COVID-19: Why Covovax and Corbrevax didn’t qualify as booster doses?

The new entrants in India’s basket of COVID-19 vaccines – Covovax and Corbevax – didn’t qualify for country’s precautionary dose program to be commenced from January 10, despite being pitched as booster shots. Extended to a certain category of beneficiaries, Indian government has only allowed to take previously administered vaccines as boosters i.e Covishield, Covaxin and Sputnik V.

Covovax is a protein subunit COVID-19 vaccine developed by Novavax Inc, an American biotechnology company based in Gaithersburg, to be manufactured and marketed in India by Serum Institute of India (SII) as covovax. Corbevax is another protein sub unit vaccine is developed by Texas Children's Hospital at the Baylor College of Medicine in Houston, Texas and dynavax technologies based in Emeryville California. It is licensed to Indian biopharmaceutical firm Biological E. Limited (BioE) for development and production.

India’s conclusion on the same vaccine as booster shot, according to the officials in health ministry, is derived from the World Health Organization's (WHO) updated playbook. The WHO issued interim recommendations for heterologous COVID-19 vaccines (different vaccines) on 16 December 2021. “Homologous (same vaccines) schedules are considered standard practice based on substantial safety, immunogenicity, and efficacy data available for each WHO emergency use listing (EUL) COVID-19 vaccine.

However, the WHO also said that depending on product availability, countries implementing WHO EUL inactivated vaccines for initial doses may consider using WHO EUL vectored or mRNA vaccines (Pfizer and Moderna) for subsequent doses, countries implementing WHO EUL vectored vaccines for initial doses may consider using WHO EUL mRNA vaccines for subsequent doses and countries implementing WHO EUL mRNA vaccines for initial doses may consider using WHO EUL vectored vaccines for subsequent doses.

A common reason for considering heterologous COVID-19 vaccine schedules is lack of availability of the same vaccine product in settings with limited or unpredictable supply, the WHO said.

Considering India’s case, of the population vaccinated 91% have received two doses of Covishield (an adenovirus vector vaccine), the AstraZeneca vaccine produced under license by Serum Institute of India and the rest have taken Covaxin (whole virion vaccine), the inactivated virus vaccine produced by Bharat Biotech.  Even though there is limited research available on performance of different vaccines as booster shots, India had limited choices.

A study done at University Hospital Southampton NHS Foundation Trust, UK, (published on line in Lancet, December 2, 2021) provides critical information to optimize selection of a ‘booster’ or ‘precautionary dose’.  

Dr Lalit Kant, Infectious Disease Epidemiologist and former head of epidemiology and communicable diseases at the Indian Council of Medical Research (ICMR) cited the results of the study and said that it tested 7 different vaccines in people who had received either two doses of AstraZeneca vaccine or two doses of Pfizer vaccine.  

“The results of AstraZeneca arm are relevant to India. The results showed that all vaccines boosted antibody and neutralizing responses. But the amount of boosting varied.  mRNA vaccine gave responses which were higher than all the other vaccines tested. Next was from a protein-based vaccine (produced by Novavax) followed by Johnson and Johnson’s vaccine, and Astra Zeneca. Last was by an inactivated vaccine (Valneva – similar to Covaxin produced in India),” mentioned Kant.

The former ICMR scientist said that mRNA vaccine (Pfizer or moderna) is still not available in India, though Genova’s mRNA vaccine may become available by February 2022. SII’s Covovax and a similar Corbevax have received emergency use authorization in only the last week of December 2021 – after the Government’s decision of precautionary dose that too is not going to be available anytime soon.

“The launch of J&J’s vaccine has been delayed in India.  “Government was left with only two options either use  Covishield and Covaxin. Since Astra Zeneca (read Covishield) produces better response than inactivated vaccine, this clinched the decision- those who received Covishield will get Covishield, and those primed with Covaxin get Covaxin,” said Kant.

Further, the WHO also warned that heterologous vaccination should only be implemented with careful consideration of current vaccine supply, vaccine supply projections, and other access considerations, alongside the potential benefits and risks of the specific products being used.

Effectiveness and duration of protection of heterologous versus homologous vaccine schedules for specific WHO EUL product combinations, especially for heterologous schedules involving inactivated vaccines given the relative lack of available data for these was also a major caution from WHO.

Dr. Praveen Gupta, Principal Director & Head, Department of Neurology, Fortis Memorial Research Institute, Gurugram argues that there is no definitive data on the concept of booster dosing in covid infection.  “Though there may be small short-term evidences and expert opinions regarding mixing of vaccines for greater immunogenicity, however, giving boosters of the same vaccine has been traditional wisdom like that for vaccines in children like DPT or tetanus or hepatitis,” said Gupta. Indicating that the government played it safe, Gupta said, “The government here has chosen the classical methodology of booster doses and advise not to change the vaccine type for booster dosing. This is a time-tested method in contrast to relatively short-term new data of mixing of vaccines.”

The government last month said that as a matter of abundant precaution, for those healthcare workers (HCWs) and Frontline workers (FLWs), all persons aged 60 years and above with comorbidities who have received two doses, if they have completed 9 months, another dose of covid-19 vaccine would be provided from 10 January 2022.  
 

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