What is the novel coronavirus "breakthrough infection"? How to deal with it?

As the highly contagious variant of the COVID-19 virus, the Delta strain, has spread rapidly around the world, some countries have reported an increase in cases of "breakthrough infection" among COVID-19 vaccine recipients. What is a "breakthrough infection"? What impact will it have on the protective efficacy of the vaccine?

Cases reported in many countries

"Breakthrough infection" means that pathogens break through the vaccine's defenses, causing vaccinated people to be infected with the disease that the vaccine is supposed to prevent. Xu Ke, a professor at the State Key Laboratory of Virology at Wuhan University, said that this is because it is difficult for all vaccines to achieve 100% protection. The lower the protection, the higher the incidence of "breakthrough infection." Even for the most effective vaccines, individual differences can lead to "breakthrough infection" in individuals with lower immune responses.

Recently, some countries with high vaccination rates have reported multiple cases of "breakthrough infection". The latest statistics from the US Centers for Disease Control and Prevention show that as of July 26, the United States has reported a total of 6,587 cases of "breakthrough infection" in which patients were hospitalized or died after vaccination, of which 74% were patients aged 65 and above, and a total of 1,263 deaths.

"The elderly and those with underlying diseases are still at high risk of developing severe illness or even death after 'breakthrough infection'," said Zhang Jun, deputy director of the National Infectious Disease Diagnostic Reagents and Vaccine Engineering Technology Research Center and deputy dean of the School of Public Health of Xiamen University.

The Israeli Ministry of Health reported on July 24 that the country has found a total of 5,770 cases of "breakthrough infection" after vaccination, of which 495 are currently hospitalized and 123 have died. A study recently published in the New England Journal of Medicine showed that among 1,497 Israeli medical staff who were fully vaccinated with the Pfizer vaccine from the United States, 39 had "breakthrough infections."

Challenging vaccine effectiveness

Xu Ke pointed out that many viruses mutate quickly and escape existing vaccines, which can also cause "breakthrough infections". In the history of global vaccines, "breakthrough infections" have occurred from time to time, and the most typical example is the "breakthrough infection" incidents after influenza and hepatitis B vaccination caused by virus mutations.

The new coronavirus variants, including the Delta strain, are challenging the protective efficacy of vaccines. Zhang Jun said that "breakthrough infections" caused by the Delta strain are more common. Although it is not yet certain whether the vaccine's protective efficacy against the strain is weaker than the prototype strain, or whether the strain itself is more infectious and efficient in transmission, the neutralizing activity of serum antibodies after immunization of various vaccines currently on the market against certain strains has indeed weakened.

Data released by the Israeli Ministry of Health on July 22 showed that due to the influence of the Delta strain, the effectiveness of Pfizer's COVID-19 vaccine in preventing COVID-19 infection in Israel dropped to 39%.

However, "breakthrough infection" does not mean that the vaccine is completely ineffective. Zhang Jun said that in research reports with strong data science, the effectiveness of various vaccines in preventing death and severe illness is significantly higher than the effectiveness in preventing mild illness or infection, but "breakthrough infection" still causes severe illness and death.

How to deal with epidemic prevention

Faced with the continued mutation of the new coronavirus and the increasing number of "breakthrough infection" cases, many countries have responded by establishing a "breakthrough infection" case database and carrying out booster vaccinations.

For example, the U.S. Centers for Disease Control and Prevention has established a vaccine "breakthrough infection" database, which covers detailed information such as patient demographic information, geographic location, vaccination time, vaccine type, and infectious virus sequence. Local disease control agencies can report and query the "breakthrough infection" case information recorded in the database.

The emergence of "breakthrough infection" cases may mean that we have to accept the long-term coexistence with the new coronavirus. "We need to learn how to coexist with the virus and minimize its impact on our daily lives," said Paul Griffin, an associate professor at the University of Queensland, Australia, an expert in infectious diseases and microbiology. He believes that in response to "breakthrough infections", on the one hand, we must continue to increase vaccination coverage, and on the other hand, we should continue to maintain social distance, wear masks, and have a high detection rate.

Some experts also suggested that in order to deal with "breakthrough infections", we can accelerate the development of vaccine formulations with higher protective efficacy, appropriately increase the number of vaccine doses, that is, inject booster shots, and adopt new immune enhancement technologies.

Zhang Jun said that from the perspective of increasing the comprehensiveness of vaccine immune mobilization, the intramuscularly injected new crown vaccine currently used on a large scale mainly mobilizes systemic immune responses, but does not have the effect of local respiratory immune mobilization. Therefore, research on vaccines that can mobilize respiratory immunity and exploration of their combined use with intramuscular injection vaccines can be strengthened.

Source: Xinhua News Agency

Reporter: Peng Qian; Contributing reporters: Li Wei, Fu Min, She Yonggang

Producer: Mou Yanqiu Zhang Lihong

Editor: Dong Jingxue

Proofreading: Zhang Linglin

Internship: Zheng Yuantai