Author: Wu Simin

This spring's flu season is passing its peak, but the autumn and winter flu season in the second half of the year remains a challenge.

According to the latest surveillance information from China Disease Control, the level of influenza activity began to increase in early February 2023, and the upward trend was obvious after the end of February, and it had reached a peak by mid-March. While overall levels remain high, several provinces have been monitored to have seen peak inflection points in influenza activity and begin to decline.

Influenza, is the abbreviation of influenza, which belongs to class C infectious diseases in China, that is, the diseases that are classified as the lowest level of management in the type of statutory infectious diseases.

However, the epidemic of seasonal influenza can also bring a greater burden of disease. According to WHO estimates, seasonal influenza causes about 300 million ~ 500 million severe cases every year. Jiang Rongmeng, vice president of Beijing Ditan Hospital, previously wrote that seasonal influenza causes 5%~15% of infected people, more than 50,20 medical patients and <>,<> excess deaths in southern and northern China every year.

Wang Dayan, director of the National Influenza Center of the Institute of Virus Control and Prevention of Disease Control and Prevention, recently said that from the perspective of the epidemic situation, this spring's influenza is at a "high level" epidemic but has not caused a "pandemic". However, from the perspective of autoimmunity, because influenza A and B have not caused a high level of epidemic nationwide in the past three years, the public has generally reduced their awareness of influenza prevention and control, and the influenza vaccination rate is low, resulting in a decrease in the pre-existing immunity of the population, especially children, to influenza A (H3N1) virus. After the implementation of "Class B and B tube" for new coronavirus infection in early 1, the flow of international and domestic personnel and social activities became normalized, and influenza activities dominated by the H2023N1 subtype caused the peak of influenza in China's spring.

"At the end of February 2023, influenza activity rose rapidly, lagging by about 2 months compared to the previous normal flu season." Wang Dayan.

Jin Dongyan, a virologist and professor at the School of Biomedical Sciences at the Li Ka Shing School of Medicine at the University of Hong Kong, told First Finance and Economics that due to the lag of the seasonal flu, there is not much "respite preparation" left for the autumn and winter influenza season in the second half of the year.

He said that it is not realistic for influenza vaccines to be included in the national immunization programme system in just a few months, and it is not realistic to significantly increase the production capacity of influenza vaccines, considering the scrapping rate of vaccines. Public health strategies, then, need to focus more on increasing influenza vaccination rates among immunovulnerable populations. At the same time, surveillance systems need to be improved to accurately assess the true risk of disease and respond early.

"A more scientific 'mask strategy' depends on more accurate monitoring"

"Is wearing a mask a blessing or a curse?"

With the change of the new crown epidemic and prevention and control strategies, in the winter and spring seasons of the northern hemisphere this year, influenza and other respiratory diseases have seen different degrees of "retaliatory rebound" in many countries, which has also attracted the attention of scholars from various countries to this issue.

The influenza surveillance data of disease control departments of many countries show that the 2022/2023 winter-spring influenza epidemic season has two characteristics: "lag" and "high level epidemic". Some studies believe that these two characteristics are closely related to non-pharmaceutical interventions (NPIs) such as "wearing masks".

Specifically, "lag" is not only related to the new crown virus infection to change the host's susceptibility to other viruses, but also related to the fact that most people will consciously stay at home, stagger peak hours or stop work after infection with the new crown virus, and most primary and secondary schools and childcare institutions are on holiday, which reduces the risk of crowd gathering and virus transmission; The "high level of epidemic" is inseparable from the non-pharmaceutical interventions (NPIs) such as masks that last for three years, and the population is low-exposure to pathogens such as influenza for a long time, reducing autoprotective immunity and affecting specific immune responses, forming an "immune debt".

According to a research article published in The Lancet, public health and social measures during the 2019/2020 influenza season reduced influenza transmission by up to 17.3% to 40.6%; The incidence rate decreased by 5.1% to 24.8%.

Based on the relaxation of COVID-2022 public health and social measures in many countries prior to October 10 (Northern Hemisphere influenza season), the paper selected influenza virus activity surveillance data from 19 different regions and countries to model seasonal influenza prevalence in 11/2022.

The modeling results show that in the 2022/2023 influenza season, the susceptibility of the population to influenza increased by 10%~60%, which may lead to an increase of up to 1-5 times in the peak amplitude of the influenza season and an increase in epidemic size by 1-4 times.

"The short-term recovery of the epidemic scale is an inevitable process after the adjustment of the new crown prevention and control strategy, and it is also expected. However, the assessment of the epidemic during the epidemic season should not only consider the scale of the epidemic, but also the virulence of the strain itself, herd immunity and the actual burden on the medical system. In Jin Dongyan's view, this year, the 2009 H1N1 pandemic strain that caused seasonal epidemics mainly in northern hemisphere countries such as China is weakly pathogenic. From the actual situation, it has not caused a run on medical resources or a significant increase in hospitalizations.

There are also doctors from primary hospitals and tertiary public hospitals in Beijing, Shanghai, Chongqing, Hefei and other places, who recently told reporters that since mid-February, the number of patients in the hospital's fever clinic (consultation room) has indeed increased significantly, but the duration is not long (at least within a week), and few people need to be admitted to the hospital.

Jin Dongyan also said that the three-year epidemic does not mean that the immunity of healthy people is completely absent - the natural immunity formed through previous influenza infection can still play a protective role. "For different viruses, the immunity formed by the human body is persistent. It is true that the influenza vaccination rate in the mainland population is very low, but during the flu season in previous years, most people have encountered infection and self-remission until they recover, perhaps unknowingly. ”

Therefore, Jin Dongyan believes that the elderly, such as people with a heavy disease burden or abnormal immune function that affects the immune effect of influenza vaccine, can choose whether to insist on wearing masks during the influenza season from the perspective of their own protection. But for the vast majority of the population, whether they need to wear masks and maintain social distancing due to the flu "is not something that individuals should consider, but what the national disease control department needs to consider."

