Recently, the research team of Doha Cornell Medical Center published the research results entitled “Effectiveness of influenza vaccination against SARS-CoV-2 infection among healthcare workers in Qatar” on the medRxiv. The study found that people who received the flu vaccine were nearly 90% less likely to develop a new coronary disease in the coming months than those who had not recently received the flu vaccine.
The study, led by infectious disease epidemiologist Laith Jamal Abu-Raddad, analyzed the health records of 30774 health workers in Qatar between September 17, 2020, and December 31, 2020 (before COVID-19 and after influenza vaccination). The median age of the data sample was 36 years old, while that of the control group was 35 years old. The median duration between influenza vaccination and PCR testing was 43 days.
Through the analysis of the data results, the following conclusions are drawn:
- The protective effect against novel coronavirus was 29.7% after 14 days of influenza vaccination.
- The effectiveness of influenza vaccine against any serious, critical or fatal symptoms of COVID-19 was 88.9%.
- Influenza vaccination is associated with a significant reduction in the risk of SARS-CoV-2 infection and the severity of COVID-19.
- The protective effect of influenza vaccine against COVID-19 is about six weeks.
Günther Fink, an epidemiologist at the University of Basel in Switzerland, said: “Our previous studies in Brazil have shown that influenza vaccination is associated with a reduced risk of death in patients with COVID-19. The Qatari analysis reduces the likelihood that other studies that find the same link are just a fluke. “
Mihai Netea, an infectious disease expert at the University of Radboud said: “This is an important piece of evidence that influenza vaccines are associated not only with a reduction in SARS-CoV-2 infection but also with disease severity. This observation strongly suggests that the protective effect is real. However, I do not believe that the protective effect of the influenza vaccine against COVID-19 lasts very long, perhaps as little as six months to two years. It is not entirely clear why an influenza vaccine consisting of inactivated influenza viruses also protects against COVID-19 pneumonia. Vaccines train the immune system to recognize specific pathogens, but they also enhance broadly acting antiviral defenses.”
Similarities and differences between influenza virus and novel coronavirus
Viruses are non-cellular organisms that parasitize within living cells and proliferate in a replicative manner. Different viruses invade cells in different ways. However, most of them require cellular internalization by binding to specific receptor proteins or lipid structures on the cell surface to initiate the invasion program and infect the host cell. Therefore, uncovering the specific processes and mechanisms by which viruses bind and internalize invading cells can help develop targeted drugs or vaccines at the source.
Influenza virus can be divided into four types A, B, C and D, according to the antigenicity of nucleoprotein. Human influenza is mainly caused by influenza A and B viruses, influenza C virus only causes unobvious or mild upper respiratory tract infection in humans, and the host of influenza D virus is mainly cattle. Influenza virus, which belongs to orthomyxoviridae, is an envelope virus, which is embedded with three kinds of membrane proteins: Hemagglutinin (HA), Neuraminidase (NA) and Membrane protein 2 (M2). HA exists in the form of homotrimer.
HA is hydrolyzed to form a light chain and heavy chain, in which the heavy chain is responsible for the binding of the virus to the cell, while the light chain assists in the semi-fusion of the viral membrane and the endocytosis membrane. NA is a mushroom-shaped tetramer glycoprotein that has the activity of hydrolyzing sialic acid and can help the virus released from host cells. Membrane protein 2 acts as an ion channel and regulates pH in the membrane. In addition, the matrix protein 1 forms the shell skeleton of the virus, which binds closely to the outermost envelope of the virus, protecting the virus core and maintaining the virus spatial structure. The genetic material of the virus is a viral ribonucleoprotein complex formed by folding a single strand of negative-strand RNA and a nucleoprotein.
Coronavirus is a kind of virus that exists widely in nature. It only infects vertebrates and was first isolated from chickens. The coronavirus particles are about 60-220 nm in diameter and have three glycoproteins: spike glycoprotein, small envelope glycoprotein, membrane glycoprotein and a few hemagglutinin glycoproteins. The nucleic acid of coronavirus is a linear single strand positive strand RNA, 5′ with methylated cap structure and a polyA tail at the 3′ end, which is similar to eukaryotic mRNA and can act as a translation template by itself. The whole genome is 27-32 kb long, which is the largest known RNA virus at present.
The International Committee for virus Classification divides it into four genera, namely, α, β, γ and the new hypothetical δ coronavirus genus. Novel coronavirus is a β-coronavirus with strong infectious ability. At present, the whole genome sequence of novel coronavirus and the proteins that virus binds to cells have been detected, but the mechanism of its invasion and infection is not clear.
Influenza virus and SARS-CoV-2 are adsorbed to the cell surface by ligand receptor binding, and HA and S protein are activated to form two subunits by intracellular proteolytic enzymes, which are respectively responsible for the binding of virus and host cells and mediating membrane fusion. After influenza virus binds to the cell receptor, it needs the participation of a variety of cytokines to achieve endocytosis, and studies have shown that novel coronavirus may also use some intracellular adsorption-promoting factors, such as binding to cellular glycoproteins, to enhance its infectivity.
There are some similarities between influenza virus and novel coronavirus in the mechanism of action on cells, so it is a potential way to use the research method of influenza virus to study the interaction between novel coronavirus and cells. it is not difficult to understand the protection of influenza vaccine against COVID-19.