Will the Vaccine be Useful in the Future? Demystifying the Cause of the World's First 'Secondary Infection' New Coronavirus Case

The appearance of secondary infections does not affect the significance of the vaccine. Unlike natural infections of the respiratory mucosa, vaccination through intramuscular injection can be understood as a systemic infection, which will definitely form immune memory and lasting immune protection, so there is no need to worry about the persistence of immunity.

Globally, there have been reports of cases of 'Re-infected' among survivors of the new coronavirus. These cases often have no live virus in their bodies and still carry viral gene fragments, which leads to positive test results. However, on August 24, after comparing the genetic sequencing of the new coronavirus strains infected by a man twice, researchers from the Department of Microbiology at the Li Ka-shing School of Medicine at the University of Hong Kong found that the patient was infected again about 4 months after recovering from the first infection. Be infected, not 're-infected'.

Researchers say this is the world's first confirmed case of secondary infection.

The man was diagnosed with his first infection in Hong Kong on March 26. He had only mild symptoms at the time. He was hospitalized on March 29. After two tests for the virus were negative, he was discharged on April 14. On August 15, when the man traveled to Spain via the United Kingdom, he was tested at the airport and found that his saliva sample was again positive for the new coronavirus virus. He has been asymptomatic after returning to Hong Kong and admitted to the hospital. The research report was accepted by the medical journal 'Clinical Epidemiology' on August 24.

Jin Dongyan, a virology expert and professor of medicine at the University of Hong Kong, said that the previous explanation for many 're-infected' was that infected persons in the recovery period were purging infected cells in their bodies, and some virus gene fragments were detected, but The cases reported by the University of Hong Kong are exact cases of secondary infection.

Is Human Body's Immunity to the New Coronavirus Long Enough?

Previously, most scientists believed that among the coronaviruses, COVID-19 would cause a longer-lasting immune response like SARS and MERS, which is understood by ordinary people as being immune to the virus, rather than being repeatedly infected like the common cold. Stanley Perlman, a professor of microbiology and immunology at the University of Iowa in the United States, said in an interview with the media this year that they took samples from SARS patients and that antibodies could be detected until this year. He bet that the new coronavirus will not have a second infection.

Is the immune response in a person who has been infected with the new coronavirus enough to protect him from being infected again? If so, how long can this protection last? If not, is the vaccine still useful? The industry has been discussing these issues, and this case seems to give less optimistic results. 'This case proves that at least some infected people do not have long-term immunity (to the new coronavirus).' A researcher in the Hong Kong case mentioned above replied to the journal 'Science'.

However, Stanley Perlman said that from other respiratory infections, people with deep lung infections can usually avoid secondary infections. But if it is only a mild new coronavirus infection involving the upper respiratory tract, the patient may behave like a common coronavirus that causes a cold, and may be infected again.

Xu Jianqing, Director of the Institute of Emerging and Reappearing Infectious Diseases of the Shanghai Public Health Clinical Center, said that for localized infections, the immune system considers it to be a transient harm, so there is no need to form long-term memories. For the new coronavirus infection, mild patients are usually only upper respiratory mucosal infection, that is, local infection, so it is not surprising to observe that the immune response disappears within a few weeks. If you want to observe whether the immune response caused by the infection is durable, it should be carried out in severely ill patients. This type of infection is usually infected with the lung interstitium, that is, systemic infection appears.

However, the emergence of secondary infections does not affect the significance of the vaccine. Unlike natural infections of the respiratory mucosa, vaccination through intramuscular injection can be understood as a systemic infection, which will definitely form immune memory and lasting immune protection, so there is no need to worry about the persistence of immunity. A person in charge of the research and development of the new coronavirus vaccine told that natural infection and active immunity are two different things. For example, the herpes zoster virus, which has been latently infected in the human body for several years, has not produced any immune protection, but the vaccine against the virus can be cleaned after two injections.