Why is it a "matter of the state"? Jin Dongyan explained that mild influenza does not bring major harm, and it is not necessary and not necessarily a good thing to prevent it by means such as "wearing a mask". However, if a sharp outbreak of influenza is detected in a city, which will put greater pressure on medical resources, or the transmission rate in a place is high, then it is necessary to let people wear masks, including school closures.

"Whether the country can have a more scientific 'mask strategy' depends on whether it can establish a more accurate monitoring system." In Jin Dongyan's view, there is still much room for improvement in the mainland's infectious disease surveillance system. For example, the CDC has not counted or disclosed the proportion of deaths caused by confirmed influenza among inpatients in sentinel hospitals, which makes it difficult to assess and judge the disease risk in a timely manner.

Wei Sheng, a professor at the School of Public Health and Emergency Management of Southern University of Science and Technology, also told reporters that the original intention of public health strategy formulation is to suppress the scale of the disease in a short period of time, so that the medical system does not collapse, so as to strive for a buffer period for vaccine and drug research and development. Conversely, in the seasonal influenza epidemic period, if you want to reduce NPIs, you should "lay a good foundation" and promote the vaccination of immunely vulnerable groups as soon as possible.

Is mass flu vaccination necessary?

In Jin Dongyan's view, calling on the crowd to get vaccinated against influenza is undoubtedly a good thing. But there are also beware of "good intentions doing bad things". Without significant changes in the scale of national vaccine supply, the immunization gap could widen, taking into account the financial capacity of different regions and populations. That is, the immunization rate of immune-vulnerable groups such as "one old and one young" who really need vaccination has not changed significantly.

"On the one hand, 'good steel is used on the cutting edge', the most feasible and economical way at this stage is to increase vaccine education for risk groups such as the elderly; on the other hand, more local enterprises need to be encouraged to develop more advanced vaccine technologies and launch a variety of joint vaccine products to reduce the cost and make vaccines more accessible." Jin Dongyan said.

Wei Sheng said that the low influenza vaccination rate of Chinese residents is fundamentally due to the insufficient understanding of the harm of influenza and the protective effect of influenza vaccine in the whole society.

A research article published by relevant researchers from the Central Disease Control and Infectious Disease Management Office at the end of last year said that in 2020-2021 and 2021-2022, China's total influenza vaccination rate was 3.16% and 2.47%, respectively. The WHO recommends a target for influenza vaccination rates of 75%.

As for the impact of the new crown epidemic on influenza vaccination, Wei Sheng believes that there are advantages and disadvantages. Among them, the downside is that due to the limited resources invested in vaccination work, objectively the resources invested in influenza vaccination are insufficient.

But on the bright side, medical staff have also increased people's awareness of the need for influenza vaccination when they educate about the new crown vaccination.

At a press conference of the joint prevention and control mechanism of the State Council held on November 11 last year, a set of data was released: as of November 12 of that year, the national influenza vaccine vaccination volume was about 11 million doses, which was close to the annual vaccination volume of the previous year.

Wei Sheng said that in China, influenza is still a self-funded type II vaccine, but some areas have implemented free influenza vaccination for specific groups of people, such as people over 60 years old. However, if we want to further expand the coverage of influenza vaccine, we need to raise awareness of the necessity of influenza vaccination at all levels of society, so that everyone understands that influenza vaccination is a good thing for individuals and social and economic development, so as to increase the motivation of local governments to work together among multiple departments to promote this work.

According to a study published in the Chinese Medical Journal, the national influenza-related economic burden in 2019 was 263.81 billion yuan, accounting for about 0.266% of the GDP of that year, of which the loss of productivity caused by hospitalized cases, outpatient emergency cases and premature death accounted for 86.4%, 11.3% and 2.4% of the total economic burden, respectively.

At present, it has been nearly 4 months since the peak of new crown infection, and many people choose to carry out booster immunization at this time. At this stage, this spring flu season has not yet passed, if at this time, while promoting the new crown booster vaccination work, encourage a certain proportion of people to get the flu vaccine "by the way"? Is it safe to get vaccinated at the same time?

Jin Dongyan believes that influenza vaccine and new crown and pneumococcal vaccine are safe at the same time, in addition, the elderly and patients with chronic diseases are susceptible to the above diseases, and multiple infections will also increase the possibility of the disease involving the lungs, so simultaneous vaccination, or vaccination of marketed joint vaccines are safe and feasible, worthy of promotion of vaccination.

In May 2022, WHO updated its position paper on influenza vaccines. The document believes that based on the limited evidence available, the safety and efficacy of IIV and the currently used new coronavirus vaccine have not been observed to be affected, and it is also recommended that the inactivated influenza vaccine can be administered at the same time as the new crown vaccine.

"If this spring's flu season has not passed, it is necessary to make up for this flu season at this time." Wei Sheng said. He also mentioned that the best time to vaccinate vulnerable people before the next flu season begins.

The flu vaccine is generally valid for about a year, but a vaccine for the 2023/2024 flu season is not yet available. Wei Sheng said that influenza viruses are easy to mutate, so even if you have been vaccinated with influenza vaccine, in order to improve the protective effect of the vaccine, you should also be vaccinated against the influenza strain of the season before the second half of the influenza season.

"For vulnerable groups such as the elderly, it cannot be said that because the current flu vaccine cannot be prevented next year, it will save money and not fight." Every influenza epidemic season should be vaccinated with the corresponding influenza vaccine, which is very effective in protecting vulnerable people. Wei Sheng said.