Some conditions make a breakthrough infection more likely in a vaccinated person: more virus circulating in the community, lower vaccination rates and more highly transmissible variants.
If vaccinated people can get infected with the coronavirus, they can also spread it. Hence the CDC recommendation that vaccinated people remain masked in indoor public spaces to help stop viral transmission.
Using these criteria, the CDC guidance applied to 63% of U.S. counties on the day it was announced.
Who’s actually protected by masking recommendations?
The recommendation that fully vaccinated people continue wearing masks is primarily intended to protect the unvaccinated – which includes kids under age 12 who are not yet eligible for vaccines in the U.S. The CDC further recommends masking in public for vaccinated people with unvaccinated household members, regardless of local community transmission rates.
Unvaccinated people are at a substantially higher risk of getting infected with and transmitting SARS-CoV-2, and of developing complications from COVID-19.
How do new variants like delta change things?
Preliminary data suggests that the rise of variants like delta may increase the chance of breakthrough infections in people who received only their first vaccine dose. For instance, one study found that a single dose of the Pfizer vaccine had an effectiveness of just 34% against the delta variant, compared with 51% against the older alpha variant in terms of warding off symptomatic disease.
Other recent preliminary reports from highly vaccinated countries like Israel and Singapore are sobering, however. Before the delta variant became widespread, from January to April 2021, Israel reported that the Pfizer vaccine was 97% effective in preventing symptomatic disease. Since June 20, 2021, with the delta variant circulating more widely, the Pfizer vaccine has been only 41% effective in preventing symptomatic disease, according to preliminary data reported by Israel’s Ministry of Health in late July. An analysis using government data from Singapore demonstrated that 75% of recent COVID-19 infections were in people who were at least partially vaccinated – though most of them were not severely ill.
In all reports and studies, however, vaccines remain very good at preventing hospitalizations and severe disease due to the delta variant – arguably the outcomes we most care about.
With U.S. case counts and breakthrough infection numbers headed in what public health officials consider the wrong direction, it makes sense that the CDC would modify its masking recommendations to be more conservative.
What conditions in the US warrant masking up (again)?
The shifting recommendations don’t mean that the old ones were wrong, necessarily, only that conditions have changed. The bottom line? Masks do help cut down on coronavirus transmission, but it’s still vaccines that offer the best protection.
This is an updated version of an article originally published on July 22, 2021.