Dr. Rachel Herlihy on Concerning COVID Breakthroughs

In September, the Colorado Department of Public Health and Environment began publishing data related to so-called COVID-19 breakthroughs — cases, hospitalizations and deaths among vaccinated people. Breakthroughs in each of these categories have been rising well beyond originally estimated levels, largely because of the dominance of the disease's more transmissible and dangerous Delta variant.

For the week of September 19, the most recent for which statistics are available, 100 percent of specimens collected and sequenced by the CDPHE were linked to the Delta variant. Not a single case of the original virus or any other variant was found.

Dr. Rachel Herlihy, Colorado's lead epidemiologist and the face of the state's scientific response to the disease, remains calm in regard to these findings. She stresses that immunizations do a great job of keeping people safe from the most severe potential outcomes of COVID-19, and says she is hopeful that improvements will be achieved if more Coloradans get their shots.

On September 30, Westword interviewed Herlihy about the breakthroughs via email, and she took advantage of the format to include her own links, connecting to a dozen sites that support and deepen her comments. Along the way, she reveals why the Delta variant has been so challenging, contrasts the efficacy of COVID-19 vaccines to those intended to fight the flu, discusses the prospect of new medications tweaked to combat specific strains, and tackles the issue of why even vaccinated people should continue to wear face coverings in public indoor places and engage in physical distancing.

Here's what she had to say:

Westword: The efficacy of the Pfizer and Moderna vaccines was originally estimated at being as high as 95 percent against the original COVID-19 strain. But the vaccines have proven to be less effective against the Delta variant. Can you explain in layman's terms why that's the case?

Dr. Rachel Herlihy: The vaccines are still highly effective against the Delta variant. No vaccine is 100 percent effective, and the effectiveness of these vaccines compared to some others is extraordinarily high. Because no vaccine is 100 percent effective, we expect to see some breakthrough cases with any vaccine, and the number of breakthrough cases will increase proportionately as more Coloradans are vaccinated.

Vaccine effectiveness can change over time as the characteristics of the virus change. The Delta variant has mutations in the spike protein on the surface of the virus that cause small changes to how the surface of the virus looks to the immune system. The Delta variant also makes more copies of itself inside an infected person. The combination of more virus that appears slightly different to the patient’s immune system can lead to a less effective immune response. CDPHE and CDC continue to monitor for viral mutations that may affect vaccine effectiveness. Most importantly, though, the available vaccines are still highly effective at preventing serious illness and hospitalization.

There are some groups of people who may need an additional dose or a booster dose to improve the protection provided by the vaccines either because their own immune response is limited or because their immunity may decrease over time.

Could you put the vaccines' level of effectiveness in context by comparing it to the effectiveness of other vaccines — such as the flu vaccine, for example?

The COVID-19 vaccines are highly effective at preventing severe illness and hospitalization. Every vaccine has its own vaccine effectiveness, and the effectiveness may change when considering different outcomes, like preventing infection versus preventing hospitalization.

CDC regularly posts influenza vaccine efficacy estimates for previous influenza seasons. For the 2019-2020 influenza season, overall influenza vaccine effectiveness was calculated to be about 39 percent, but variable by age, and more effective against preventing hospitalization and death. Though this may seem low, vaccination prevented an estimated 7.52 million illnesses, 3.69 million medical visits, 105,000 hospitalizations, and 6,300 deaths due to influenza throughout the US in the 2019-2020 influenza season.

No matter the type of vaccine or its specific vaccine effectiveness, the greater the number of people who get vaccinated, the greater the number of severe outcomes prevented and the greater the protection provided to those in our communities who are not able to get vaccinated or may not respond fully to vaccines. Influenza vaccines are currently available for this influenza season, and eligible individuals who have not yet been vaccinated should get vaccinated as soon as possible.

Some members of the public still seem confused by vaccine effectiveness, as if the immunizations haven't lived up to initial expectations. How would you explain to folks that they're actually performing remarkably well?

Our website shows the effectiveness of all three COVID-19 vaccines. We expect to see breakthrough cases with any vaccine, and these vaccines are proving to be highly effective, particularly when it comes to providing protection against severe illness and death. These vaccines are saving countless lives.

How does the percentage of breakthrough cases, hospitalizations and deaths in Colorado compare to those in other states?

Our website provides a breakdown of vaccine breakthrough cases by age group. Among breakthrough cases, individuals ages 30-39 are experiencing the highest percentage of breakthrough cases. This is likely because of their level and frequency of exposure. CDC provides limited data on breakthrough hospitalizations and deaths, but the general trends appear to be similar across the US.

