Pitkin County is seeing a low incidence rate, which points to our high vaccination rate among our residents. However, neighboring counties, states, and countries – especially those who have a low vaccination rate – are facing a much more dire situation due to the spread of the Delta variant. With an anticipated busy summer headed our way, we must be sure to continue to stay on the right path by getting fully vaccinated, as those who are not vaccinated or not fully vaccinated run a higher risk of infection of the Delta variant. Learn more about the Delta variant below.
Overview of the Delta Variant
Like all viruses, SARS-CoV-2, the virus that causes the infection known as COVID-19, mutates. This means the genetic structure of the virus changes. Some of these changes do not help the virus survive or increase its infectivity. The changes that do help the virus survive or become more infectious tend to hold. During the pandemic, we’ve referred to viruses with mutations that benefit the virus and make it more infectious as variants.
Specifically, the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) classify all variants into three categories: variants of interest (VOI), variants of concern (VOC), or variants of high consequence (VOHC). As of June 25, 2021, there are no variants classified as variants of high consequence, although several are classified as VOCs. VOCs are defined as variants that are more transmissible, cause higher rates of hospitalizations and death, are more likely to evade human antibodies, and for which certain treatments may not be effective.
Read an in depth report about the Delta variant from Josh Vance, Pitkin County COVID-19 Response Epidemiologist.
On May 11, 2021, the WHO declared the Delta variant, also known as B.1.617.2, a VOC. The Delta variant was first identified in India in October 2020 and was responsible for the surge in COVID-19 cases (Figure 1) and deaths (Figure 2) in India during April-May 2021.
Figure 1. Daily Reported Cases of COVID-19 in India
Figure 2. Daily Reported Deaths from COVID-19 in India
As the Delta variant spread from Southern Asia to the United Kingdom, case counts have begun to increase in the highly vaccinated country (Figure 3). As of June 25, 2021, 65% of the population in the United Kingdom had received one dose of COVID-19 vaccine while 47% are believed to be fully vaccinated (2). Compare that to the United States where 54% have one dose and 46% are believed to be fully vaccinated (3).
Figure 3. Epidemiologic Curve of Daily Reported Cases in the United Kingdom, as of June 24, 2021
While it takes months for variants, even very transmissible variants, to cause surges in cases, the Delta variant is believed to be doubling in prevalence every fourteen days in the United States (Figure 4). In other words, if the Delta variant made up 10% of all cases of COVID-19 in a specified geographic region on June 1, by June 15, the Delta variant would be making up 20% of all cases.
Figure 4. Doubling Rate of Delta Variant in the United States
While this doubling of prevalence has not yet culminated in a noticeable country-wide increase in cases, several counties across the country have been experiencing surges in cases, believed to be caused by the Delta variant. Mesa County, for example, located just down the road from Pitkin County, has been struggling to contain an influx of cases for the past several weeks (Figure 5).
Figure 5. Weekly Cases of COVID-19 Identified among Mesa County Residents
These surges in certain counties and countries are not unexpected as vaccination rates in many places remain too low to provide significant community-wide protection. According to a study published by the Health Emergencies Programme at the WHO in June 2021, the Delta variant has been found to be approximately 97% more transmissible than the original Wuhan strain that circulated back in the early stages of the pandemic (Figure 6). In other words, if someone infected with the original Wuhan strain infected an average of three people, those with the Delta variant would infect an average of six people. Other VOIs and VOCs demonstrated increased transmissibility, but there is a clear and distinct advantage possessed by the Delta variant as it pertains to its ability to cause infection.
Figure 6. Changes in Transmissibility among Selected VOIs and VOCs Compared to the Wuhan Strain
In fact, Australian officials documented at least one case where someone had been infected simply by crossing paths with someone infected with Delta variant whereas the original Wuhan strain generally required more time paired with close proximity before most transmission occurred (4). While the world is fatigued by this pandemic that is now more than 16 months old, risk of infection with COVID-19, particularly for those who are less than fully vaccinated, remains elevated.
