Omicron variant vs. Delta: what are the differences?

Omicron VS. Delta

Omicron variant vs. Delta: what are the differences?


First identified in South Africa in November 2021, the SARS-CoV-2 variant, B.1.1.529 (the Omicron variant), has now been detected in almost every country. It is believed that Omicron may spread more easily than other variants, including the Delta variant, as a result of its increased transmissibility and its ability to evade immunity conferred by past infection or vaccination (i.e. immune evasion). Despite the fact that the severity of the illness and death associated with Omicron is still under research, early data suggest Omicron may not make people as ill as prior variants. Even so, we should not overlook the impact of Omicron as the sheer volume of people testing positive will pile more pressure on the already overburdened health care systems.


Viral mutation and spike protein

 A viral mutation is a change in the genetic sequence and a new variant may have one or more mutations that differentiate itself from the original virus. Variants of COVID-19 may have different characteristics. For example, the spike protein of the Delta variant has more efficient cell-cell fusion kinetics as compared to the original Wuhan strain. All variants will be monitored by scientists and may be classified as variants being monitoredvariants of interestvariants of concern and variants of high consequence. These classifications are based on transmission rates, the severity of symptoms, how the variant responds to treatments, and how well vaccines protect against the variant. Currently, only two variants of COVID-19, Delta and Omicron, are classified as variants of concern by the United States.


The spike protein is the primary target of vaccine-induced immunity. The Omicron variant is characterized by multiple spike protein mutations across all spike domains as compared to other major variants. Some of these mutations are concerning because they are known from other variants to be associated with reduced susceptibility to available monoclonal antibody therapeutics or reduced neutralization by convalescent and vaccinee sera. Also, analysis of these changes indicates that Omicron is likely to have increased transmissibility compared to the original COVID-19 virus.


In a nutshell, it is expected that Omicron may spread faster than previous variants and may cause breakthrough infections.


Omicron variant spreads about 70 times faster than Delta


According to a study from the University of Hong Kong, the Omicron variant infects and multiplies 70 times faster than the Delta variant and the original COVID-19 variant in human bronchus. This may be the reason why Omicron can transmit faster among people than previous variants. Their study also showed that the Omicron variant replicated less efficiently in the lungs than the original COVID-19 variant, which may be an indicator of lower disease severity. However, the leader of the research team commented that “by infecting many more people, a very infectious virus may cause more severe disease and death even though the virus itself may be less pathogenic. Therefore, taken together with our recent studies showing that the Omicron variant can partially escape immunity from vaccines and past infection, the overall threat from Omicron variant is likely to be very significant.”


Omicron variant might help defend against Delta


According to a small study published by South African scientists from the website of Africa Health Research Institute, people who have recovered from an Omicron infection may have increased immunity against the Delta variant. One possible explanation is that Omicron infections simply roused the existing immunity in volunteers, provided either by vaccinations or previous infections. Another possible explanation is that the antibodies produced by Omicron can also fight other variants such as Delta. As a result, Omicron may displace the Delta variant.


Some scientists who did not participate in the study said that the findings were consistent with what happened in England and Connecticut – that the number of Omicron cases rose exponentially while the number of Delta cases fell. A public health researcher at the Yale School of Public Health told the New York Times that “[t]his suggests to me that omicron is outcompeting delta for susceptible individuals, leaving them less susceptible to delta in the aftermath and driving down delta cases.”


This paper was published as a preprint on MedRxiv, and is yet to be peer-reviewed by other scientists.


Is the Omicron variant more contagious?


Yes, early reports show that the Omicron variant may spread more easily than the original COVID-19 variant. Anyone infected with Omicron can spread the virus to other people, even if they are vaccinated or do not have any symptoms. That being said, vaccination and other preventive measures such as wearing a mask and keeping social distance are still critical in preventing the spread of COVID-19, regardless of the types of variants.


Omicron variant vs. Delta: Is there a difference in symptoms?

So far there is no information to suggest that the Omicron variant causes different symptoms from other COVID-19 variants. Some early findings suggest that there is a reduced risk of hospitalization for Omicron compared to the Delta variant. It seems that some people with Omicron infections develop similar symptoms of a cold, including a sore throat, runny nose and a headache, whereas people infected by previous variants tend to have classic symptoms such as a continuous cough, a fever or high temperature and a loss or change to smell or taste. The symptoms caused by the Omicron variant have often been described as “mild”. 


