The omicron variant remains a concern as Americans and others prepare for holiday travel and get-togethers. Although the data available on transmission, vaccine effectiveness, and severity of the disease is still in flux, here are some things we know so far.
Transmission
Omicron quickly became the dominant variant in America. According to the Center for Disease Control & Prevention, the country received its first confirmed case on December 1. Omicron was responsible for 59% of all new cases by the week ended December 25. (See “Variant Proportions.”)
This seven-day average number of cases in the U.S. due to any variant has risen to about 80,000 on November 29 and 135,000 on December 19. Factcheck.Org
According to current data, Omicron is expected to outpace Delta in areas where community transmission occurs. On December 17, the World Health Organization stated that Omicron was identified in 89 countries and “consistent proof” that this variant has a “substantial growth advantage” over Delta. The WHO said in a technical brief that “it is spreading significantly faster in countries with the documented transmission, with a doubling time of 1.5-3 days.” “Omicron is rapidly spreading in countries with high populations immunity, but it’s not clear if the rapid growth rate or immune evasion are to blame.
In an earlier story, we mentioned that scientists were worried about this variant being transmitted easily. Several mutations in the genome, such as those at the furin cleavage sites, have been associated with increased transmissibility. This is the spot on the virus’s spike protein removed by enzyme furin to activate it and make it ready for entry into cells.
Researchers at Hong Kong University released information on a lab study that was not peer-reviewed on December 15. They found that the Omicron variant multiplied in the respiratory-tract tissue 70 percent faster than the original SARS/CoV-2 within the first 24 hours. According to a press release, this could explain why Omicron might transmit more quickly between people than the previous variant.
Researchers with the Ragon Institute in Massachusetts & others posted a not-yet-peer-reviewed study on December 14 that found an omicron pseudovirus tested in the lab was “more infectious” than Delta or the original versions of the virus due to a more efficient ability to attach to the ACE2, the human receptor this the virus uses to gain entry into cells. Omicron was twice as infective as Delta, according to the study.
Some evidence suggests that Omicron may have a shorter incubation time — the period between the initial symptoms and exposure to the virus — than other variants. A case study of Omicron spreading at a Norwegian company Christmas party, where 74% of the attendees had confirmed or probable cases, found that the incubation time was zero and eight days. However, the median was three. According to Eurosurveillance, the median incubation time for the infection was three days. This is shorter than previous reports of Delta and other non-Delta SARS/CoV-2 cases (4.3 and 5.0 days, respectively).
Like many variants, research on the incubation period is necessary. If it’s shorter, the virus can move quickly from one person to another. According to The Atlantic, on December 20, a shorter incubation time is crucial in coronavirus variant spread. The sooner someone becomes contagious. The faster an outbreak will spread.
Vaccine effectiveness and reinfection
However, laboratory and real-world tests have shown that COVID-19 vaccines do not work as well against Omicron. However, booster doses offer more excellent protection, and primary doses may still provide some protection against severe illnesses. This is only preliminary data and is based on small samples and estimates. More research is required.
Researchers from South Africa and others have shown a 41-fold decrease in the neutralizing power against Omicron among 12 people with the Pfizer vaccine. It was also found that five out of six people with hybrid immunity, which is two doses of vaccine and a prior infection, had “relatively low neutralization titers against omicron.
Based on PCR-confirmed cases from England between November and December, the Imperial College London COVID-19 Response team calculated that the risk for reinfection with the omicron variation is 5.4x higher than the risk for reinfection with the delta variant. The vaccine effectiveness against symptoms after two doses (Pfizer/BioNTech/AstraZeneca) of the vaccine was between 0% to 20% in the study. According to the survey, a third booster dose of vaccine would provide 55% to 80% protection from symptomatic infections. It has not been peer-reviewed.
Based on 211,000 PCR-positive test results in the three weeks preceding the omicron spread, a non-peer-reviewed study by South Africa’s largest insurance company found a greater risk of reinfection than with other variants. It was also found that vaccine effectiveness against severe diseases that required hospitalizations due to the omicron surge was 70%, with two doses of Pfizer/BioNTech vaccines and 33% against infection.
Comparatively, the mid-2020 wave had an estimated 80% efficacy against infection.
According to the press release, the preliminary information could change over time and maybe affected due to the high levels of antibodies found in South Africa’s population. South Africa’s vaccination rate is low, but it has high rates of the previous infection. Consequently, most people have some immunity to the virus.
The WHO stated that there are insufficient data and no peer-reviewed evidence to support Omicron’s vaccine effectiveness or efficacy. The WHO advises caution when interpreting preliminary data from South Africa or England because of possible “selection bias” in the studies and “relatively low numbers.”
Pfizer reported on December 8 that preliminary laboratory tests had shown that blood samples were taken from the two-dose series only experienced “significantly decreased neutralization titers.” However, the third booster dose resulted in a 25-fold rise in neutralizing antibodies for Omicron. After the booster, the amount of neutralizing antibodies against the original, nonmutated strain was the same as the levels after the first two doses.
