Omicron and Delta variants: What do we know?

Published on Monday, January 10, 2022

By: Ruth Cummins

Dr. Jason Parham, professor and chief of the Department of Medicine’s Division of Infectious Diseases, and Dr. Bhagyashri Navalkele, assistant professor and medical director of infection prevention, answer questions on what we know about the Omicron and Delta COVID-19 variants.

What do we know now about the differences between the Omicron and Delta variants?

Based on limited data available from other countries that experienced the Omicron surge before the United States, there are a few differences recognized between the two variants:

• Omicron variant is highly transmissible and can spread two to three times faster than Delta variant.
• The incubation period (time from exposure to symptom onset) is shorter for Omicron (around three days) as compared to Delta (around four to five days).
• There have been no report of major differences in symptom presentation between Omicron and Delta variants. However, people infected with Omicron variant seem to have less severe illness (risk for hospitalization, admission to ICU and death) as compared to Delta variant.
• Fully vaccinated individuals had good protection against development of severe illness with Delta variant. However, a booster dose of vaccination is needed for eligible individuals to improve antibody response and protection against severe illness from Omicron variant.

What makes the Omicron variant more contagious?

We still do not have complete understanding for higher contagiousness of Omicron variant. Based on limited studies, Omicron variant is known to have more than 50 mutations, with most being on the spike protein, which helps the virus to attach to human cells.

These mutations make the viral-cell bond stronger, resulting in easier transmission. The variant also seems to concentrate in high amounts in the upper respiratory tract, especially the nose, which may result in a higher amount of viral load being transmitted compared to previous variants.

Due to multiple mutations in Omicron variant, it evades immune response from previous COVID-19 infection and vaccination, resulting in its ability to multiply and spread among both vaccinated and unvaccinated populations.

Is it true that if you are infected with Omicron, you won’t be as sick as with a Delta infection?

Limited data available from the United States and other countries, such as the United Kingdom and South Africa, have reported less severity of illness (hospitalization, need for mechanical ventilation, death) seen with Omicron compared to Delta variant. As the United States has started to experience a surge in cases, further data from the CDC will need to confirm this finding.

If you haven’t had the booster, are you considered to be fully vaccinated?

Yes. The CDC continues to define fully vaccinated individuals as an eligible person who has completed the two-dose series of mRNA vaccine or single dose of Johnson &Johnson’s Janssen vaccine to be fully vaccinated.

You are considered up to date with vaccination if you are fully vaccinated and have received a booster shot.

I got both doses of my vaccine in early 2021. Am I still protected with antibodies?

Prior to the arrival of Omicron variant, fully vaccinated individuals were considered adequately protected against Delta and previous variants. However, studies have shown better immune response against Omicron variant among individuals who have received a booster vaccination compared to non-boosted, fully vaccinated individuals.

Booster vaccinations provide higher antibody response and better protection against development of severe disease from COVID-19. Individuals who are eligible to receive the booster should receive it without delay.

If I’ve had COVID and gotten my vaccine, do I really need a booster? Can you get COVID twice, even if you got vaccinated after having it the first time?

Yes to both questions. Re-infections have been reported among individuals who are fully vaccinated and with previous COVID-19 infection. A booster shot helps to improve immune response against highly transmissible Omicron variant and prevent severe illness.

If the Omicron variant is so contagious, should I just resign myself to getting it?

No. Although the majority of people develop mild illness, a proportion of individuals develop moderate to severe illness requiring hospitalization, ICU admission and resulting in death.

Individuals infected with SARS CoV-2 virus can spread infection to others who might not be able to fight against the infection. Furthermore, COVID-19 infection results in missing workdays. People are encouraged to protect themselves and their loved ones from getting exposed and infected with Omicron variant by using effective preventative strategies such as vaccination, hand hygiene, masking and social distancing.

If I’m infected with Omicron, is it almost certain I won’t have to be hospitalized?

There is no certainty that you would not require hospitalization if you get infected with Omicron variant. Individuals with underlying co-morbidities (cardiovascular disease, chronic respiratory disease, obesity, diabetes, underlying immunosuppression such as cancer, ongoing chemotherapy, transplant, etc.) remain at a high risk for progression to severe disease requiring hospitalization. 

The CDC now says that people with COVID-19 only have to isolate for five days instead of 10 if they don’t have other symptoms, and that they should wear a mask around other people for another five days. Why did the CDC make this change, and am I really safe around someone who has only had COVID for five days?

The CDC bases its updated recommendation on science of infectiousness timeline associated with COVID-19 illness. Based on the CDC’s statement, the highest risk for transmission is in the first and second days prior to onset of symptoms and the second and third days after.  Thus, after five days, if an individual reports improved respiratory symptoms or absence of symptoms, the risk for transmission reduces to low and everyone complying with masking around each other helps to eliminate that risk for transmission to very low risk.

If I think I have COVID and can’t find a rapid test, what should I do?

If you are unable to perform a home rapid antigen test, please go to nearest free testing location listed on Mississippi Department of Health website or any other local clinic or hospital to undergo COVID-19 testing.

Isolate away from others until your COVID-19 test result is reported.

I’ve heard that a rapid test doesn’t pick up Omicron as well as Delta. Is that the case?

Early data published by the FDA suggests that rapid antigen tests may have reduced sensitivity to detect Omicron variant, suggesting higher false negative test results. It is recommended for you to undergo RT-PCR confirmatory testing after a negative rapid antigen test if you are still symptomatic or have the likelihood of infection due to exposure.

How can I tell if I have Omicron or Delta? Does it really matter?

A positive test result does not distinguish between Omicron and Delta variant. Whole genome sequencing of isolated virus from your test sample can be sent to a specialized lab to help detect a specific variant. However, that test can take weeks to result.

Currently based on CDC’s data, more than 90 percent of circulating strains in the United States are Omicron. Health care centers have updated treatment recommendations based on the current dominant strain.