Aerosolized inhalable COVID-19 vaccine developed by CanSinoBIO is on display at the Fifth Hainan International Health Industry Expo on November 12, 2021. Photo: VCG

A latest research shows that heterologous booster with inhaled adenovirus vector vaccine can generate more neutralizing antibodies against different COVID-19 variants, which is expected to be an effective strategy in preventing the spread of Omicron variant BA.5, one of the major variants that have caused the recent flare-ups in China.

The rapid widespread Omicron subvariant BA.5 of COVID-19 has become a potential imminent pandemic threat, but available vaccines lack high efficacy against this subvariant.

The Joint Prevention and Control Mechanism of the State Council announced recently that the BA.5 variant is one of the major variants that caused the latest flare-ups in China.

The research, published on October 5 in the Emerging Microbes & Infections, a well-known infectious diseases journal, shows that the aerosol inhalation of adenoviral vector COVID-19 vaccine after two doses of inactivated vaccine leads to higher levels of neutralizing antibodies against a variety of variants including BA.5.

Aerosolized immunization of the vaccine can induce local mucosal IgA antibodies at the respiratory mucosa and induce higher level of antibody count against the Omicron variants in blood, which may effectively control the Omicron variant BA.5.

To assess whether heterologous immunization with aerosol inhalation induces robust antibody immune response, 150 participants who had received one booster dose 6 months after two doses of inactivated vaccine were selected and divided into three groups to test three vaccination strategies.

The research shows that the third dose of aerosol inhalation of adenovirus vector vaccine induces superior anti-spike antibody response to intramuscular inactivated vaccination, with higher levels of antibodies induced against either original viral strains or Omicron variants.

Compared with intramuscular inactivated vaccine following two doses of intramuscular inactivated vaccines, heterologous booster with inhaled adenovirus vector vaccine can induce higher levels of antibodies against multiple Omicron variants, according to the research.

The research also found that for all the COVID-19 strains that were covered in the study, the inhalation group had a significant advantage in inducing neutralizing antibody responses.

Inhalable vaccines based on adenovirus type 5 vector (Ad5) were designed to imitate the manner in which SARS-CoV-2 enters human bodies via the airways. Thus, it can induce a localized immune response targeting the mucosal surfaces to which pathogens attach instead of inducing a systematic immune response, which is facilitated by intramuscular vaccines.

The research findings strengthen recent evidence that targeted mucosal immunization may be an effective strategy for controlling the expecting spike in BA.5-induced infections in the COVID-19 pandemic based on two inactivated vaccines.

New subvariants of Omicron BA.5 including BA.5.1.7 and BF.7 have been discovered in multiple places across China including South China's Guangdong Province, North China's Inner Mongolia Autonomous Region and East China's Shandong Province over the past few days. Both of the new subvariants are highly infectious with fast spreading speed. Experts have warned that if decisive prevention measures were not adopted in time, there is high possibility that they could become the dominant variants in China.

Global Times