By Published: July 26, 2021

Banner image: A mobile COVID-19 vaccination bus parks at the Williams Village residence complex at CU Boulder. (Credit: Casey A. Cass/CU Boulder)

This summer, cases of a mutated version of SARS-CoV-2—the virus that causes COVID-19—are increasing in Colorado, raising concerns among epidemiologists that a new stage in the pandemic could be underway. Called B.1.617.2 or the “delta” variant, this new type of coronavirus now accounts for nearly 90% of the COVID-19 cases in the state, according to recent data from the Colorado Department of Public Health and Environment. To date, Mesa County alone has recorded nearly 766 cases of COVID-19 caused by the delta variant, with Boulder County’s tally at 50.

The science surrounding the delta variant is evolving quickly. Read an Aug. 5 Q&A addressing the latest data on the pandemic.

Kristen Bjorkman, COVID scientific director for the BioFrontiers Institute at CU Boulder, and Matthew McQueen, professor of integrative physiology, have been following these cases closely. They spoke with CU Boulder Today about the new player in the pandemic and how Coloradans can stop its spread by getting vaccinated.

What is the Delta variant? 

BJORKMAN: “Delta” was first detected in India in October 2020 but has rapidly spread around the globe. It is a descendant of the original SARS-CoV-2, but it is called a variant because it has accumulated mutations (changes) in its genetic blueprint that give it slightly different properties. These include changes to the spike protein, which is the part of the virus responsible for attaching to our human cells. As a result, the delta variant is three to four times more infectious than the virus that emerged in 2019.

How is it different from other variants? 

BJORKMAN: Recent studies indicate that delta is up to 60% more transmissible than alpha (the variant first identified in the United Kingdom), which itself is more transmissible than the original form of the virus. Some data demonstrate that a person infected with delta becomes infectious to others more quickly and sheds about 1,000 times more virus. 

It is not yet clear whether delta causes worse disease or increased risk of death, but the sheer number of total infections means that many people have died from delta across the world.

Kristen BjorkmanMatthew McQueen headshot

Kristen Bjorkman and Matthew McQueen

Do COVID-19 vaccines work against this variant?

McQUEEN: Yes! The vaccines that are approved under Food and Drug Administration emergency use authorization and are widely available in the U.S. maintain high effectiveness against infection. Even when a person is infected by the delta variant, vaccines still offer excellent protection from severe disease. Anywhere from 97% to 99% of people hospitalized with COVID-19 in the U.S. are unvaccinated. 

If I’m vaccinated, should I still wear a mask or take other precautions when I’m around people who may not be vaccinated?

McQUEEN: As is true with any health-related issue, the risk of infection or disease is never zero. However, it is very unlikely that a vaccinated person who becomes infected will transmit the virus to someone else. This is why federal, state and county guidance, which we adhere to at CU Boulder, indicate that vaccinated people do not need to wear masks. It is, of course, important to finish your vaccine course and wait at least two weeks following your final dose (or single dose if you received the Johnson & Johnson vaccine) to ensure you’ve built up optimal immunity.

Can children who are not vaccinated spread COVID-19 to other kids or vaccinated adults?

McQUEEN: There is very low risk of children, particularly those under the age of 10, spreading COVID-19. In studies of both households and schools, the person who transmitted infection was almost always an unvaccinated adult. Child-to-adult and child-to-child transmission were the least common transmission patterns observed.

The most important thing you and others in your community can do for children is to get vaccinated.

Will I need to get a booster shot for my COVID-19 vaccine?

BJORKMAN: At this time, boosters are neither recommended by the Centers for Disease Control nor approved by the FDA. This is because the disease is well-controlled with the current vaccines and dosing strategies, no matter the variant. However, it is possible that this guidance will change in the future, so large studies are already underway to investigate if or when boosters should be given, who would need them and whether there should be tweaks made to the vaccine to make it more effective against variants such as delta.

Why isn’t campus requiring masks this fall?

McQUEEN: We have a vaccine mandate for students, faculty and staff at CU Boulder. Vaccines offer greater protection than masks, so the risk of a vaccinated person becoming seriously ill is very low. Moreover, the risk of a fully vaccinated person transmitting virus is also very low. Therefore, even a household with young children who cannot yet get vaccinated is at low risk if the adults are vaccinated.

What is your advice for people who are worried about the delta variant?

BJORKMAN: Get vaccinated! The best defense is an offense. There is a very clear relationship between the presence of delta and the vaccination rate of a community: the less vaccinated the community is, the more delta infections there are. This is true globally, nationally and across Colorado counties. 

Moreover, we need to be thinking ahead to the next variant. Delta will not be the last. Viruses have the advantage of speed: They can quickly hone their weapons while we play catch-up with our defenses. The COVID-19 deaths we see now are almost all preventable.