Spike in Hospitalisation, Deaths Unlikely With Omicron Variants: K Srinath Reddy

In the fourth year of the ongoing pandemic, the Omicron variants of the SARS-CoV-2 virus, which causes the COVID-19 disease, is still throwing challenges before shaky healthcare systems around the world. Rashme Sehgal speaks with Dr K Srinath Reddy, distinguished professor with the Public Health Foundation of India, to discuss the challenges, and whether the vaccines we have can still prevent serious illness in those who catch the infection. Edited excerpts:

RS: What is the sub-unit protein vaccine and is it a breakthrough in vaccine technology to be used to combat COVID-19? Can you talk about the development of Covovax and Corbevax, the subunit vaccines?

KSR: Subunit protein vaccines have emerged later in this battle against COVID-19, though the platform has been familiar for several years. For example, the vaccines against Hepatitis B and E are of this type. In COVID-19, the mRNA vaccines are the novel ones. They, along with virus vector vaccines, have been extensively employed in the current pandemic.

Corbevax is being produced through a partnership between Biological E., a Hyderabad-based vaccine manufacturer and Houston-based scientists affiliated to the Baylor College of Medicine in the United States of America. Covovax is being produced by the Serum Institute of India, as the Indian version of a vaccine developed in the United States by Novavax company. Both these vaccines emerged in 2021.

RS: How extensively have these sub-unit vaccines been tested, how do they work and what is the situation regarding their side effects?

KSR: Novavax vaccine underwent placebo controlled clinical trials in the United States and was reported to show 90% efficacy in adults and 80% efficacy in adolescents against the earlier versions of the SARS-CoV-2 virus. This was against symptomatic Covid-19. Corbevax undertook immunological response studies to demonstrate the effect of evoked neutralising antibodies against the Wuhan, Delta and Beta strains of the virus. Based on these, an efficacy of 90% was reported.

Sub-unit protein vaccines do not present the full virus to the human body. Unlike mRNA vaccines, they do not use the genetic machinery of the body to produce the spike protein. They do not use a carrier virus to deliver the spike protein, unlike virus vector vaccines. Therefore, they are far less likely to evoke adverse reactions. mRNA vaccines have been associated with some cases of myocarditis (inflammation of heart muscle), especially among males who received those vaccines. Virus vector vaccines have been associated with the complication of thrombosis (blood clot formation) in veins and arteries. Sub-unit protein vaccines are not associated with either type of adverse effects.

RS: What is the status of Corbevax and Covovax vis-a-vis World Health Organisation (WHO) approval?

KSR: Novavax has received WHO approval. That is applicable to Covavax. Corbevax is awaiting WHO approval after data submission. Since the vaccine trial used immunological correlates of protection to assess vaccine efficacy, rather than disease related outcomes, the criteria for evaluation of efficacy will be different.

RS: Are these vaccines safe for children?

KSR: Sub-unit protein vaccines are considered safe for children, based on the past record of safety of that platform. Studies done in India, too, have not reported worrisome adverse effects.

RS: Should those who have already taken booster shots be ready to take a sub-unit protein vaccine?

KSR: It is not essential for persons who have taken three doses of the vaccine to take a fourth dose. Especially if they have also acquired ‘hybrid immunity’, through natural infection and a full course of vaccines. However, an immunity booster may be needed in immunocompromised or very elderly persons whose immunity levels are fading because of several months lapsing since their last vaccination.

RS: Cases of COVID-19 are spiking in Karnataka and Kerala. Are we going to see similar spikes across the country?

KSR: The recent Omicron variants are highly transmissible. If people move around the country, the virus will travel with them. Infections may rise. However, given the background of widespread hybrid immunity in the population, the likelihood of a spate of serious infections, hospitalisation and deaths is low, unless Omicron yields place to a more virulent variant.

RS: China has witnessed a sharp rise in Covid-19 cases and some Western epidemiologists say deaths could cross two million. Is the situation there this grim?

KSR: The estimates from Western modellers may not hold true. The current wave is being caused by Omicron, not Delta. The Chinese vaccines have conferred some level of immunity. The most vulnerable are the elderly, an under-vaccinated group. Efforts are underway to vaccinate them. While China will undoubtedly see many cases of infection, the deaths are unlikely to reach the humongous numbers being forecast by Western media. The experience of small, tightly-packed Hong Kong cannot be extrapolated to all of China, which is much larger and more differentiated across its provinces.

RS: Is the perception that Chinese vaccines are not-so-effective correct?

KSR: When the Covid-19 disease came in through a novel virus, there was no prior experience of how effective vaccines against it would be. So, the bar was set at 50% efficacy in preventing clinically manifest Covid-19 disease, in placebo-controlled trials. Chinese vaccines which crossed that mark gained approval. Other vaccines showed higher efficacy rates over 80% or 90%.