Delta Prevalence Declines for First Time Since April as Omicron Cases Increase

The Omicron variant of COVID-19 may be proving to be a formidable opponent to Delta, which has now seen its global prevalence decline for the first time since it was categorized as a variant of concern in April.

Delta remains the dominant strain of SARS-CoV-2 worldwide, accounting for 99.2 percent of cases in the last 60 days, according to the World Health Organization (WHO). Down from 99.8 percent the last few weeks, it comes as Omicron continues to spread throughout the world, and the WHO has warned that the newer variant could overtake Delta.

"We do know Omicron is spreading fast and it has a growth advantage over Delta in some countries," Maria Van Kerkhove, COVID-19 technical lead for the WHO, said on Wednesday. "We don't have all the answers yet, but we do see Omicron is growing fast in countries where it's detected."

Of the nearly 880,000 sequences that were uploaded to GISAID, a global source of genomic data, 0.4 percent of them were attributed to Omicron. While not a significant percentage, it's higher than Alpha, Gamma and Beta, the three other variants of concern.

It's still early in the Omicron outbreak and researchers are still trying to determine the real impact of the new variant. Although it appears Omicron could hinder Delta's ability to spread, the WHO warned against reading too much into the decline in Delta's prevalence because some countries perform targeted sequencing for Omicron, which could cause them to upload fewer sequences on all other variants.

delta prevalence omicron who covid
The percentage of Delta sequences declined for the first time since April, when it was declared a variant of concern. Above, World Health Organization (WHO) Director-General Tedros Adhanom Ghebreyesus attends a daily press briefing on COVID-19 virus at the WHO headquarters in Geneva on March 11, 2020. Fabrice Coffrini//AFP/Getty Images

Some experts view Omicron overtaking Delta as a beneficial step in the pandemic if Omicron causes only mild disease. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), said it would be "best case scenario" if Omicron was highly transmissible but less severe because it could prevent the same surge in hospitalizations that the United States is seeing with Delta, which is known to cause severe disease.

However, officials from the WHO have warned that even if Omicron only causes mild disease in most people, some people will get severely ill and need to be hospitalized. Additional hospitalizations on top of an already strained system because of Delta could lead to additional deaths.

Although initial reports indicate many people have milder disease, Van Kerkhove said it doesn't mean it isn't "dangerous" because increased cases could lead to more hospitalizations.

The United Kingdom reported the first global death from Omicron on Sunday night and Van Kekhove confirmed there have been "some" others. Deaths are expected because people who were more susceptible to Delta, including those over 65 and with underlying health conditions, will still be at a higher risk of severe disease and death with Omicron.

"We have to be really careful that there isn't a narrative out there that it's 'just a mild disease,'" Van Kerkhove said. "Any dangerous virus that transmits even if it does cause more mild disease, it's better if it causes more severe disease of course, but we cannot forget that the more it spreads, the more opportunities it will change and cause severe disease."

Last week, Delta's prevalence in the United States dropped below 98 percent for the first time months. As of December 11, Omicron cases account for 2.9 percent of total sequences in the United States, and Delta is responsible for 96.7 percent. Omicron cases are significantly higher in New York and New Jersey, at 13 percent, according to the Centers for Disease Control and Prevention (CDC).

Experts are also concerned about Omicron's impact on the effectiveness of vaccines and therapeutics. It's possible the variant could decrease the effectiveness of vaccines, but officials don't expect the variant to render inoculations useless. So, they're urging people to get vaccinated if they haven't initiated their series and get their booster dose if they're eligible, as it still has shown to provide more protection than not being vaccinated at all.

Van Kerkhove also suggested that people need to start considering how much socializing they're doing and in what settings, asking themselves the question: "Should I be doing this?"

WHO officials have been pushing governments to make preparations now to handle the Omicron outbreak because once the variant is widespread, it could be too late. They've also noted that the same precautions and preparedness governments are putting in place for Omicron will be beneficial for Delta, as well.

"Omicron hasn't changed the game. The virus has gotten a bit fitter, a bit faster, we need to now up our performance to meet that challenge. But Omicron doesn't fundamentally change the nature of the challenge," Dr. Mike Ryan, executive director of the WHO's Health Emergencies Programme, said.