Colorado’s Top Vaccine Experts Answer Common Questions About COVID-19 Variants, Vaccines for Kids, Vaccine Boosters and More

September 24, 2021


On September 15, Immunize Colorado hosted two of Colorado’s top immunization experts for a town-hall style panel discussion of the latest updates on the COVID-19 pandemic and vaccination. Panelists Dr. Sean O’Leary, Pediatric Infectious Diseases Specialist at Children’s Hospital Colorado, and Heather Roth, Immunization Branch Chief at the Colorado Department of Public Health and Environment (CDPHE), answered audience questions about COVID-19 variants, COVID-19 vaccines (including potential booster doses and availability for young children), and the status of routine vaccination in Colorado.

In this blog post, we share the panelists’ answers to some of the most common questions about the pandemic, COVID-19 vaccination, and routine vaccination in Colorado, as well as some resources that healthcare providers can use to continue encouraging vaccination in their patient populations.

(Please note that the landscape of the pandemic and vaccination continues to change rapidly; this information is current as of September 24, 2021.)

On Variants

How does the Delta variant compare to previous versions of the virus?

As far as infectiousness, the Alpha variant, which became predominant last winter, was 50% more transmissible than the original strain of COVID-19. The Delta variant is 50% more transmissible than the Alpha variant was. The R0, or average number of cases that will occur resulting from a single infected individual, is between 5 and 9 for the Delta variant, which is higher than what we saw with Alpha and the original strain. Delta is at least twice as transmissible and has made it more difficult to control the pandemic. It’s why we’re seeing a huge surge, particularly in places with under vaccination and places that have fewer protective measures in place.

As far as severity, there have been some studies that say Delta is more severe than previous strains, and some that say it’s less—essentially the science isn’t yet clear. There’s not a huge difference in severity for kids, either. But the focus shouldn’t be on severity, necessarily. Because Delta is far more transmissible, you could argue that it is more severe because it is infecting and hospitalizing a lot more people.

What percent of cases in Colorado can be attributed to Delta?

In Colorado, 99.77% of COVID-19 cases are the Delta variant. It is the predominant strain across the US.

How concerned are you about future variants?

Right now, we are focused on the Delta variant because it’s so highly transmissible. Could future variants become more transmissible? It’s hard to say at this point, but it’s certainly possible. Our biggest concern is getting vaccines in arms because we know vaccines are effective against Delta in protecting from severe illness that’s more likely to lead to hospitalization and death. In fact, there’s an inverse linear relationship when it comes to vaccination rates and hospitalization and death—communities with higher rates of vaccination have lower rates of hospitalization and death, and vice versa.

In essence, the vaccines are doing a great job at keeping people out of the hospital and keeping people alive. The vaccines have been effective against the Delta variant. Breakthrough cases are making headlines but are very uncommon compared to those who are being hospitalized who are by and large unvaccinated.

On Vaccine Boosters

What is the difference between an “additional dose” of COVID-19 vaccine and “booster dose”?

The difference is semantics. We’re still working to determine the best primary series for the vaccine; for immune-compromised folks, the CDC and FDA have determined that two doses of the mRNA vaccines don’t offer enough protection (or stimulate enough immune response) and therefore have authorized a third, additional dose for this population—meaning that the primary vaccine series for immune-compromised individuals is three doses.

A booster dose, however, is the term for an additional dose in people who mounted a sufficient immune response from the first two doses, but whose immunity may have waned over time.

What are the current recommendations for a booster dose for the public, and when might they be available?

The Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) met on September 17 and reviewed Pfizer’s application for booster doses for those 16 years and older. At this meeting, VRBPAC voted unanimously to approve a booster dose of Pfizer’s COVID-19 vaccine for those 65+ years and others 16+ at high risk for getting serious ill with COVID-19 or being exposed (such as healthcare workers), noting there is not yet enough data to support boosters for everyone 16+.

The CDC’s Advisory Council on Immunization Practices (ACIP) then met on September 23 to consider the FDA’s decision, and voted to recommend a booster dose of Pfizer’s vaccine for adults 65 and older, residents of long-term care facilities, and those over 50 at risk of getting severely ill from COVID-19 due to underlying health conditions. They also recommended a booster dose for people ages 18-49 with underlying conditions. The CDC adopted ACIP’s recommendation but went a step further to also recommend boosters for people 18-64 who live or work in settings that put them at high risk of getting COVID-19. (These recommendations are only for those who received an initial two-dose series of Pfizer vaccine; these individuals should receive a booster dose six months after their second dose.)

People might be confused by these new recommendations because of news earlier this summer that the White House wanted to make booster doses available to the public staring in September. However, the White House announcement was premature because the science was still unclear regarding the need for booster doses in healthy populations. We now have an official answer from the experts, which is that booster doses will only be needed, at least for now, for certain populations.

With the new recommendation, what is CDPHE’s plan for delivering/administering those doses?

CDPHE has looked at provider capacity to determine how many booster doses they could give per week, compared to booster doses planned based on different booster recommendations. CDPHE has well over enough capacity to vaccinate everyone eligible for a booster dose. They may employ some small vaccination clinics but are unlikely to reintroduce the mass vaccination clinic model.

What do we know about “mixing” vaccine brands for booster doses? In other words, if someone originally received Moderna, should they receive the same for booster dose?

There is not enough information on this, and it likely won’t be sufficiently studied to make a recommendation either way for some time. Right now, the recommendation for immune-compromised folks is to get the same product they got for their first two doses of mRNA vaccine; however, if the same vaccine is not available, they can receive the other brand. There is currently no recommendation for an additional dose of Johnson & Johnson vaccine, but one may come in the coming weeks.

