Recently, the Chinese Center for Disease Control and Prevention published a study analyzing the real-world protection of China's domestic vaccines during the Delta and Omicron epidemics.
Source: China CdC Weekly Report
What are the conclusions of this study? What is the practical significance? Hokkaido University Master of Neuroscience, a senior medical consultant of Sheng Nuo, Weibo Science Popularization University V Zhuang Shilihe made an interpretation.
Zhuang Shilihe: This is a retrospective analysis based on all confirmed CASEs of COVID-19 Chinese mainland between 21 May 2021 and 28 February 2022.
During this period, the main variant in China changed from Delta to Omicron, and the protective power of the vaccine was assessed by comparing the proportion of patients with different severities in the unvaccinated, partially vaccinated, fully vaccinated and boosted subgroups.
There are two levels of severity here.
- pneumonia: contains moderate (i.e. common), severe and critical illness;
Severe COVID-19: Includes both severe and critical illness.
During the study period, Chinese mainland reported a cumulative total of 10,829 confirmed cases of COVID-19, of which 8,675 were caused by delta type and 2,154 by Omicron.
Of the fully vaccinated cases, of the fully vaccinated cases, 95.1% (7849 cases) were vaccinated against inactivated vaccine, 2.2% (183 cases) were vaccinated against adenovirus vectors, and 2.7% (223 cases) were vaccinated against recombinant subunit vaccines.
Detailed data can be seen in the figure, here is a simple explanation.
Source: China CdC Weekly Report
Take Delta cases in people aged 18 to 59 years.
Pneumonia developed in 363 (72.6%) of the 500 unvaccinated patients and pneumonia in 2392 of the 4233 patients who were fully vaccinated (56.5%) with a p-value of <0.01.
Using the reference of the unvaccinated group as a reference, the OR (odds ratio) of full vaccination was calculated to be 0.49, which can be considered to reduce the risk of pneumonia caused by Delta by 51%.
After intensive vaccination, the odds ratio was 0.14, which is 86% of the risk of pneumonia reduction for enhanced vaccination. In the prevention of severe disease, the risk of reduced full and booster vaccination reached 83% and 98%, respectively.
But when faced with Omicron, the vaccine's protective power drops dramatically. In the 18- to 59-year-old group, there were no significant differences in the proportion of pneumonia and severe illness, regardless of whether full or intensive vaccination.
On the one hand, this is related to the small number of cases, and on the other hand, it is also related to the small proportion of severe cases caused by Omicron. Of the 56 cases of infection with Omicron in the unvaccinated group, none were severe.
The difference was predominantly in patients >60 years of age, with the proportion of pneumonia caused by Omicron falling from 79% of the uninjugated group to 52% of the fully vaccinated group, and none of the 67 patients over the age of 60 who received the booster injection were severely ill.
Of course, the study also has some limitations, such as the cases are from all over the country, without taking into account the classification bias and differences in treatment levels across regions;
Another example is this case study, a special case-control study, so the results only reflect the relationship between vaccination and disease development risk, and can not directly measure the effectiveness of vaccines;
Finally, since more than 95% of the vaccines vaccinated were inactivated, the other two vaccines were not large enough to perform effective subgroup analyses.
Overall, this study shows that in the face of Delta, full vaccination of domestic COVID-19 vaccines can reduce the risk of pneumonia in all ages by 50% to 70%, and reduce the risk of severe illness by 70% to 80%, while the two figures of enhanced vaccination are 86% and 91% to 98%, respectively.
In the face of Omicron, full vaccination reduces the risk of pneumonia in people over 60 years of age, and intensive vaccination reduces the risk of severe illness.
The practical implication of this study is that the findings support that people aged 3 years and older without contraindications should be fully vaccinated against COVID-19, that eligible adults should receive booster injections, and that booster vaccination should be accelerated, especially in the elderly.
Curated: Ground cat
Executive Producer: Gyouza