Why China Lacks Hybrid Immunity: Epidemiologist Explains

Expert explained that how this immunity is a combination of natural infection and vaccination and is immunologically superior to infection-induced or vaccine-induced immunity alone

According to the WHO, herd immunity stands for population immunity and it provides the indirect protection from an infectious disease that happens when a population is immune either through vaccination or develops immunity through previous infections. While the efficacy of this immunity against severe infection and death is still debatable, experts believe that it has globally contributed in the development of a strong immune response against the virus.

Today China is facing a grim situation with millions of lives at stake and at risk of dying from serious illness inflicted by the COVID virus. Among the many speculations around the surging cases is one that holds the sudden reversal of Zero-COVID policy as accountable for the situation. While pulling down the stringent measures might seem optimistic, it might have done more harm than good to a population who lacks a community immune response against the infection.

Why Chinese might be lacking herd immunity? Epidemiologist explains

There is growing evidence that hybrid immunity that is provided by a combination of infection and vaccination drive. It provides better protection against subsequent COVID-19 strains, better than vaccination or infection alone. Many of you would be thinking that how it might be related to the Zero-COVID policy. China exercised some of the toughest measures in the fight against COVID-19. The policy included stringent rules like implantation of lockdown up till there was not a single active case to be found.

Dr Rohit Kumar Garg, Consultant, Department of Infectious Diseases (Amrita Hospital, Faridabad) explained how the sudden reversal of the stringent measures backfired in terms of developing herd or hybrid immunity.

He said: "The current surge in COVID cases is possibly a combined result of lifting COVID restrictions in the background of several factors. A large proportion of the Chinese population has remained underexposed to natural infection, resulting in inadequate hybrid immunity. There has been complete reliance on domestic vaccines, which are considered inferior in efficacy as compared to modern techniques based vaccines such as mRNA vaccines, which were rejected in China. Also, the lack of administration of booster doses due to vaccine hesitancy has contributed to lowered protection."

Dr Garg explained that the lack of exposure to naturally occurring strains has made the people there more vulnerable to several other variants. The lifting of restrictions have resulted in large number of patients, with inadequate cross-protection against non-vaccine strains (and viral antigens), getting infected and developing symptomatic infection.

Role of hybrid immunity in fight against COVID

Talking about the ways in which excessively stringent preventive measures hamper hybrid immunity, Dr Garg explained that how this immunity is a combination of natural infection and vaccination and is immunologically superior to infection-induced or vaccine-induced immunity alone. He said that when a population does not get exposed to naturally infecting strains, it might naturally impair the hybrid immunity. In addition if the vaccination drive is not enthusiastic, the outcome is even poorer.

The expert said: "Studies have shown that hybrid immunity provides a modest benefit over infection-induced immunity or vaccine-induced immunity against infection and symptomatic infection. The benefit is due to broad immune response as a result of exposure to diverse groups of strains (and viral antigens). However, whether hybrid immunity will persist and protect against newer variants and how long, is yet to be seen."

Dr Garg also cautioned against the misinterpretation that the concept of hybrid immunity might become prone to. He informed that in no way hybrid immunity is to encourage the population to deliberately acquire the infection.

Should it be a concern for the world?

Responding to the tense situation in China and how it might be a concern for other countries, Dr Garg said: "The available data does not indicate any one variant to be a predominant cause for this outbreak. However, the detection of Omicron sub-variants BF.7 and BA.5.1.7, is worrisome. These variants are believed to be highly contagious and potentially immune evasive, even in patients with natural or infection induced immunity. Furthermore, there is a possibility of an emergence of newer mutant strains. The situation currently is not alarming for the rest of the world, however, it raises a cause for concern and underscores the importance of continuing social vaccination measures i.e.,, use of masks, social distancing etc., while preparing to be geared up, should there be a surge of cases in India or elsewhere.