Scientists try to develop better jabs as Omicron rages around the world

To be sure, current vaccine platforms such as mRNA, adenovirus and inactivated virus prevent serious disease. But preventing infection in the least immunized and high-risk groups remains a challenge for public health officials.

The incidence of successful infections—that is, in people who have already been vaccinated—has also sparked discussion in the scientific community when it comes to mixing vaccines. “The primary metric should be looking at vaccines that prevent serious diseases. But we should also aim for vaccines that reduce overall infection or mild infection,” said Dr. Sanjay Pujari, director and chief advisor, Institute of Infectious Diseases .

Studies have shown Western countries are rushing to protect their populations with a third dose six months after vaccination. A Canadian study showed that with two doses of Pfizer and Moderna vaccines, protection against Omicron infection dropped by 50%, although this was against hospitalization and ICU stay.

Studies with the AstraZeneca vaccine in the UK showed a reduction in effectiveness against symptomatic disease for Omicron compared to Delta.

This is where the strategy for mixing dosages comes in. A large study in Denmark showed that mRNA results in better antibody titers after giving the first dose of ChAdOx (AstraZeneca). The US Food and Drug Administration authorized a mixture of Moderna’s mRNA vaccine and Johnson & Johnson’s adenovirus vaccines, because studies showed a better immune response to such a mixture.

In India, accidental mixing of Covaxin and Covishield also showed better immunity among 18 individuals in Uttar Pradesh.

In January 2022, a study by CMC Vellore on the immune responses to mixed administration of Covisheild followed by Covaxin and vice versa comparing two undiluted jabs at 56+/- 7 days intervals may shed light on the strategy.

“There is a clear need for trials exploring the safety and efficacy of heterogeneous vaccines for two reasons. First, available vaccines are targeted to specific components of the virus. Therefore, widespread action over a broad spectrum of coverage by different types of vaccines is important. Second, heterozygous vaccines pose formidable challenges to rapidly evolving viruses. The evolution of variants is readily facilitated by poor vaccination coverage. The next easy target for the virus will be monologue vaccines,” said Dr Giridhar Babu, head of Lifesciences Epidemiology, Public Health Foundation of India.

India is one of the few countries where pharma companies are working on four different vaccine platforms, which makes it ideal to conduct these experiments.