Influenza viruses often mutate, is flu vaccine really effective?
Influenza viruses often mutate, is flu vaccine really effective? The flu virus mutates every year, and the flu vaccine produced every year has little change. Sometimes, like last year’s flu vaccine, it has no effect on the new flu. Is that right?
Let us take a look at what efforts WHO and countries around the world have made to prevent influenza pandemic. First, let us understand the influenza virus.
01. Structure and Classification of Influenza Virus
Influenza viruses belong to the Orthomyxoviridae family and are single-stranded negative-strand segmented RNA viruses. According to virus nucleoprotein and matrix protein, it is divided into four types: A, B, C, D (or A, B, C, D). Among them, influenza A viruses can be divided into multiple subtypes according to the protein structure and gene characteristics of hemagglutinin (HA) and neuraminidase (NA) on the virus surface. At present, there are 18 (H1-18) and 11 (N1-11) subtypes of HA and NA, respectively.
In addition to infecting humans, influenza A viruses are widespread in animals, such as poultry, pigs, horses, seals, whales and minks. Influenza B is divided into Victoria strain and Yamagata strain, which can circulate in the population. Recent data show that seals can also be infected. Influenza C virus infects humans, dogs and pigs and only causes sporadic cases of upper respiratory tract infections. Influenza D virus mainly infects pigs and cattle, but has not been found to infect humans. Currently, the viruses that cause seasonal influenza epidemics are the H1N1, H3N2 subtypes of type A and the Victoria and Yamagata strains of type B viruses.
Among the three influenza viruses that infect humans, type A influenza virus is the most harmful. It often appears in the form of outbreaks in the population and can cause a global influenza pandemic. The epidemic scale of influenza B virus is much smaller than that of influenza A virus, and influenza C virus rarely causes epidemics.
02. How does the flu virus mutate?
The frequency of influenza virus mutation is rapid, and new epidemic strains occur every year, and its mutation mainly occurs in two ways: antigenic drift and antigenic shift.
Antigenic drift occurs within a certain subtype, such as a point mutation in HA or NA, which is a quantitative change, that is, intra-subtype variation, which can cause small-scale epidemics. Antigenic shift refers to the appearance of a completely new HA or NA subtype, which is a qualitative change.
Because influenza viruses, especially influenza A viruses can infect humans and animals, viruses can spread across populations. When two different viruses infect a cell at the same time, the genome fragments of the virus may randomly exchange with each other, causing gene rearrangement to form new subtypes. , Which is why influenza viruses are prone to mutation. The population generally lacks immunity to the mutated new subtype influenza virus, which often causes a larger epidemic, or even a worldwide epidemic.
In addition, studies have shown that mutations in the internal proteins of influenza viruses can also cause changes in the virulence of influenza viruses or make the virus evade the recognition of the host’s immune system, thereby increasing the chance of virus infection.
03. Why does flu virus mutate and cause epidemic?
Because influenza viruses often mutate, when a mutant strain becomes popular, the antibody level of the population increases accordingly, and the epidemic strain will be suppressed, while another new mutant strain will gradually become an epidemic strain; when the antibody level of the new mutant strain in the population increases, Another new variant will appear, and the epidemic will happen again. Antigens continue to drift or change, and susceptible populations change, leading to repeated epidemics. Therefore, it is necessary to replace the vaccine strains every year according to the epidemic situation, and control the spread and epidemic of influenza among the population through timely vaccination.
04. How does the flu vaccine deal with the constantly mutating flu virus?
The main factor affecting the preventive effect of influenza vaccine is the antigenic matching of influenza virus epidemic strain and influenza vaccine strain. The higher the matching degree, the better the effect. However, in years when the matching between the two is weak, although the effectiveness of the flu vaccine will be reduced, it can still bring substantial effects.
