A large vaccine is needed to protect against future COVID-19 relapses

The first long-term seroprevalence study of residents in Wuhan, China, found that 6.9% of people in the city had antibodies against COVID-19 in April 2020, and had asymptomatic disease. 82% of those people.

In addition, 40% of people with antibodies developed neutral antibodies, and these levels did not decrease between April and October-December 2020. The results are published in a observational study of 9,542 people in the Lancet.

The authors say that understanding seroprevalence and how antibody levels change over time in Wuhan will help inform their vaccination strategy, with their findings highlighting the need for major vaccine to protect against future virus reactivation.

The latest seroprevalence study from Wuhan builds on previous seroprevalence studies conducted worldwide, including in Geneva (Switzerland), Spain, the USA, Iceland and the Netherlands. , which has tried to shed light on the true extent of diseases in populations. This is especially important as asymptomatic disease rates are uncertain, with estimates ranging from 6% to 96% worldwide.

Assessing the proportion of the population that has been infected with SARS-CoV-2 and which is immune is critical for determining effective prevention and control strategies to reduces the likelihood of the disease spreading in the future. Because people with mild illnesses may not seek medical care and asymptomatic people are not usually screened, there may be significant differences between the reported cases of COVID-19, and actual cases of infection, proven by experiences and data from other countries. . “

Dr. Chen Wang, Principal study author, Chinese Academy of Medical Sciences & Peking Union Medical College, China

He continues: “Even in the midst of the pandemic in China, with more than 50,000 confirmed cases as of April 8, 2020, estimated seroprevalence in Wuhan remains low, with around 40% of people developing antibodies neutral antibodies, suggesting that there is still a lack of immunity in the population. “

Study participants lived across the 13 districts in Wuhan, with all family members invited to participate. All ages were included in the study, but people with serious illnesses (such as advanced cancer or severe mental illness) were excluded.

Participants completed a questionnaire of demographic and health information, including whether they had previously been diagnosed with COVID-19 or if they had COVID-19 symptoms from 1 December 2019.

Blood samples were taken for testing for the presence of antibodies in mid-April 2020, mid-June, and between October and December. Infections were classified as symptomatic if a participant reported having fever and / or respiratory symptoms and was positive for COVID-19 antibodies. The study included 9,542 people from 3,556 households.

Of the 9,542 participants, 532 had antibodies against COVID-19. When adjusted, this equated to a seroprevalence of 6.9% in the Wuhan population.

The authors found that women had higher seroprevalence than men, people aged 66 years or older with the highest seroprevalence than any other age group, health care workers had higher seroprevalence than other occupations, and people who had visited a hospital in the past five months had higher seroprevalence than those who had not.

437 (82%) of 532 participants were positive for asymptomatic antibodies. The authors of the study note that this is much higher than previous estimates of 40-45% reported worldwide.

They say this may be due to memory bias where participants reported their own symptoms five months later, but they also say this does not seem to be over-appreciated. on frequency largely in their study because strict measures were taken in Wuhan to identify all cases, and Wuhan residents were vigilant in recording their symptoms at the time of the uprising. .

Approximately 40% of participants (212/532 individuals) were positive for neutralizing antibodies – those that protect against future infections – in April 2020. The proportion of people at whether neutral antibodies remained stable for both follow-up periods – by 45% (162/363 people) in June 2020, and 41% (187/454 people) in October-December 2020.

In addition, looking at the levels of neutralization of antibodies in human blood using data from 335 people who attended the three blood tests, the authors found that the these levels significantly over the nine months of the study. However, people who had asymptomatic COVID-19 had lower levels than people who had received confirmed or symptomatic COVID-19 infection.

The co-author, Dr. Lili Ren, Institute of Pathogen Biology, Chinese Academy of Medical Sciences & Peking Union Medical College, China, says: “Little is known about the sustainability of protective responses against SARS-CoV-2 over In our study, we found that the proportion of participants with antibodies against SARS-CoV-2 was maintained for at least nine months.Importantly, we found that the neutralization of antibody titers stay stable for at least nine months. “

The authors note some limitations in their study, including not being able to determine when participants were infected and taking antibodies because the majority of some cases are asymptomatic and not confirmed by PCR test at the onset of the disease. However, they note that very few cases of COVID-19 were reported in Wuhan between mid-March and April 2020, so it is assumed that co-infection occurred. at least 4 weeks before blood samples were taken.

Linked Opinion authors, Professor Richard Strugnell and Dr Nancy Wang (not involved in the study) from the Doherty Institute, Australia, say the seroprevalence estimate suggests that the number of diseases in Wuhan is likely to exceed the number of COVID-19s reported. cases in Wuhan.

They write: “If the level of seroconversion is a true reflection of exposure to SARS-CoV-2, the apparent difference between low case numbers and high levels of seroconversion seems to suggest that most individuals antibodies to SARS-CoV-2 after asymptomatic infection. . “

They also note that the findings have provided a much deeper understanding of natural seroconversion in a major city in the pandemic, and that the findings confirm their success. in controlling the Wuhan revolution of COVID-19 at a time of testing, detection and handling facilities. much less improvement:

“Effective global administration of COVID-19 may succeed or fail depending on the immunity caused by natural infections and, in particular, vaccines. Given the rarity of neutralizing antibodies through natural diseases, the study by He and his colleagues confirms the need for effective COVID-19 vaccines in population control of the disease.

The remarkable, rapid and effective control measures implemented in Wuhan may have not only limited the spread of the virus, but also reduced the immunity of naturally occurring herds by eliminating the development of neutral antibodies. neutral. “

While other national and local governments have used other and generally less effective strategies to control the spread of COVID-19, even in highly endemic communities the incidence of disease is generally too low. to protect the herd enough to protect the population.

“The findings of himself and his colleagues suggest that herd immunity does not improve after natural transmission in situations where infection control methods have been successfully introduced, reinforcing the importance of pre- effective vaccination mechanisms to control the spread of COVID-19. This study is an important milestone in the description of SARS-CoV-2 infection and our understanding of immunity in the pandemic. “