If no new virus variants emerge after XBB, the current wave of infections may gradually subside, leaving a low-level, persistently occurring epidemic. However, if new variants continue to appear after XBB, another wave of infections may occur. Those who did not contract the virus in the first wave are at a higher risk of infection during the second wave. For reinfections, people aged 60 and older and those unvaccinated face a higher risk.

"What vaccine should we take now to prevent reinfection with COVID-19?" During the "Infection and Immunity Summit 2023," jointly hosted by the Shanghai Immunology Society and Frontiers China, Professor Dong Chen from Shanghai Jiao Tong University School of Medicine posed this question to Dr. Zhang Wenhong, director of the National Infectious Disease Medical Center (Shanghai) and head of the infectious disease department at Huashan Hospital affiliated with Fudan University.

Dr. Zhang Wenhong replied, "Hong Kong recommends administering a two-dose vaccine for this wave of the pandemic, but they say it 'can be' taken, not that it 'must be' taken. Mainland China has all types of vaccines available, but many people are considering whether waiting longer and accumulating more data on the vaccine brand might be better. Regardless, it's recommended that vulnerable groups receive a booster shot six months after their initial vaccination, either with a two-dose or a single-dose vaccine. For those under 50, Hong Kong does not have any specific recommendation, and individuals can decide for themselves. The World Health Organization is also focusing on vulnerable groups. I call on these groups to consider booster shots six months after their initial vaccination, and both two-dose and single-dose vaccines are acceptable. China's two-dose vaccines are gradually becoming available and offer slightly better protection against the Omicron variant, but this data is still only from clinical trials."

At the forum, Dr. Zhang Wenhong delivered a speech titled "Reinfections with COVID-19." He explained that data shows that if the coronavirus mutates, reinfections may slowly emerge six months later. While these reinfections are generally not widespread, a peak of infections may occur if a new variant effectively breaches the immune barriers established to combat previous variants. He stressed the importance of monitoring vulnerable populations, issuing early warnings, stockpiling medications, and quickly responding to any new variants.

COVID-19 Variations

Two waves of COVID-19 infections have appeared in various countries and regions, including Taiwan, Japan, Singapore, the United States, and the United Kingdom. Dr. Zhang Wenhong clarified that there are two primary causes for reinfections: the gradual waning of immunity in those infected during the first wave and new infections in those not infected during the first wave. According to monitoring data, many current cases in China fall into the latter category.

In response to a question from Professor Dong Chen about why the peaks of reinfections vary among different countries, Dr. Zhang Wenhong quoted U.S. infectious disease expert Dr. Fauci, saying, "The coronavirus will find every person. Once the barrier of herd immunity is established, the virus will seek out those who have not yet developed immune barriers. Therefore, countries that controlled the first wave well will have higher peaks during the second wave."

"At present, the main COVID-19 variants in China are BA.5, BF.7, and XBB. XBB accounts for 90% of the prevalent strains in the United States, 50% in Hong Kong, and its proportion in mainland China will gradually increase. It shortens the effective protection time of neutralizing antibodies, making it easier to cause reinfections," Dr. Zhang Wenhong said. He emphasized the importance of understanding the characteristics of these new variants and how they impact the existing immunity within populations.

Dr. Zhang Wenhong also discussed strategies to manage the risk of reinfection. He said that the development of better, more effective vaccines is crucial. Additionally, countries should invest in research to understand the relationship between emerging variants and the waning immunity in the population. This knowledge can help inform public health policies, vaccination strategies, and guide the development of new therapies.

He also highlighted the importance of global cooperation in combating the pandemic. "The COVID-19 pandemic is a global issue, and only through international collaboration can we effectively deal with it. We must share resources, knowledge, and technology to help each other and eradicate the virus as soon as possible," Dr. Zhang Wenhong said.

Finally, he encouraged individuals to continue practicing good hygiene, maintaining social distance when necessary, and staying informed about the latest COVID-19 developments. As the situation evolves, it is crucial for people to stay vigilant and follow guidelines provided by public health officials.

While the threat of reinfection looms, experts like Dr. Zhang Wenhong are working tirelessly to better understand the virus, its variants, and the best strategies to protect populations. As new information emerges, it is essential for individuals to stay informed and make decisions based on the latest guidance from public health officials. For vulnerable groups, considering a booster shot six months after their initial vaccination is recommended, while individuals under 50 can decide for themselves whether to receive a booster or not.