Precautionary dose of COVID vaccine: Lancet study finds mix-and-match booster more effective than more-of-same

In study on booster vaccines, the researchers saw only three serious adverse events related to the vaccine. All recovered completely. (Representational image)

Mixing COVID-19 vaccines for the booster dose was shown to be more effective than administering more of the same vaccine for the third shot, according to a study recently published in the Lancet.

The Phase-IV study also showed that heterologous boosting (by mixing vaccines) increased protection against both delta and omicron variants. 

This finding is particularly relevant for India, which has decided not to mix vaccines for the booster/precautionary dose.

Read also: Coronavirus Omicron India LIVE

The study was led by Prof. Dr. Sue Ann Clemens, who is the director of Vaccine Group Oxford Brazil and who was awarded honorary CBE last September for her contribution to public health. It had 1,240 participants from Brazil, of 18 years and above, and was funded by the Ministry of Health, Brazil.  

The mRNA advantage

The researchers had found that CoronaVac or Sinovac, which is a dose of dead viruses, had been used widely for the first two doses. So they tested the booster-dose administration against that–giving CoronaVac as the third dose for homologous (or same-shot) testing; and giving an MRNA and two  vector-vaccines for the heterologous (mix-and-match) testing. 

The highest antibody concentrations were seen after an mRNA (Pfizer-BioNTech) boost.

India is yet to give approval to the Pfizer-BioNTech vaccine because the company has been asking for overseas indemnity, which will protect Pfizer from paying damages in case of adverse reactions. 

India’s National Technical Advisory Group on Immunisation, or NTAGI, had advised against mixing vaccines for the precautionary dose. They had said that mixing results in increased reactogenicity, which is a measure of adverse reactions from vaccination.

One of the members had told The Economic Times in an interview that the advisory group is open to modification if evidence suggests that benefits outweigh risks. 

Read also: How safe and effective is the mix-and-match third dose?

In the study, only five serious adverse events were recorded. In that, only three were considered vaccine-related–in the BNT162b2 (Pfizer-BioNTech) group, a woman of 83 years had a pulmonary embolism and deep vein thrombosis two days after vaccination; and in the Ad26. COV2-S (Janssen) group, a woman of 52 years had a subconjunctival haemorrhage two days after vaccination, and a man of 71 years had a pulmonary embolism 28 days after vaccination.

All five recovered.

A commentary on the study, which was also published in Lancet, said, “This safety profile is reassuring and will likely not influence the choice of booster vaccine in clinical practice.”

For better booster coverage

Dr Vishal Rao, the regional director of Head Neck Surgical Oncology and robotic surgery, and Associate Dean for Centre of Academic Research at HealthCare Global (HCG) Cancer centre in Bengaluru, had said that mixing of vaccines can improve booster-dose coverage in India. 

In an opinion piece he wrote for Moneycontrol, he had said, “One thing that impedes India’s booster drive is the country’s policy of only allowing booster/precautionary doses that are the same as their earlier doses. Unlike other nations, India hasn’t approved the mixing of vaccines. This approach has ‘very modest’ advantages in most situations.”

He said mixing was a better option. 

For one, production of the two major vaccines in India–Covishield and Covaxin–is still limited when compared to what the country needs. For another, studies by reputed global health organisations such as the US Centers for Disease Control and Prevention and UK’s NHS had given the go-ahead for mix-and-match administration after studying its reactogenicity (adverse reactions) and immunogenicity (effectiveness).