Why Vaccines May Not Be Able to Eliminate Covid-19: QuickTake

Photographer: Akos Stiller / Bloomberg

The road to eliminating Covid-19 is long and paved with uncertainty. Many countries rely on vaccines to build up enough immunity in their populations so that SARS-CoV-2 cannot find susceptible people to infect, slowing and eventually halting the transmission of the coronavirus. But even with the introduction of highly effective vaccines, immunization coverage may not reach that level – the so-called herd immunity threshold – shortly. For a start it is not known what level of immunity is required and whether vaccines will be powerful enough to achieve it. There is also the threat of it emerging coronavirus variants that can weaken the effectiveness of immunizations.

1. Can Covid-19 be eradicated?

No. Up to now only one human disease – smallpox – is official exterminated; that is, reduced to zero cases and kept there for the long term without continuous intervention measures. Smallpox was eradicated thanks to a highly effective vaccine and the fact that humans are the only mammals naturally prone to infection with the variola virus that causes the disfiguring, sometimes fatal disease. Humans are the only known reservoir of it polio virus, but it is still spreading a few countries, which caused crippling diseases, despite the widespread use of effective immunizations and a 32-year-old global eradication effort. SARS-CoV-2 is thought to persist in horseshoes in nature bats, and are known to infect mink, cats, gorillas, and other animals. In order to eradicate the virus, it would have to be banned from any susceptible species, which is not feasible. In countries that have successfully suppressed Covid-19 cases, Instead, elimination of the disease has been suggested.

2. What is elimination?

It’s when attempts to quell an outbreak have resulted zero new cases of disease or infection in any area over an ongoing period. There is no official definition of how long that should be. One proposal is to make it 28 days, which is twice as long as the outer range of the SARS-CoV-2 incubation period – the time between infection and the onset of symptoms. Some countries, such as New Zealand, have achieved zero new cases over long periods using border closures, lockdowns and careful case tracing and isolation. During a pandemic, an outbreak of a new infection on all continents, supporting the elimination of every infectious disease across the country challenging, if not impossible, due to the threat of the virus re-entering the country from infected international travelers.

3. Will vaccines eliminate Covid-19?

It’s hard to tell. It is not known what a section of the population needs immunity to prevent the coronavirus from circulating, or even the most powerful vaccines to prevent its spread. One study estimated that to stop the transfer, 55% to 82% of the population would require immunity, which can be achieved by recovery from infection or vaccination. Herd immunity was not reached in Manaus, the capital of the Amazonas state of Brazil, even after an estimated 76% of the population was infected. Still, there is reason to believe that mass inoculations will have a more potent effect, as vaccines appear to provide stronger and more durable protection than a previous infection.

4. How effective will vaccines be?

There is good evidence that the recordings were made by Pfizer Inc.-BioNTech SE and Moderna Inc. is very effective – as much as 95% – in preventing recipients from developing Covid-19 themselves. However, no data has been released on their ability to prevent people from developing asymptomatic infections or passing the virus to others. The gold standard in vaccinology is to stop both infection and disease, through so-called sterilizing immunity. But it is not always achieved. For example, the measles vaccine prevents infection so that vaccinated people don’t spread the virus, while the vaccine takes care of it Whooping cough protects well against serious illness, but is less effective at stopping infection. Encouraging is one Study of Moderna’s Covid vaccine in monkeys suggested that it would reduce, if not completely prevent, the further transmission of the virus. Clinical trials with The AstraZeneca Plc vaccine indicates that it may be less than 60% effective in stopping infections – making herd immunity unlikely to be achieved, even if everyone in a population receives two doses.

5. How do variants of the virus play a role?

Researchers have studied the ability of antibodies in the blood of recovered Covid-19 patients to block the new, rapidly spreading variants B.1.1.7, 501Y.V2 and P.1 that were first reported in the UK, South Africa and Brazil. Some studies have shown that these strains may be able to escape the immune protection afforded by natural infection. The scientists cautioned that the lab studies are only indicative and there is no evidence that this actually happens in the community, or that antibodies generated by vaccines will be less effective against the new strain.

6. Should Covid-19 Vaccines Prevent Infection to Curb Cases?