Sohu Medicine | Dr. Fauci: Do you want to redefine the herd immunity of the new coronavirus?

Producer | Sohu Health

Author | Zhou Yichuan

Editor | Yuan Yue

< p data-track="4">At the beginning of 2021, the launch of two new crown vaccines in the United States injected a booster to the response to the epidemic. It is believed that relying on vaccines can achieve herd immunity and defeat the virus. To this day, the virus is still not under control in the United States, what is the problem?

CNN website issued an article introducing that for a period of time after the vaccine is launched, Americans will pin their hopes on herd immunity, and the focus of experts and society is the number and proportion of vaccinations , not a diagnosis, hospitalization, or death. They believe that when the number of vaccinations reaches a certain level, the population will truly achieve herd immunity. Even if someone is infected, the vast majority of people he comes into contact with are immune to being infected, and the virus will have nowhere to go. Even minors who have not been vaccinated or people with poor immune responses can be protected by a safety net because of the immunity of the surrounding population.

Unfortunately, the United States has been the country most affected by the epidemic.

Recently, Dr. Fauci, director of the National Institute of Allergy and Infectious Diseases and a renowned infectious disease expert, published a paper on herd immunity in the Journal of Infectious Diseases. In an interview, he pointed out that the United States has achieved herd immunity in the fight against rubella and measles, but this concept of classic herd immunity is not applicable to the new coronavirus. For a long time, the American population will not be free from the presence of the new coronavirus.

Fauci recalls that measles prevention and control is an ideal case study of herd immunity. Measles is an airborne virus that is so contagious that if everyone is not vaccinated, an infected person can infect 90% of their contacts. The current Omicron may have reached this level of transmission.

The achievement of herd immunity against the measles virus in the United States stems from three factors: a very effective vaccine, the virus does not mutate, and an effective push to vaccinate children. According to CDC data in the United States, the prevention rate of measles vaccine is 97%, and a single vaccination can provide life-long immunity; many states in the United States have set children’s vaccination goals, requiring more than 90% of children in kindergartens to be vaccinated. Extensive and long-term vaccine coverage has allowed the United States to successfully prevent a large outbreak of the virus. Of course, the U.S. also sees a certain number of cases each year, and it’s possible that travelers brought the virus into the U.S. But with widespread community immunization, the measles virus did not gain a foothold and continue to spread.

It is undeniable that immunity to measles has weakened in the United States and many parts of the world in recent years due to the influence of anti-vaccine groups. In 2019, the World Health Organization warned that as vaccination rates for measles decline, a worldwide epidemic is likely.

However, these rules do not apply to COVID-19. First, the new coronavirus has undergone a large number of mutations, including Alpha, Beta, Delta, Omicron, and now the Omicron variant BA.2, and BA.2 has become the reason for the rise in the number of cases in the United States in recent weeks.

The second point is that safe and effective COVID-19 vaccines are not widely accepted, and the vaccination rate is still substandard, and the vaccination rate in the United States has never exceeded 70%. Dr Adam Kucharski, co-director of the Centre for Epidemic Preparedness and Response at the London School of Hygiene and Tropical Medicine, said that the more contagious the virus, the greater the need for vaccination to prevent community transmission, which was initially set at 70 per cent and can now only be higher. In the case of Delta, if the vaccine provides 85% protection against a confirmed diagnosis, 98% of the population is required to be vaccinated. If the vaccine’s effectiveness against the virus does not meet this standard, then herd immunity will not be achieved.

Third, the realization of herd immunity depends on the prevention of virus transmission by vaccines, that is, bactericidal immunity. The measles vaccine can completely avoid infecting others, but the new crown vaccine cannot, and there are cases of transmission even after vaccination.

In short, if the vast majority of people cannot be vaccinated, and the vaccine does not stop the spread of this highly contagious and constantly mutating virus that affects the entire population, The goal of herd immunity will not be achieved. Also, vaccines and natural immunity after infection are not lifelong, which means that we can only maintain our immunity to the virus through repeated vaccinations or infections.

Encouragingly, after more than two years of virus transmission and more than a year of vaccines and booster vaccinations, the United States already has a certain degree of population immunity, as well as Widely available diagnostic tests, including antiviral drugs and monoclonal antibody treatments, have the potential to control community transmission of the outbreak without disrupting the functioning of society. Classic herd immunity no longer applies, and the latest herd immunity goal is to keep Covid-19 under control.

Going forward, we will develop a vaccine with broad protection against more variants, resulting in longer-lasting immunity, coupled with the classic non-drug public Hygiene measures are used to control the epidemic under a certain number and eventually return to normal.



Is herd immunity for Covid-19 still possible? html

2. The Journal of Infectious Diseases

The Concept of Classical Herd Immunity May Not Apply to COVID-19< /p>