While the same symptoms that were associated with the original strain and early variants are COVID-19 may still be present among those infected with the Delta variant, the most commonly reported symptoms have changed. Many researchers from across the globe are reporting that headache is the most commonly reported symptom among those with the Delta variant, followed by sore throat, runny nose, and fever. Symptoms such as cough, loss of taste, and loss of smell are being less common as the virus mutates. Many have reported an “off feeling” when infected with Delta variant. Finally, more gastrointestinal issues are being reported across the world in recent months. Whereas diarrhea and vomiting were fairly uncommon in 2020, they have become slightly more common in 2021 (5).
When the two mRNA vaccines, Pfizer and Moderna, were granted emergency use authorization in the United States at the end of 2020, both companies reported remarkably high levels of efficacy. Pfizer and Moderna reported that 95.0% (6) and 94.5% (7), respectively, of individuals enrolled in their trials were protected from symptomatic infection with COVID-19, meaning they may still test positive for COVID-19 if infected, but they wouldn’t develop symptoms of the disease. Even more impressive, these two companies reported that severe illness had been averted for all those immunized with their vaccines. It is important to remember that clinical trials for these two vaccines occurred during the middle of 2020 when different variants were circulating and adherence to mask wearing, hand washing, and distancing were much greater. However, just like with flu vaccines, new vaccines are produced each year to protect individuals against the variants of the flu that experts expect to be circulating during the subsequent flu season. If the flu virus mutates enough over the summer months, after the vaccine has already been developed, then the flu vaccine will not be as effective. If the flu variants circulating during the flu season are close to what experts chose to put in the flu vaccine, then individuals will be better protected. Luckily, with SARS-CoV-2, the vaccines produced against the original strain and variants of COVID-19 will likely remain largely effective against new variants that emerge. In the case of the Delta variant, the United Kingdom has already released results from a study conducted in April demonstrating the high efficacy of both the Pfizer and AstraZeneca vaccine, which is used in the United Kingdom, but not in the United State (Figure 6).
Figure 6. Efficacy of Pfizer (BNT162b2) Vaccine & AstraZeneca (ChAdOx1) Vaccine Efficacy against the Alpha (B.1.1.7) Variant and Delta (B.1.617.2) Variant
This study found that two doses of Pfizer and two doses of AstraZeneca were approximately 87.9% and 59.8% effective against symptomatic infection with the Delta variant. However, the vaccines provided significantly reduced protection for those who only received one dose (33.2% for Pfizer and 32.9% for AstraZeneca).
While persons who are fully vaccinated are more prone to develop symptoms if infected with the Delta variant as opposed to other variants, the severity of symptoms will almost always be much less severe when compared to someone who was not fully vaccinated. In fact, the vast majority of hospitalizations and deaths occurring over the past few months have been among persons who were not fully vaccinated. A report from the Los Angeles Department of Public Health declared that in the past six months, 99.8% of COVID-19 deaths in Los Angeles were among unvaccinated persons (8).
While reports out of Israel indicate that the Delta variant does appear to be infecting individuals who are fully vaccinated, the infections do appear to be significantly less severe than among unvaccinated persons and hospitalizations and deaths do appear to be minimalized (9). The true risk remains for persons who are not fully vaccinated. Even partially vaccinated individuals may not have enough immunity to protect themselves from severe outcomes from COVID-19 infection. It is essential that everyone receive the full series of the vaccine as recommended by the manufacturer.
As more is learned about the Delta variant, better recommendations about how to best protect against spread will become available, but for the time being, the most important recommendations are as follows:
- Get fully vaccinated as soon as possible (e.g. 2 doses with Pfizer or Moderna, 1 dose with Johnson & Johnson). This is by the far the most effective strategy to prevent infection at this point in the pandemic.
- Continue to wear a mask in public, indoor spaces and around individuals who are not fully vaccinated, or where vaccination status is unknown.
- In indoor spaces, maintain social distance and spend less time interacting indoors.
- Continue to wash hands regularly and avoid touching the face.
- Get tested as soon as symptoms develop and stay home until test results are available. While less common, fully vaccinated people may be able to spread the virus to others, even if symptoms are mild.