More than 193,000 Coloradans have missed getting their second COVID-19 vaccination shot within the recommended timeframe, leaving them significantly more vulnerable to the delta variant of the coronavirus than if they had gotten the booster.
That number is small compared to the almost 3 million people who are fully immunized in the state. With more than 3.2 million Coloradans having received one dose of a COVID-19 vaccine, 6% remain only partially protected, according to the state health department.
But Colorado’s faring better than the country as a whole. Nationally, almost 11% of people who got their first vaccine dose missed getting the second within the recommended timeframe, The Washington Post reported.
“These two-dose vaccines are designed to work best when people get both doses,” said Beth Carlton, an assistant professor of environmental and occupational health at the Colorado School of Public Health.
The Pfizer and Moderna vaccines require two shots to be given, ideally within three or four weeks of each other, respectively. The second dose for both vaccines may be given up to 42 days, or 6 weeks, after the first. The Johnson & Johnson vaccine requires just one dose.
Researchers have limited data on the effectiveness of the vaccines if the second dose is given later than 6 weeks after the first, according to the U.S. Centers for Disease Control and Prevention.
It’s possible that some of the 193,493 people who’ve been recorded as not getting their second dose within that time period received their booster from a vaccine provider, such as Veterans Affairs, that doesn’t report to Colorado’s immunization database or did so out of state, according to a spokesperson with the Department of Public Health and Environment.
It’s unclear why people didn’t get their second dose, but it is on vaccine providers to make the logistics of getting the shots accessible, Carlton said. Typically, COVID-19 vaccine providers schedule appointments for a second shot when a person gets their first, according to the state health department.
The agency said it is reaching out to people who are overdue for their second dose, including via phone calls, texts and emails.
Colorado has seen a slowdown in the pace of COVID-19 vaccines in recent months and the state’s incentive lottery did not spur a significant increase in people getting the shots. During the past two weeks, the state has administered fewer than 100,000 doses per week — a level not seen since the shots first became available in December.
As demand has fallen, public health officials have shut down the state’s mass-vaccination sites, including at Ball Arena in Denver.
Getting Coloradans fully vaccinated is even more critical now that the more contagious — and potentially more severe — delta variant has become the dominant strain of the virus spreading in the state.
It’s estimated by the state’s COVID-19 modeling team that 90% of new infections in Colorado involve the delta variant and only 52% of the state’s total population has immunity based on vaccinations and infections.
Generally, one dose of the Pfizer or Moderna vaccines is about 50% effective against symptomatic infection from the coronavirus. But with the delta variant, the efficacy drops to about 35%. By comparison, the efficacy of the vaccines increases to about 90% after the second dose, Carlton said.
“Those people who have a single dose are vulnerable to getting symptomatic infection,” she said, adding, “The vaccines are highly effective against hospitalization for delta or alpha (variants).”