Comparing Omicron infection with Delta and The Lancet： The symptoms of people vaccinated with more than two doses became lighter.

Many studies have revealed that the severity of diseases infected with Omicron is less severe. So, compared with Delta, what are the clinical manifestations of Omicron infection?

Recently, a large-scale study from the United Kingdom revealed that in the epidemic period dominated by Omicron, the prevalence rate of 12 symptoms of those infected with two or three doses of vaccine was significantly lower than that in the Delta epidemic period, including loss of sense of smell, change of sense of smell, sneezing, runny nose, brain fog, sore eyes, headache, fever and so on.

The researchers said that the most significant symptom difference between the two groups is the loss of sense of smell, which is the diagnostic feature of early Covid-19 infection, but now less than 20% of cases will suffer from the loss of sense of smell. The results showed that the probability of olfactory loss of infected people was only 16.7% during Omicron epidemic, while this figure was 52.7% during Delta epidemic.

In addition, during the epidemic period in Omicron, the hospitalization rate of patients was even lower, at 1.9%; During the Delta epidemic, the hospitalization rate was 2.6%.

The research is entitled Symptom Prevention, Duration, and risk of hospital admission in individuals infected with SARS-CoV-2 during periods of omicron and delta variant dominance: a prospective observatio Nal study from the ZOE COVID Study was published online in the authoritative international medical journal The Lancet on April 7th, local time.

The probability of 12 symptoms of Omicron infected people is reduced.

The main researchers of the above research are from King’s College London and Nottingham University, and three of them are consultants of the application ZOE. There are also five researchers who are employees of the application ZOE.

This study is a prospective longitudinal observation study, and the data is coming from the application ZOE, which used to be called "COVID-19 Symptom Study", and users can report infection test results and symptoms by themselves.

The purpose of this study is to compare the possibility of designated symptoms (32 symptoms monitored by ZOE) and the possibility of hospitalization between those infected in Omicron epidemic period and those infected in Delta epidemic period. Therefore, the data of two periods were compared and analyzed: from June 1 to November 27, 2021, during this period, Delta mutant was dominant in Britain, with a prevalence rate of more than 70%; From December 20th, 2021 to January 17th, 2022, Omicron mutant was dominant in Britain, and the prevalence rate was over 70%.

The study first included 63,002 ZOE users who were COVID-19-positive by PCR or LFAT from June 1, 2021 to January 17, 2022. Among them, 33,785 users tested positive during the Delta epidemic and 29,217 users tested positive during the Omicron epidemic.

After that, the study further screened the samples. Finally, the eligible participants were 16-99 years old, living in the UK, with a body mass index of 15-55kg/m2, who had been vaccinated with at least 2 doses of COVID-19 vaccine and reported symptoms. The study also matched the age, sex and vaccination times of these positive infected people according to 1:1. After matching, the total number of participants in Omicron epidemic period and Delta epidemic period decreased to 4,990 in each group.

　

Distribution of symptoms of people infected with Delta or Omicron. Paper drawings

　Through data analysis, it was found that among 4990 people in Omicron group, the most commonly reported symptoms were runny nose (76.5%), headache (74.7%), sore throat (70.5%), sneezing (63.0%), persistent cough (49.8%) and hoarseness (42.6%). Among the 4990 people in Delta group, the most commonly reported symptoms were runny nose (81.6%), headache (77.9%), sneezing (70.7%), sore throat (60.8%) and loss of sense of smell (52.7%).

The study made a detailed comparison between the symptoms of the two periods, and found that among the 32 symptoms evaluated in the study, the prevalence rate of 12 symptoms in Omicron epidemic period was significantly lower than that in Delta epidemic period, including loss of sense of smell, change of sense of smell, sneezing, runny nose, brain fog, sore eyes, headache, fever, alopecia, blisters on feet, tinnitus and dizziness.

Compared with the Delta epidemic period, the infected people in Omicron epidemic period are less likely to show at least one of the three typical COVID-19 symptoms: fever, loss of sense of smell and persistent cough. However, sore throat and hoarseness are more likely to occur during the epidemic period in Omicron.

The researchers concluded that the most significant symptom difference between the two periods was the loss of sense of smell, which was the diagnostic feature of early Covid-19 infection, but now less than 20% of cases will appear. The results showed that during the Omicron epidemic, the olfactory loss of infected people was relatively rare, only 16.7%, while this figure was 52.7% during the Delta epidemic.

In addition, the probability of many debilitating symptoms in Omicron’s case is obviously reduced, such as brain fog, burning eyes, dizziness, fever and headache.

What is the difference between the duration of symptoms and rehabilitation after the third injection?

Because all the participants in this study have been vaccinated with two or three doses of vaccine, the study also makes a comparative analysis of different vaccination States.

Regarding the hospitalization rate, the study found that compared with the Delta epidemic period, during the Omicron epidemic period, the hospitalization rate of infected people was lower (94 people in Omicron group were hospitalized, while 130 people in Delta group were hospitalized), which was similar among the two-dose vaccinators and the three-dose vaccinators. Overall, the hospitalization rate in Omicron was 1.9% in epidemic period, while in Delta epidemic period, the hospitalization rate was 2.6%.

The researchers said that the hospitalization rate of patients in Omicron epidemic period was significantly lower than that in Delta epidemic period, which supported the previous findings from South Africa and South Korea that the Omicron mutant was less severe in disease.

"We found that the hospitalization rate of Omicron infected people is 25% lower than that of Delta, which is consistent with the report of Discovery Health, a private insurance company in Johannesburg, which claims that the hospitalization risk of Omicron infected people is 29% lower than that of Delta infected people." The researcher wrote.

　

The duration of acute symptoms of Omicron infected people and Delta infected people, I is all participants; Ii is a two-dose vaccinator and iii is a three-dose vaccinator. Paper drawings

The study also analyzed the duration of symptoms of patients with different vaccination conditions.

For the participants who recovered within 21 days, the study compared the time for the acute symptoms to subside. The samples were matched Delta infected persons and Omicron infected persons, with 1530 persons in each group. The study found that, on the whole, the acute symptoms of Delta infection lasted longer, with an average of 8.89 days, while in Omicron, the figure was 6.87 days.

If divided into two doses and three doses, there is no obvious difference in the duration between the two doses. The average duration of acute symptoms in Delta group is 9.57 days, and that in Omicron group is 8.30 days. This difference is obvious among the three doses of vaccination. The average duration of acute symptoms in Delta group is 7.71 days, and that in Omicron group is 4.40 days.

The researchers said that the dramatic shortening of the duration of symptoms of infected people during the epidemic period in Omicron was related to three doses of vaccination.

In addition, the study also investigated the probability of recovery within 7 days after symptoms appeared in Omicron epidemic period and Delta epidemic period. It was found that the possibility of 7-day recovery of infected people in Omicron epidemic period was twice that in Delta epidemic period.

The researchers write that there are still some limitations in this study. Although the design of this study matches the vaccination situation (two or three doses of vaccination), it cannot match the length of time after vaccination. If compared with the matching duration after vaccination, the current research may bias the data to present the more serious clinical situation after Omicron infection. However, the researchers believe that this will strengthen the robustness of the main findings of this study, that is, the clinical manifestations of Omicron infection are not as serious as Delta.