an infectious person emits and the amount of particles someone else could be exposed to. 17/

https://twitter.com/DrTomFrieden/status/1277638088555102208?s=20

Vaccination is our most powerful tool against the virus, and masks are an extra layer of protection. Nearly every hospitalization and death from Covid is now preventable. Delta is serious, but protection by vaccines is holding. 18/

Going forward, we may need to optimize the vaccine series for immunocompromised people to increase their protection. But now is NOT the time to be talking about boosters or a “third shot” for everyone. 19/

Our vaccines are working exceptionally well and we are monitoring if, when and for whom that may change. That should be determined by breakthrough infections, particularly that cause serious illness. 20/

Delta emerged because of uncontrolled spread, and I worry that even more dangerous variants—including vaccine-resistant ones—could emerge if uncontrolled spread continues. Low vaccination rates put us all at greater risk. We must expand vaccination in the US and globally. 21/

Bottom line: Getting vaccinated is the most important thing we can do to protect ourselves from Covid. Until more are vaccinated and we learn more about the risks of Delta breakthroughs, wherever Covid is spreading widely, EVERYONE should mask up indoors to reduce spread. 22/end