On Covid-19 Vaccines For Kids Under 12

What is the expected timeline for COVID-19 vaccines to be available to those under 12 years old?

On September 20, Pfizer made an announcement that their clinical trial data showed a robust immune response from the vaccine in kids ages 5 – 11. Pfizer is expected to submit the data to the FDA shortly. It will take time for FDA to review the data, so the earliest we might see a formal authorization could be October. Pfizer will likely submit their data for 2 – 5-year-olds in November for FDA review. Moderna is several weeks behind Pfizer, so they may be submitting data for kids under 18 in the coming weeks.

Will the recommendations for the pediatric population be different?

Both Pfizer and Moderna are testing the vaccine at lower doses in the pediatric population, but their vaccine series’ will likely include the same number of doses and the same dose schedule as is approved currently.

Are the vaccines being tested against the Delta variant in pediatric populations? How does initial vaccine efficacy look for pediatric populations?

Right now, Delta is the main variant that’s circulating in the U.S., so the pediatric vaccines are automatically being tested against Delta. However, the trials in younger children are not looking specifically for vaccine efficacy, but rather they’re observing whether the vaccine elicits an immune response and comparing this to the upper age groups in which we know the vaccines are effective.

What should providers do to prepare for vaccinating younger populations with COVID-19 vaccine?

Providers should enroll as a COVID-19 vaccine provider if they are not already. CDPHE has recently announced the COVID-19 Primary Care Vaccination Program, which aims to increase engagement and enrollment of primary care providers in Colorado’s COVID-19 vaccination program by providing financial support to community-based organizations and health care service providers. Providers should also consider storage and handling requirements and prepare to have to store and administer additional doses of vaccine, including routine vaccines, flu vaccines and COVID-19 vaccines. Providers can focus on staff training, particularly in vaccine administration and motivational interviewing strategies to help parents make the decision to vaccinate their kids during office visits.

What are your thoughts/concerns about off-label use of COVID-19 vaccines in pediatric populations?

Safety is the top concern when vaccines is being studied, since they’re given to large populations of healthy people. In the US, we have a reliable process for reviewing and monitoring vaccine safety, and we need to stick to that process; it’s delivered us safe, effective vaccines for many decades. Right now, there is limited safety data on COVID-19 vaccines in younger age groups; until we see a recommendation from the FDA and CDC based on this data, we need to be very careful about giving the vaccines to kids who aren’t yet eligible under current recommendations, as doing so could be dangerous. Giving a young child a dose meant for an adult (or, in this case, meant for a kid over 12) could be problematic. Kids aren’t small adults; their immune systems are different, which is why the dose given to younger kids will likely be smaller.

What parents can do until vaccines are approved for their young children is make sure they’re vaccinated with other routine vaccines!

On Colorado’s School And Healthcare Worker Vaccination Requirements

Does CDPHE have any updates to share regarding the implementation of the new school entry immunization law that went into effect this school year? What proportion of exemptions are coming in through providers compared to the online education module?

CDPHE has a team supporting schools and child care centers in technical assistance for implementing the new law, especially the online module piece. So far, the department has seen 40,925 exemptions come through for 6,800 kids. Of these exemptions, 99% have been submitted through the online module, which means only 1% have been obtained through a healthcare provider. And 99% of the exemptions coming in are non-medical.

What is the new Board of Health requirement for healthcare worker COVID-19 vaccination?

The new requirement mirrors the influenza vaccine requirements that have been in place for years for healthcare workers, both contractors and direct staff. Healthcare workers will need to be fully vaccinated by October 31st. The requirement helps level the playing field across all facilities and will hopefully help to increase uptake at long-term care facilities, which have seen lower staff vaccination rates.

On Routine And Flu Vaccination

Can flu vaccine be co-administered with COVID-19 vaccine, and in the same arm?

Yes! Influenza and COVID-19 vaccines can be administered at the same time, in the same arm. The CDC has determined that the benefits of co-administration of the COVID-19 vaccine with other vaccines outweigh the potential minor risks. Co-administration is being tracked in the Vaccine Adverse Event Reporting System (VAERS) to continually monitor safety.

How can partners across the state support routine vaccination?

There’s not just one thing that can help increase routine vaccination—there are many evidence-based strategies. These include standing orders for vaccinations, reminder/recall to patients, patient communication and more. Providers should use CIIS to access their patients’ immunization data and see which patients need to be caught up. Engaging in as many of these strategies as possible will help improve routine vaccination.

What is encouraging is that we haven’t, anecdotally, seen a big shift in parents’ attitudes about childhood vaccinations.

On Provider Guidance For Covid-19 Vaccination

How should providers determine if someone is fully vaccinated, especially when administering booster doses?

The best practice is to use the Colorado Immunization Information System (CIIS) when determining someone’s vaccination history. All COVID-19 vaccine doses are required to be reported to CIIS.

Where would you recommend a provider seek guidance or additional input for specific patient situations where the recommendations for vaccination may be unclear for their circumstance?

Providers should carefully read the CDC recommendations on their website; the answers to some of these more specific questions are often included in the guidance. Providers can also consult the infectious disease specialists in their circles to see if they have recommendations.

CDPHE also has public health nurse consultants available. Providers may call 303-692-2700 to be triaged to a public health nurse consultant or send an email to The CDC also has an email address to which healthcare providers can submit immunization or vaccine-preventable disease related questions:

Related Resources

Immunize Colorado