Recently, after the emergence of “new Coronavirus secondary infections” in Hong Kong, there have also been “secondary infections” in Europe. Does it mean that the antibody disappears faster than expected? Does it have an impact on vaccine development? How do the experts interpret this phenomenon?
1 Reinfection Found in Chinease Hong Kong, Netherlands, Belgium and USA
The Dutch national broadcaster NOS quoted a virologist as saying on the 25th local time that one patient in the Netherlands and Belgium each had been confirmed to be infected with the new crown virus for the second time.
The Dutch patient is an elderly person with a weakened immune system. Virologists emphasized that to determine whether it is the second infection of the new coronavirus, it is necessary to conduct a viral genetic test on the first and second infections to find out whether the two viruses are slightly different.
Belgian patients currently have mild symptoms, but “this is not good news” because it shows that the antibodies produced by the patient during the first infection are not enough to prevent the second infection with a slightly different variant of the new coronavirus.
Virologists said that it is not yet clear whether this condition is rare, or “more people may be infected with the new coronavirus again after six or seven months of recovery.”
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Researchers from the University of Nevada and the Nevada Public Health Laboratory jointly released a research report on a preprinted website, showing that the man lived in Nevada and had mild symptoms such as a sore throat and cough at the end of March. He was tested for the new coronavirus in April. The result was positive, and he subsequently recovered and tested negative for two new coronaviruses. He developed fever, cough and other symptoms at the end of May and sought medical treatment. At the beginning of June, he tested positive for the new coronavirus and was in a serious condition. He needed to be hospitalized for treatment such as oxygen inhalation.
2 Asymptomatic and contagious, but highly contagious time is shortened
According to The Paper, Jin Dongyan, professor of precision medicine at the Huo Guangwen Foundation of the University of Hong Kong, said in an exclusive interview with The Paper that the patient’s second infection has two obvious characteristics. One is that it is asymptomatic but still infectious, and the other is The contagion window has been shortened.
The research team said that after the patient’s second infection, the virus mainly appeared in the nasal cavity, and almost no virus was detected in the lungs and respiratory tract. “Because our main way to prevent viral infections in our nasal cavity is mucosal immunity, and the mucosal immune memory produced by the new coronavirus infection is weak, so during the second infection, a relatively high concentration of new coronavirus will be replicated in the nasal cavity.” Jin Dongyan added.
3 Why does “secondary infection” happen?
Wu Zunyou, chief epidemiologist at the Chinese Center for Disease Control and Prevention, analyzed that humans will produce antibodies after being infected with the virus, but not all the protective effects of antibodies produced by infectious diseases are lifelong, and antibodies will gradually decrease.
Although the case discovered this time has a variation in the genetic sequence of the virus strain, it is not an infection caused by the same strain, but at present, it is more likely that the human body’s immune protection effect is not so long, resulting in a “secondary infection”.
4 Where did the antibody go?
Wu Zunyou said that the academic community has been aware of this phenomenon for a long time. For viruses such as coronaviruses, the time for the antibodies produced after human infection to achieve the protective effect is only about 6 to 12 months.
An important judgment brought by the case discovered this time is that the antibody itself will decay, and the decay speed may be faster than expected.
However, the disappearance of antibodies does not mean that the protection is completely lost. Li Bin, chairman of the Science Work Committee of the Chinese Society of Cell Biology, said that the human body will produce humoral and cellular immunity against new coronavirus infections. After the infection subsides, there are often memory T cells against the virus that survive in the human body and produce T cell immunity.
For example, this patient in Hong Kong was re-infected with a milder condition than the previous one, indicating that his immune system provided some degree of protection, even if it could not completely prevent the infection.
5 Is the vaccine still protective?
The emergence of “secondary infections” also raises another concern: Will the vaccine being developed lose its protective effect?
Yuan Guoyong, academician of the Chinese Academy of Engineering and chair professor of the Department of Microbiology at the Li Ka-shing School of Medicine of the University of Hong Kong, said that in fact, the patient in Hong Kong quickly developed antibodies and reduced the viral load during the second infection. He believes that the two-dose vaccination method will be the correct way to obtain reliable immunity.
However, he also said that how long the immune response after natural infection or vaccination is is still to be further studied. In addition, patients with mild COVID-19 may still need to be vaccinated to recover. This part of the group still needs to wear masks, observe hand hygiene and maintain social distance.
Some experts believe that even if the vaccine needs to be updated, it is not difficult to achieve technically, so there is no need to panic too much. Moreover, based on current understanding, the mutation of the new coronavirus is not as fast as the influenza virus.
Li Bin analyzed that there are at least five different strategies for vaccine development. Each strategy, even for some subunit protein vaccines, uses sequences of conserved regions of the virus, especially for the S protein bound to the ACE2 receptor on the host cell surface.
“No matter how the virus mutates, it always has to enter the cell to infect. To infect the cell, it must bind to the ACE2 receptor. Most vaccine development strategies are designed to prevent this combination.”
What’s more, becoming reinfected does not mean the virus will necessarily be transmitted — it depends on the viral dose and the susceptibility of people around the infected person.
If they are all immunised with a vaccine, we generate a ring of fire that can contain spread of the virus.
It’s also possible Sars-CoV-2 becomes an endemic virus, like many viruses circulating in the population.
But as long as there are diagnostics, vaccines and treatments, we could continue functioning normally just as we do with influenza present in the population.
Ultimately it’s about what level of risk society is willing to accept. And we may need to use infection control methods like masks and hand hygiene for some time.