Pfizer stated that two doses of the omicron variant vaccine might be sufficient to protect against severe illness. This is because vaccine-induced T cells can still recognize it. There means that people who have been vaccinated will build a robust immune response and not be affected by severe Disease.
The laboratory tests showed that sera were taken from 19 people who had received their second dose one month earlier and 20 who had just received their booster dose one month earlier.
Moderna announced on December 20 that 20 booster recipients had reported lab results showing a 37-fold increase of the levels of neutralizing antibodies against Omicron after receiving the vaccine’s authorized booster dose. This was compared to the story before the booster. Stephane Bancel (CEO of Moderna) called the results “reassuring.”
Moderna and Pfizer both stated that they continue to test an omicron-specific vaccine if needed.
Moderna lab-tested blood samples were taken from patients 29 days after receiving a booster dose. A half-dose from the original series is all that is allowed for the authorized booster. Moderna also tested sera taken from patients who received a champion containing the same mRNA dose for the initial shots. This resulted in an 83-fold increase in neutralizing antibodies. It also tested boosters that have multiple mRNA mutations. These boosters were similar to the approved doses in terms of neutralizing antibodies.
Johnson & Johnson has yet to release information about laboratory tests for its vaccine against Omicron.
Researchers at Ragon Institute also examined the ability of sera taken from over 200 people to neutralize pseudoviruses Omicron. The Ragon Institute researchers found that the sera of those vaccinated with Moderna, Pfizer, and Johnson & Johnson vaccines failed to cancel Omicron. However, those who received a booster of an mRNA vaccination showed “potent neutralization” comparable to the levels seen with the original virus.
The gravity of the Disease
Anecdotal evidence and preliminary studies suggest that Omicron may cause less severe diseases than other variants. However, the virulence of Omicron is still being investigated.
Omicron has also been linked to deaths.
On December 17, the WHO stated that additional data were needed to determine the severity of the disease. However, it was clear that the increase in cases could pressure the health care system. Tedros Adhanom Gebreyesus, WHO’s director-general, stated that Omicron could cause less severe diseases, but the sheer volume of cases could overwhelm unprepared health care systems.
According to a press release, the Hong Kong University study showed that the omicron variation reproduced rapidly in respiratory-tract tissues. Still, it multiplied ten times slower in human lung tissue than its original coronavirus. This could indicate a lower degree of Disease.
However, one researcher cautioned that the severity of the disease depends on how the immune system reacts to infection. This is not just dependent on how the virus replicates in tissues. “It’s also worth noting that a highly infectious virus can infect more people than the virus itself, which may lead to more severe illness and death, even though it may be less dangerous,” Dr. Michael Chan Chiwai of the Centre for Immunology and Infection at Hong Kong Science and Technology Park said.
Initial evidence from Imperial College London did not show that Omicron caused more severe cases than Delta. However, in the second report of cases between Dec. 1 and 14, researchers discovered evidence of a lower risk of hospitalization than Delta. These included 20% to 25% for any hospitalization and 40% to 45 percent for one-day or more hospitalizations or those who were “admitted.”
According to the U.K. Health Security Agency, there were seven deaths and 85 hospitalizations associated with Omicron between December 16 and December 16.
Early data from Scotland shows a two-thirds decrease in hospitalizations from Omicron compared to Delta. The data were released on December 22 and was not peer-reviewed.
South Africa’s largest insurance company found a significantly lower risk of severe diseases in the country.
This risk of hospitalization due to Omicron was 29% lower than for an outbreak in mid-2020. This data was adjusted for vaccination status. 41% of positive cases were adults who had received two doses of Pfizer/BioNTech vaccinations.
The CDC released early information on 43 cases of Omicron in the U.S. between Dec. 1 and 8. It stated that 34 of those people had been fully vaccinated, 14 having received a booster. Six of the six people were previously infected with SARS-CoV-2. The symptoms were mild and included a runny nose, cough, fatigue, congestion, and headaches. One person who was vaccinated spent two days in the hospital. As of December 10, there were no reported deaths from these cases. The CDC stated a lag between infection and more severe outcomes.
A Houston man infected by the omicron variant of the Disease died on December 20. This is the first known American death from the variant. In a press release, Harris County Public Health stated that the victim was between 50 and 60 years old and had been infected previously with SARS-CoV-2. Some other health issues put him at greater risk for a severe infection.
See our December 3 story, “Q&A about the Omicron Variant,” for more information on Omicron and its initial reports.
Updated December 28: This story has been updated with the CDC’s most recent estimate of omicron prevalence in the United States. The CDC estimated that the omicron variant accounted in the U.S. for 59% of cases during the week ending December 25.
The agency significantly revised its previous estimate for the week ending December 18, when it issued its latest estimation. This story also includes the initial assessment of 73% by the CDC. The CDC now believes that there was 22.5% omicron in that week.