As with any data, it is important to understand what metrics are being used, how they may be affected by other variables, and whether or not a direct comparison is appropriate. For vaccine breakthrough data, it is important to not directly compare the percent of all cases that are breakthrough cases alone across different populations. We know that this percent will increase with increasing rates of vaccination even as the total number of cases decreases. This is why our website shows case rates in the vaccinated versus the unvaccinated.

When it comes to breakthrough hospitalizations and deaths, they seem to generally be occurring in people over age seventy. Is that correct? If so, do many of these people have other conditions that make them more susceptible? Are booster shots expected to offer people in this age group greater protection? If so, how much?

Most breakthrough cases involving hospitalizations and death are among older individuals and those who have other significant medical conditions.

Our website provides a breakdown by age and shows the median age for each category. In each instance, the median age for the breakthrough cases is higher than for the unvaccinated category. This is especially true for breakthrough hospitalizations and deaths. National data presented by CDC shows a similar trend, with 86 percent of breakthrough deaths and 69 percent of non-fatal breakthrough hospitalizations occurring in individuals age 65 or greater. Additional information gathered by Colorado hospital systems also suggests that many breakthrough hospitalizations may have immunocompromising conditions that put them at additional risk for severe COVID-19 outcomes and reduced response to vaccination.

It is important that eligible individuals get vaccinated and that individuals who qualify for an additional dose due to immunocompromising conditions and those who qualify for a booster dose follow vaccine recommendations to ensure that they receive the highest level of protection against severe outcomes.

Each year, flu vaccines target particular strains. Are COVID-19 vaccine manufacturers working on a new vaccine that would more specifically target the Delta variant? If not, would you like to see that kind of targeting in the future?

Many vaccine developers (see Pfizer, Moderna, and AstraZeneca for examples) have released statements regarding ongoing work to develop variant-specific vaccinations. Importantly, all currently available vaccines continue to provide protection against severe illness and hospitalization with the Delta variant. The year-to-year changes in circulating influenza viruses are different from the kinds of changes we see in COVID-19, so it is still unclear if variant-specific vaccinations will be necessary in the future.

Quite a few people seem to believe the recommendation that even folks who've been vaccinated should continue to wear masks in public indoor places and keep maintaining physical distancing when possible means the vaccines aren't as good as they were supposed to be. How would you explain why that's an incorrect interpretation? Also, why are public-indoor-place masking and physical distancing still important practices even for vaccinated people — and how long would you estimate this will continue to be the case?

All currently available COVID-19 vaccines are highly effective at preventing severe illness and hospitalization. Getting vaccinated remains the most important thing we can do to protect ourselves and those around us. However, young Coloradans under age twelve are not yet eligible for vaccination, and around 24 percent of eligible Coloradans have not yet received their vaccine. While COVID-19 transmission rates are high, it is important to continue wearing a mask in public indoor places and maintain physical distancing with those outside your household to help reduce the spread of COVID-19.

As noted, the CDPHE breakthrough statistics show that certain demographics of vaccinated people are more likely to become infected — particularly people between the ages of thirty and fifty. Are there any current theories about why this might be the case in terms of age, as well as gender, since women appear to be more prone to breakthroughs, and race?

We are still learning about disease transmission, especially among the vaccinated. It is important to note that several factors likely play a role in the demographics of breakthrough infections. We suspect individuals between 30-39 (the age with the highest percent overrepresentation in breakthrough infection versus percent of those vaccinated) are more likely to have jobs that require direct interaction with the public, and this demographic might also be more likely to visit indoor spaces where there are larger crowds. The
Delta variant is more transmissible, so some of those settings pose increased risk. Similar explanations associated with job type and/or individual behaviors may help explain some of the other trends in breakthrough infections as well.

Does the CDPHE have a guess about what percentage of people in Colorado will need to be vaccinated in order for recommendations for indoor-public-place masking and physical distancing to no longer be necessary? Governor Polis continues to say that this is largely a pandemic of the unvaccinated: Is that true, and if so, why? And can you offer a bottom line about why vaccinations are still important even though breakthroughs continue to happen?

CDPHE and CDC recommend that vaccinated individuals wear masks in public indoor spaces in areas of high or substantial transmission. In areas with high or substantial transmission, there are high rates of actively infectious individuals in the community. It is not easy to tell if someone around you may be infectious, because many people have only mild symptoms or no symptoms at all.

With the highly infectious Delta variant putting most of Colorado in the highest transmission category, it is even more important for eligible individuals to get vaccinated and for everyone to practice the layered mitigation measures we know can reduce the spread of COVID-19.

Unvaccinated individuals continue to suffer the highest rates of severe COVID-19 illness, hospitalization and death. Those statistics, including the risk difference for unvaccinated versus vaccinated, are available on our website. Unvaccinated individuals are putting themselves, their families and their communities at additional risk. We need all Coloradans ages twelve and up to get vaccinated — it’s our ticket out of this pandemic.