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Interaction 201: Updates for the COVID Vaccine Era

“Interaction 101,” coined by our daughter (and we have masks with that printed on -- any excuse for a little fun these days), was the introductory course: before vaccines, the syllabus was all about masks, air, and distance. We hope that by now, within your circle you have at least some vaccinated folks. Maybe a parent or grandparent, or health worker, or someone else whose turn arrived and was able to find available doses. A key question we’ve been getting is how vaccinated and unvaccinated friends and family members can safely interact. To answer, we need to review some of the risks we’ve covered before, and explore some new information to see what the advanced course, “Interaction 201,” can show us.


About a month ago we wrote that little would change immediately for vaccinated individuals, due to unknown levels of protection against asymptomatic infection: After you get your vaccine, you could still acquire and transmit COVID, without knowing it. We also thought that two weeks after the second vaccine dose, some limited changes could be possible, including expanding a bubble to include other fully vaccinated individuals. As more information emerges about vaccine effectiveness, our perspectives will change. Where we stand at the moment is based on four elements:


(1) The vaccines currently available in the U.S. now have real-world data showing effectiveness just as good as what we saw in the clinical trials, and fully vaccinated individuals are extraordinarily well protected against symptomatic illness, severe disease, and death;

(2) We don’t know how long this protection will last, but we expect vaccine-induced immunity should be at a minimum as durable as natural immunity, which could be at least eight months;

(3) Vaccine-induced immunity protects against the currently accelerating B.1.1.7 variant (and if you click on that link, the same study shows vaccine protection against other variants, while natural immunity may not work as well); and finally,

(4) While we still don’t know precisely how well the vaccine protects against asymptomatic infection, preliminary information is starting to emerge, ranging from 50% announced in a webinar, to at least 75% in early results from Israel, and more than 85% from a preprint from the U.S. As a potential additional layer of safety, initial findings indicate that among people who had received only one dose of vaccine and acquired COVID, viral load was lower; and we also know that lower viral load means lower risk of transmission.


So it’s possible that after vaccination you can carry and transmit COVID, or that you may fall ill. But the odds seem to be increasingly in your favor, as well as to the benefit of those around you. Critically important: this is promising but not proven. Here at Public Health Rising, we’re both vaccinated and we’re still taking precautions. Here are a few scenarios and how we would navigate them:

  • If you have been vaccinated and do not have anyone susceptible in your life (for example, you interact only with other immune individuals, and don’t have children or any high risk adults living with you), you can likely drop most precautions within that circle. You should continue all precautions outside of that circle.

  • If you have been vaccinated and previously avoided things like air travel, you should feel more comfortable taking that flight. You should still follow the recommended precautions, but can enjoy a greater sense of security.

  • If you have been vaccinated and interact with susceptible people, there would likely be little change in your precautions (note that health care professionals still continue their COVID protocols, despite a large proportion being vaccinated); but you could consider vaccination as a substitute for one of the three key risk-reducing factors shown in the CDC figure below. You should continue all precautions outside of that context.



These vaccines are slowly moving us towards community immunity. This remains an important concept, based on the idea that at a certain threshold of vaccine coverage (say, 70% of people or more), the community -- beyond just the vaccinated individuals -- is protected. This is because introduction of a disease, like COVID, soon hits a dead end in its attempts to spread. COVID needs susceptible people to act as viral hosts, and upon landing on vaccine-protected individuals, has less room to grow and/or mutate. Community immunity can also be important for vaccinated individuals, depending on vaccine effectiveness (an excellent 95% effective vaccine still leaves the door cracked open) and duration of protection, as we discussed above.


As it seems likely that the more contagious B.1.1.7 will become the dominant strain in coming weeks, there’s some concern that we will remain too far from the community immunity threshold to make a big difference in averting another surge of cases and deaths. While it is true that we’re not remotely close to community immunity across the total population, and some public health experts are advocating for a one-dose strategy to accelerate vaccination before B.1.1.7 takes over, it’s less clear where we stand with immunity among the most vulnerable groups. If we do have good protection for people age 65 and older, for example, we could see the equivalent of a bloodless coup: a spike in cases that has fewer hospitalizations and fewer deaths, due to protection conferred upon the most vulnerable groups. Unfortunately we don’t have ready access to the information that would help us determine where we stand. While it’s disappointing, we knew this to be the case: avoidable unknowns. Critical data for public health remains lacking. We are seeing information on vaccine coverage of the overall population, but the important piece here would be whether we have made enough progress on vaccinating those most likely to be hospitalized and die in the next surge. We can hope that’s the case, and of course we have many individuals who currently have natural immunity, following COVID infection -- they contribute to our estimates of community immunity as well.


We wish we knew more about where we stand with preparedness and protection against a B.1.1.7 surge. But as we approach the end of February 2021 we are in a pretty reasonable position, with at least a few angles that could lead to ongoing improvements and reasons to celebrate. Vaccines continue to roll out and we’ll find out this upcoming week if another good vaccine is going to be added to the list. Depending on how things unfold in the next month or two, we’re hopeful that by the end of summer 2021 we’ll have a significantly different, and brighter, picture in the U.S.

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