At the same time, professionals including the World Health Organization's new coronavirus experts emphasized that the case reported by the University of Hong Kong is only an exception among the tens of millions of infected people worldwide. Moreover, the man's performance after the second infection was milder than the first, indicating that although his immune system could not completely prevent the infection, it still provided a certain degree of protection.

Jin Dongyan also believes that this case was not completely unprotected after the first infection. In fact, his second infection was completely asymptomatic. This should be attributed to the immune memory formed by the first infection that stimulated immune protection for the second time. He added that if the symptoms after re-infection are the same as the common cold, there is no need to worry. This is likely to be a scenario after the level of herd immunity increases.

Michael Mina, an immunologist at the Harvard School of Public Health, told the New York Times that there is no difference between building an immune memory and enhancing a person’s memory. The first confrontation with the new coronavirus may not produce 'complete immunity', but each exposure to the virus will cause a stronger immune response, 'usually these second and third contacts help consolidate long-term memory responses.'

'Science' magazine believes that the exact meaning of the findings of the University of Hong Kong is not clear-judging from the manuscripts obtained, the authors gave some 'general' statements, for example, herd immunity is unlikely to eliminate 'new crown epidemic', 'vaccine may not provide life-long protection against COVID-19', but such a case is difficult to draw such broad conclusions. Researchers from the University of Hong Kong said that even if the case is an exception, it also brings some hints, such as people who have recovered from the new coronavirus infection should also be vaccinated, or should continue to take preventive measures such as wearing masks and maintaining social distance.

Does Virus Mutation Affect the Effectiveness of Vaccines?

The paper also mentioned that there are 24 differences in the genetic sequence of the two infections. However, many experts believe that this amount is less than one-thousandth of the mutation of the new coronavirus with about 30,000 nucleotides, and so far, the mutation rate of the new coronavirus is very low and will not affect immunity and the effectiveness of the vaccine.

On August 17, the Deputy Minister of Health of the Philippines stated that a new coronavirus strain with the D614G mutation was found in Quezon City, where about 2.9 million people live; the previous day, the Ministry of Health of Malaysia also stated that 4 cases were found locally. Cases caused by the D614G variant strain. However, the mutation at the D614G locus did not appear recently. The mutant strain began to spread widely in Europe in early February and gradually became the world's mainstream strain. Researchers from the Scripps Research Institute in the United States have found that the mutant strain is relatively stable, and the D614G mutation is unlikely to cause the new coronavirus vaccine, antibody drugs and other treatments to be ineffective.

Earlier, according to Japan’s Yomiuri Shimbun’s report on August 8, the latest study by the National Institute of Infectious Diseases in Japan found that the March epidemic in Japan was mainly caused by the new coronavirus of European-related gene sequences. From mid-June, Tokyo as the center point, a large number of viruses with new gene sequences have appeared, and they have spread rapidly across Japan. According to a report by Xinhua News Agency on August 9, Japan’s National Institute of Infectious Diseases responded to an email saying that the above statement was wrong. In fact, only a small amount of base mutation has occurred in the new coronavirus in Japan.

Between January and February of this year, a new coronavirus mutant strain with a deletion of 382 nucleotides appeared in Singapore. This mutant type of new coronavirus has not decreased its replication ability, but its toxicity has been greatly reduced. The symptoms of infected people are even lighter and the strain has disappeared in March this year.

'The new coronavirus has mutated, causing the immune protection to fail. This is a false proposition. It has never been discovered until now.' Jin Dongyan said that although the RNA virus itself is relatively easy to mutate, this coronavirus has a corrective enzyme that makes the replication process. The chances of making mistakes in the medium are much lower.

The aforementioned vaccine scientist, who did not want to be named, said that the vaccine research and development team, including them, has done such an experiment : express the important mutations of the new coronavirus, and then use the serum after the vaccine immunization to neutralize these mutant new coronaviruses. It was found that no mutation would invalidate the immune response triggered by the vaccine, and the virus can be neutralized. 'The virus mutation is like wearing a mask, but no matter how it changes, it is still a coronavirus in general, so it can be caught by the immune system.'