Covid-19 protection: Herd immunity vs vaccines – what will work? Wall Street Journal

In March, it was speculated that if the epidemic runs largely unchecked in South Africa through winter – the great majority of younger and healthy people would get the virus, develop only mild symptoms, and recover. They would thereby attain a degree of immunity which would, in aggregate, provide herd immunity to the broader society. This would have the potential to bring a sustainable end to the pandemic in South Africa. The concept of herd immunity has been put to the test in Sweden, which has had relaxed approach to the coronavirus outbreak. While the rest of the world was imposing national lockdowns, Sweden chose not to. Herd immunity means that enough people in a population have become immune to the virus — either through vaccine or previous infection — that the risk of new infections lowers across the board. In other words, the idea was, if Sweden kept its bars and restaurants open, more people among the less vulnerable would develop immunity and ultimately slow the spread. At first, Sweden's controversial approach appeared to be working. However, the country's eventual death toll, which greatly exceeds that of its Nordic neighbours, means Sweden has provided a cautionary tale. – Nadya Swart.What it would take to reach herd immunity .We know that Covid19 spreads through close contact, making crowded areas potentially deadly. But when some members of a crowd are immune, that begins to change. This is called herd immunity. It's what's protecting much of the population from diseases like measles and polio, and it's what's driving vaccine efforts today. .___STEADY_PAYWALL___.Read Also: Only herd immunity can control Covid-19 in SA – James Myburgh. MUST READ!.Dr Ashish Jha, Director at the Harvard Global Health Institute, says the notion is that there will be enough people in that community who are immune so that when you go to pass the disease on, you won't be able to pass it on in a way that it will propagate. .Economies around the world could then safely reopen, and some say it could put an end to the pandemic. But the path to herd immunity includes big hurdles. And experts say it could take years or more – if we get there at all. We'll explain. When scientists want to determine how fast a virus might spread, they look at its reproduction number. This represents how many people could catch the virus from a single infected person when no one in the population is immune. .David Dowdy, an Associate Professor of Epidemiology at John Hopkins University, explains that that helps us to understand how much additional immunity or other measures we need to implement in place to start to bring this epidemic under control as opposed to having it expand over time..For example: for the polio virus, one infected person will pass the disease to five to seven people – on average – and from there, the disease will spread exponentially. For the novel coronavirus, scientists say an infected person will likely spread it to two to four other people..According to Dowdy, that number can go down as more people become immune or (also) in response to measures like wearing masks and social distancing. .When enough people in a population gain immunity, the chances of infecting others goes down. .And once it falls below a certain point, it becomes harder and harder for the virus to spread. As a result, the majority of the community becomes protected – not just those who are immune. .Over time, the virus dissipates and really essentially goes away or circulates at very low levels in that community, says Dr Jha..Scientists say there are two ways the population can reach herd immunity: through broad infection or, more commonly, vaccination. To get there through infection – the majority of a population needs to get sick from a virus and develop molecular defences like antibodies that fight off the disease. But this method would be deadly. Experts estimate that less than 5% of people worldwide have had Covid-19. Yet, scientists say, to reach herd immunity – that number would have to be between 60 and 70%. .As Dr Jha explains: If we need to get to 60 or 70% infections – that's obviously more than four billion people getting infected. That would be tens of millions of people dying. It would be hundreds of millions of people getting very, very sick. It would be devastating – for the entire global population and for the economies – and it is wholly unnecessary. .There's also no guarantee that broad infection would lead to eradication. .According to Dowdy, we don't have many examples of complete immunity to viruses through natural infection, because people continue to get born in a population. So, every year you have a new set of babies who are born and they're going to be susceptible to that infection. .Experts say that the more efficient way to herd immunity is through vaccination. That's how scientists eradicated smallpox. .Dr Jha explains that because of vaccines, childhood mortality has dropped dramatically. Kids no longer die of measles, they don't die of a lot of the diseases that kids use to die of. Obviously, smallpox is one of the horrible scourges of humanity throughout the entire human history. We don't talk about smallpox anymore, because our vaccination campaign ultimately led to the eradication of smallpox. .But experts say they don't know enough about the coronavirus to predict the likelihood of reaching herd immunity and that there are large barriers to getting there – even with a vaccine. One challenge is that scientists don't yet know how long natural immunity might last. .Dowdy says that there's a big difference between being immune for six months and being immune for 10 years..For other respiratory viruses like the flu, antibodies tend to decrease over time. Scientists have observed this in some patients recovering from Covid-19, but there isn't enough data yet to be certain about what that means for immunity. How long a Covid-19 vaccine will last is still unclear, but it may be measured in months or years rather than a lifetime. Another challenge – not all vaccines in development will work the same and their effectiveness could differ. .The better a vaccine is in terms of the level of protection and the duration of protection, the further it gets you towards that point of herd immunity. .But even a less than perfect vaccine, if given to enough people in the population, can help reduce the spread, says Dowdy..Scientists are working quickly to test dozens of vaccines already in development, but it could take years to figure out which ones are more effective. So even if people get vaccinated, some could be more susceptible to catching the virus. But even as cases surge around the world, some experts are optimistic. .Read Also: Inside Covid-19: Good news on the Oxford vaccine – and enforced changes to spending habits. Ep 63.According to Dowdy, it is suspected that people who have gotten Covid-19 remain protected for many months at least, because we haven't seen a large number of repeat infections. We also know that it's possible to give people multiple vaccinations. So, I'm hopeful that we can develop – over time – a vaccine that, even if we do need to give multiple doses, will be highly effective in generating the levels of immunity that we need to beat this disease. .If this happens, global herd immunity may be possible. But until then, health experts have stressed that measures like social distancing and wearing masks will be key to slowing down the spread.

Covid-19 protection: Herd immunity vs vaccines – what will work? Wall Street Journal

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