We know that vaccines help people develop immunity to a virus or other germs. How does that happen? A vaccine introduces a less harmful part of a germ — or something created to look or behave like it — into a person’s body. The body’s immune system develops antibodies that fight that particular germ and keep the person from getting sick with it. Later, if the person encounters that germ again, their immune system can “recognise” it and “remember” how to fight it off. Rather than treating a disease after it occurs — like antibiotics or other drugs — vaccines are a preventive measure. It is estimated that they avert two to three million deaths every year by harnessing the power of our own bodies to keep us safe.

How will a vaccine prevent Covid-19?

The novel coronavirus that causes Covid-19 has spikes of protein on its surface that help the viruses attach to and enter human cells. Some of the coronavirus vaccines in development are designed to block the function of these protein spikes; others to prevent them from forming. An effective vaccine will protect a person who receives it by lowering their chances of getting Covid-19 if they encounter the coronavirus. Widespread vaccination for the coronavirus means that the virus will not infect as many people. This will limit spread through communities.

What types of vaccines are being developed?

There are several different types in development.

• Inactivated or weakened virus vaccines, which use a form of the virus that doesn’t cause disease but still generates an immune response.
• Protein-based vaccines, which use harmless fragments of proteins or protein shells that mimic the Covid-19 virus to generate an immune response.
• Viral vector vaccines, which use a virus that has been genetically engineered so that it can’t cause disease but produces coronavirus proteins to safely generate an immune response.
• RNA and DNA vaccines, a cutting-edge approach, that uses genetically engineered RNA or DNA to generate a protein that itself safely prompts an immune response.

When will a Covid-19 vaccine become available?

The vaccine will become available once it has been carefully tested and approved by regulating organisations such as the Federal Drug Administration (FDA) in the US or Drugs Controller General of India (DCGI) in India, manufactured in bulk and administered throughout the country. If there is strong enough scientific evidence that a vaccine is both effective and safe, emergency-use authorisation may be granted by regulating organisations. This will make the vaccine available as soon as reasonably possible. Once a vaccine is approved, scientists and doctors will monitor its use and, if necessary, adjust to improve it.

What is a cold chain?

The system for distributing medicines (also meat and chemicals) at low temperatures is known as the “cold chain”. The ultralow cold chain, the deep freeze, is the one maintained below –50°Celsius. There’s the “frozen” chain at –18°C, which is like a deep freezer in a home fridge. And then there is the refrigerated chain: many vaccines, such as the flu vaccine, are refrigerated between 2°C and 8°C in a fridge.

The vaccine manufactured by Pfizer must be kept at –70°C and once transferred to a refrigerator, it must be administered within five days. Transporting or storing Pfizer’s vaccines in India won’t be easy. The vaccines being developed by Astra Zeneca, Moderna, Bharat Biotech or Johnson & Johnson can be stored in a standard refrigerated chain (2°C-8°C ) for months.

Will the vaccines provide long-term protection?

It’s too early to answer that question. However, it’s encouraging that available data suggest that most people who recover from Covid-19 develop an immune response that provides at least some protection against reinfection — although we’re still learning how strong this protection is, and how long it lasts. It’s also not clear how many doses will be needed. Most Covid-19 vaccines being tested now are using two-dose regimens.

A few people have apparently had a second, often milder, case of Covid-19 and researchers are exploring what this means in terms of how long immunity lasts. Vaccine developers are looking at ways to boost the effectiveness of a vaccine so that it provides longer immune protection than a natural infection with the coronavirus.

Will people need an annual Covid-19 shot just like they do a flu vaccine?

It depends on whether Sars-Cov2 — responsible for Covid-19 — evolves quickly. As flu viruses are constantly mutating, last year’s vaccine may not protect you from this year’s viruses. New flu vaccines are released every year to keep up with rapidly adapting flu viruses.

Will mass vaccination bring about herd immunity?

When most people in a community are vaccinated against a disease, the ability of the pathogen to spread is limited. This offers a large section of people a sort of herd immunity, a useful by-product of mass vaccination. Herd immunity is really important to protect people in a community who are not or cannot be vaccinated, for example those with a compromised immune system, such as cancer patients. With Covid-19 raging around the world, only 10 per cent or fewer people have developed antibodies to the virus. To ensure herd immunity, an estimated 60 per cent at least would need to be immune to Covid-19. That will be possible only through vaccination.

Once you get vaccinated, would you still have to wear a mask and maintain physical distance?

Yes. While the vaccine may prevent you from falling ill we do not yet know if you can still carry and transmit the virus to others. That is why, until more is understood about how well the vaccine works, continuing with precautions such as physical distancing and wearing a mask will be important.

SOURCES: World Health Organization, Centers for Diseases Control and Prevention, US, Johns Hopkins Medicine, US