To match the constantly mutating influenza virus, the World Health Organization (WHO) generally announces vaccine recommendations for the next influenza season in the northern hemisphere in February each year. The scientific basis is that the WHO Cooperation Center and the Global National Influenza Center form a powerful monitoring network. Through the monitoring results of hundreds of national influenza centers, the influenza strains of the next epidemic season are screened out and recommended to influenza vaccine manufacturers to prepare vaccines. Three of the virus strains circulating in the northern hemisphere announced by the WHO this year have been updated compared to last year, and two of them are from Maoming, Guangdong and Hong Kong. It can be said that the flu vaccine has been monitoring and hunting down flu viruses that are constantly changing their faces.
05. Time limit for influenza strain monitoring and vaccine production
Because influenza vaccine production generally needs to be completed within 6 to 8 months, and influenza vaccination in the northern hemisphere should be completed from October to December every year. The time required to collect and evaluate relevant data in order to propose the best vaccine composition must be balanced with the vaccine production time. If you make a recommendation too early, you may miss important antigenic variants; if you make a recommendation too late, the production of the vaccine will be delayed.
In addition, in addition to collecting, analyzing and monitoring data, the production of vaccine candidate strains requires accumulation of experience, and preparation of standards for new vaccine components also takes time. To this end, on the basis of annual monitoring, WHO will promptly inform the manufacturers of global influenza surveillance information. Once the vaccine strains that need to be changed are determined, the drug regulatory authorities and manufacturers will conduct research on the antigens of the changed strains to check whether they are suitable. In production, high-yield reproducing strains have also begun to be prepared. Under normal circumstances, the protective effect of influenza vaccine can reach about 75%, and the protective effect of live attenuated influenza vaccine in children is 73% to 93%.
06. How does the flu vaccine work?
In essence, influenza virus and influenza vaccine are twin brothers, because they are from the same source and look alike. If the flu virus is likened to a devil who goes crazy and specializes in doing bad things; the flu vaccine is a weak chicken that has been specially treated to remove the devil and has no pathogenic appearance. Let this weak chicken mix with the strong immune system of the human body. Familiar, mobilize the emergency response capabilities of the human immune system to play a defensive role through close combat.
The entire battle process is: After vaccination, the body’s immune system is stimulated to produce antibodies. If you encounter influenza virus infection, these antibodies will target and accurately neutralize these viruses, which is equivalent to opening a lock with a key. The purpose of neutralization is the combination of antibodies and viruses, so that the virus loses the ability to infect. The result of neutralization is to form an antigen-antibody complex and be cleared by the immune system to ensure that the body is not sick.
It can be seen that in the entire process of anti-virus and anti-infection, the immune system produces antibodies that are very sacrificial. By combining with the influenza virus and killing them together, it achieves the purpose of preventing influenza.
07. The preventive effect of influenza vaccine is remarkable
Since the 20th century, there have been 5 global influenza pandemics, and many people have lost their lives. The most serious one was the “Spanish flu” in 1918. About 50 million people died, which was several times the number of deaths in the First World War (more than 10 million people). Few infectious diseases can be as persistent and widespread as influenza. Affect the global economy and human health. Today, 100 years later, people have effectively controlled the influenza pandemic by vaccinating influenza. Data shows that influenza vaccine has a 53% preventive effect on influenza-like diseases in elderly people ≥ 60 years old. Influenza vaccination can also reduce the incidence of influenza-related complications in the elderly and reduce influenza-related hospitalizations and deaths.
08. Development direction of future influenza vaccine
Due to the rapid variation of influenza vaccines, in order to cope with the influenza pandemic, researchers are currently working on a general influenza vaccine that can not be affected by the matching degree of the surface antigens of the vaccine strain and the epidemic strain, and can induce a broad-spectrum and long-lasting immune effect. , Become the direction of future influenza vaccine research and development.
During the World Influenza Conference on November 1 this year, Australian expert Kanta Subbarao also mentioned the significance and value of studying influenza universal vaccines: through the development of universal influenza vaccines covering multiple subtypes, multivalent antigens and cross-immunity, it is used to cope with continuous influenza. Mutated influenza virus to achieve the purpose of preventing and controlling influenza pandemic.
(source: yimiaoquan of Influenza viruses often mutate, is flu vaccine really effective?)