How long will the COVID-19 Last vaccine? Will the immune response be strong in anyone who receives it? These questions are frequently asked as vaccines are about to be introduced in India. The responses, be it six months or two years, assume that the strength and duration of the vaccine response will depend entirely on the vaccine, regardless of the age, nutritional status, or pre-existing health of the person receiving the vaccine.

Ignoring diet as a major determinant of both natural or innate immunity and acquired or adaptive immunity developed in response to infection or a vaccine has consequences. It usually does not affect the decision to immunize, but ignoring this aspect leads to a neglect of diet in both public health policy and clinical practice.

A vaccine just provides the antigenic stimulus for the body to respond. How well the body reacts depends largely on the nutritional status and varies from person to person. Different facets of diet influence this response. The diet may lack important nutrients needed for a robust immune response. It may contain elements that cause high levels of inflammation in the body and deplete the building blocks of immunity that could be better used for the adaptive response to the vaccine. These effects are very likely when the diet is high in ultra-processed foods. Diet can also affect the composition of our gut microbiome, which, with its trillions of bacteria, turns out to be an important factor influencing our immunity. The healthy microbiome thrives on plant-based soluble fiber in food and is destabilized by excessive sugar, trans fats, red and processed meat, alcohol and tobacco.

Studies of the immune response to various vaccines, from polio and cholera to rotavirus, have shown that a deficiency in several important nutrients adversely affects the strength of the immune response. Dietary protein deficiency is an obvious culprit, as antibodies are proteins too. Zinc and selenium are important minerals that have been shown to potentiate the effectiveness of the vaccine, aside from improving natural (innate) immunity. Vitamin E has also been suggested as a nutrient that boosts the immune response to a vaccine.

It is not just the antibody levels that are affected by diet. The more permanent component of the body’s immune response, cellular immunity, is affected by diet. In 2006, Japanese researchers reported that mice fed 5 percent casein (milk protein) had lower T cell counts than mice fed 20 percent milk protein. The production of interleukin-2, an important component of chemical ammunition in the body’s response, was lower among CD4 + T cells in the low protein diet group. The researchers concluded that “in addition to developing an effective DNA vaccine, nutritional management is important for the prevention of infectious diseases through DNA vaccination.”

A double-blind, placebo-controlled clinical study in France found that elderly people in a nursing home developed more antibodies and fewer respiratory infections compared to a similar group who did not receive zinc and selenium supplements. The immune system needs these two minerals for a strong response against viral infections. This applies to both natural immunity and the immune response to a given vaccine.

It is not necessary to supplement these nutrients along with the administration of the vaccine. This would not be possible in a mass immunization program, although nutritional counseling can be provided along with vaccination during the post-injection observation period. What is needed is a review of the policies that influence our agricultural priorities and shape our food systems. Enabling people to eat healthily will help boost natural immunity, fight off microbial infections, and build a robust immune response when stimulated by a vaccine.

Are our agriculture and food systems currently configured for this? Unfortunately not. Currently, we offer fiber-free grains and ultra-processed foods without adequate and affordable supplies of legumes, millet, fruits, vegetables, nuts, and fish that can provide us with much-needed proteins, vitamins, minerals, and fiber. Some states are even removing eggs from school lunch menus despite being full of the nutrients needed for immunity.

The effects of climate change also need to be considered when examining the future of food systems and nutrition in our country. A study by Columbia University (Data Science Institute, 2018) estimates the impact of climate change on India by 2050. The nutrient quality of staple foods would decrease, according to the study. It is estimated that global warming would result in 49.6 million new zinc-deficient people, 38.2 million new protein-deficient people, apart from 106.1 million children and 396 million iron-deficient women. It concludes that diversifying crop production, replacing some of the rice cultivation with millet and sorghum, would make India’s food supply more nutritious while reducing irrigation needs, energy use and greenhouse gas emissions. “Such diversification of crops would also improve India’s climate resilience without reducing calorie production or requiring more land,” the study concludes.

Even as we prepare to immunize our many millions, the major public health challenge of nutrition remains the production of readily available and affordable food sources that enable people to maintain a balanced diet over a long life cycle that is physiologically suitable for growth and good health. These diets should also be predominantly plant-based so that they are both nutritionally appropriate and environmentally sustainable. Ultra-processed foods should be regulated and taxed to reduce their production, promotion and consumption. These steps are not only good for human nutrition, but also for reducing the risk of zoonotic infections by maintaining an ecological balance. The bonus is an advantage in slowing climate change. Our protection lies not just at the tip of a needle that injects the vaccine, but most importantly in the guidelines that determine what fills our plates as we eat.

This article first appeared in the print edition on January 16, 2021 under the title ‘Vaccine plus’. The author, cardiologist and epidemiologist, is President of the Public Health Foundation of India (PHFI) and author of Make Health in India: Reaching a Billion Plus. Views are personal