On the other hand, it is also common for people with Delta infection to develop a runny nose, sore throat and a headache. As to severity of illness, Delta may cause more severe cases than the other variants, whereas the current severity of illness and death associated with Omicron is still unclear.


It is important to note that both Delta and Omicron (or any other variants) are essentially the same COVID-19 virus and that means while certain symptoms may appear more prominent or noticeable in one variant, the symptoms of all COVID-19 variants are still similar, spanning from mild to severe illness.


Damage differences

 Several studies found that Omicron does not damage lungs as much as Delta and other previous variants of COVID-19 and evidence indicates that Omicron is more likely to infect the throat (the upper respiratory tract) than the lungs. By contrast, previous variants often caused lung scarring and serious breathing issues. This may be the reason why people infected with Omicron tend to have less severe symptoms and the transmission rate is higher (a virus will be more transmissible if it replicates more in the throat and the upper respiratory tract). These studies are still under peer review.


Although early data show that Omicron appears to be milder and those infected are less likely to need treatment in hospitals, we should remember that all COVID-19 variants can cause severe symptoms or death. The World Health Organization (WHO) warns that the Omicron variant should not be dismissed as “mild” as the sheer number of cases caused by increased spreading rate could once again overwhelm unprepared health systems, which in turn can result in more deaths.


Are children more likely to contract the Omicron variant?

According to the United Nations International Children’s Emergency Fund (UNICEF), currently there are not enough information to confirm whether children are more likely to contract the Omicron variant and research is still ongoing into Omicron’s transmissibility. In general, people who are not vaccinated and are mixing socially are more susceptible to contracting COVID-19.


How can I protect myself and my family against the Omicron variant?

 Getting vaccinated is still the best way to protect people from severe illness, hospitalizations and death brought by COVID-19, according to the US Centers for Disease Control and Prevention (CDC). It is recommended that everyone aged five years and older should be fully vaccinated and that people aged 16 years and older should get a booster shot after completing their primary COVID-19 vaccination series.


The CDC continues to recommend wearing a mask in public indoor settings and in areas of substantial or high community transmission, regardless of vaccination status. Many research studies have proven that mask wearing is an effective way to protect the wearer and impede the transmission of all COVID-19 variants. Other preventive measures include keeping social distance, avoid poorly ventilated or crowded places and perform personal hygiene such as washing your hands frequently.



 As of 20 January 2022, the Omicron variant had been identified in more than 170 countries. It is believed that the rapid growth rate of Omicron infections is a result of its increased transmissibility and its ability to evade immune protection conferred by vaccines or past infection. Although early data suggest a lower risk of severe disease and death than previous variants such as Delta, its high transmissibility has led to a significant increase in hospitalization and piled pressure on the health care systems in many countries.


So far, getting vaccinated is still the best way to protect yourself from potential severe illness, hospitalization and death. It is also important to reduce the risk of exposure to the virus by practicing preventive measures such as wearing a mask, keeping social distance, avoiding crowded places and washing your hands frequently.



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  2. Africa Health Research Institute. (2021, December 28). Omicron infection enhances neutralising immunity against Delta.
  3. Classification of Omicron (B.1.1.529): SARS-CoV-2 Variant of Concern. (2021, November 26). World Health Organization.
  4. COVID-19: Don’t underestimate Omicron, WHO chief warns. (2021, December 14). UN News.
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  6. HKUMed finds Omicron SARS-CoV-2 can infect faster and better than Delta in human bronchus but with less severe infection in lung. (2021, December 15). News | HKUMed.
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  8. Omicron Variant Appears to Cause Less Damage to Lungs, Studies Say. (2022, January 3). WebMD.
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  10. Potential Rapid Increase of Omicron Variant Infections in the United States. (2021, December 20). US Centers for Disease Control and Prevention.
  11. Roxby, B. P. (2022, January 4). Omicron: How do I know if I have it? BBC News.
  12. Science Brief: Omicron (B.1.1.529) Variant. (2021, December 2). US Centers for Disease Control and Prevention.
  13. Stay Up to Date with Your Vaccines. (2020, February 11). US Centers for Disease Control and Prevention.
  14. Tapper, J. (2022, January 2). New studies reinforce belief that Omicron is less likely to damage lungs. The Guardian.
  15. What we know about the Omicron variant. (2022, January 14). UNICEF.
  16. What You Need to Know About Variants. (2021, December 13). US Centers for Disease Control and Prevention.
  17. Zimmer, C. (2021, December 29). Omicron Variant May Help Beat Delta, Study Suggests. The New York Times.

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