Explainer: Reaching herd immunity in a viral pandemic
Category: News & Politics
Via: tessylo • 4 years ago • 11 commentsBy: Manas Sharma, Simon Scarr and Jane Wardell, Reuters
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Explainer: Reaching herd immunity in a viral pandemic
FILE PHOTO: Coronavirus disease (COVID-19) outbreak in StoneBy Manas Sharma, Simon Scarr and Jane Wardell
SYDNEY (Reuters) - The novel coronavirus pandemic has brought "herd immunity" to the public consciousness, kindling hope the phenomenon can help slow or even end the outbreak.
Herd immunity refers to a large portion of a community developing a degree of immunity to a virus, thereby reducing person-to-person spread. As a result, the whole community gains protection, not just those who are immune.
(Click here for a Reuters graphic on how a vaccine slows the spread of a virus https://graphics.reuters.com/HEALTH-CORONAVIRUS/HERD%20IMMUNITY%20(EXPLAINER)/ygdvzmqqgpw/index.html)
There are two pathways to herd immunity: natural infection or vaccination.
Natural infection refers to when a large number of people have had a disease and recovered. However, the extent of protection via natural infection is unknown with the new coronavirus. Moreover, more people would die while waiting for herd immunity than if a vaccine was produced.
"The risk is not acceptable," said Catherine Bennett, epidemiology chair in the Faculty of Health at Melbourne's Deakin University. "We can't afford to have people infected to reach herd immunity when we know so little about the longer-term effects."
Vaccination can provide widespread immunity faster and more reliably.
There is no vaccine for COVID-19 - the disease caused by the novel coronavirus - though trials at different stages are underway around the world. It usually takes several years for a vaccine to be identified, tested, produced and distributed for public use. Vaccine makers hope to dramatically compress that timeline for COVID-19 through faster trials and by manufacturing at scale even before products have proved successful.
Experts believe if no other measures are taken, herd immunity could kick in when 50% to 70% of a population gains immunity through vaccination. The precise level depends on the vaccine's efficacy rate, which experts say will be 70% at best.
BALANCING VACCINE DISTRIBUTION
How a vaccine is distributed has implications for effectiveness. If shared unevenly - for example, if the wealthy have greater access than those in poorer locations - that would create safe clusters but leave large areas of susceptible people.
In the early stages of distribution, higher priority may be given to healthcare workers and others on front lines, or those considered most vulnerable - a process known as targeted vaccination. That risks missing people who might be considered "super spreaders", such as public transport workers.
"We need to be sure that we spread the vaccine equitably through the population," said Joel Miller, a senior lecturer in applied mathematics at La Trobe University in Melbourne, who uses mathematical models to help governments and non-profit organisations formulate policies to control infectious diseases.
MOVEMENT RESTRICTIONS
The movement of people also has implications for the spread of a virus.
At lower vaccination levels, the number of people who eventually become infected is similar in a group of people who mix and travel widely, and a group of people who are relatively static. However, the spread is much slower in a static population, hence governments worldwide imposing lockdown measures.
Even when a high percentage of the population is vaccinated, infection numbers can be reduced further if people refrain from travel.
WHILE WE WAIT
The new coronavirus is spread primarily via droplets expelled when a person coughs, sneezes or even talks.
Until a vaccine is developed, wearing masks, physical distancing and hand hygiene can help reduce transmission and contribute to creating herd immunity.
Epidemiologists largely agree that a combined approach is critical given early vaccines brought to market will likely not have 100% efficacy.
"It's about adding layers," said Deakin University's Bennett. "It gives us extra protection from community spread. The situation is very much better in places where a combination of measures is being used."
(Writing by Jane Wardell; Editing by Christopher Cushing)
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There are two pathways to herd immunity: natural infection or vaccination.
Natural infection refers to when a large number of people have had a disease and recovered. However, the extent of protection via natural infection is unknown with the new coronavirus. Moreover, more people would die while waiting for herd immunity than if a vaccine was produced.
"The risk is not acceptable," said Catherine Bennett, epidemiology chair in the Faculty of Health at Melbourne's Deakin University. "We can't afford to have people infected to reach herd immunity when we know so little about the longer-term effects."
Vaccination can provide widespread immunity faster and more reliably.
If you run the numbers, herd immunity would require 70 - 80% infection among the population, with the current fatality rate, we are looking at around 6.8 million deaths to reach herd immunity.
Unacceptable for all except the most extreme right wingers, and probably Trump.
Tried in Sweden, and their economy is still in the shitter last I read.
In another article, it was stated that Sweden is the model of HOW NOT TO HANDLE A PANDEMIC LIKE CO-VID
Did the Trump led approach get honorable mention in that article?
To beat this virus, all it would have taken was leadership, and we got shit from the WH.
No their economy held up better than many that had strick lock downs and they are down to about one death a day. The data looks good.
And we're still getting nothing from the 'president'.
Not so fast there Tex..... You might want to hold off on taking that victory lap with Sweden so quickly....!
In mid-June, Andersson said it was possible that Sweden had reached the bottom of the downturnn, as the government had revised their forecast to a -6% GDP downturn in GDP and an unemployment level of 9.3% (down from -7% and 11% respectively in their previous forecast) although they expected unemployment to further increase in 2021 to 10.3%. However, she cautioned that there was still a big uncertainty regarding the numbers. Similarly, the National Institute of Economic Research also revised their forecast downwards, to a -5.5% fall in GDP and for unemployment to increase to 8.5% during 2020, with a further increase up to 10% in 2021
As far as cases & deaths:
Noting the recent drop in the daily tally of COVID-19 cases, Tegnell observed on August 9, "Exactly why this happened at that time and why it was so quick and sudden, is difficult for us to understand." Tegnell acknowledges that the results of antibody blood tests do not find that enough Swedes have been infected and recovered to confer herd immunity as would be conventionally expected by epidemiologists.
How has Sweden fared in comparison with its Nordic neighbors that chose more comprehensive interventions? As of August 11, COVID-19 cases in Denmark, Norway, and Finland amounted so far to 14,959, 9,712, and 7,623, respectively; deaths per million are at 107, 47, and 60, respectively. In Sweden, cases stood at 83,126 and deaths per million at 571. In the U.S., meanwhile, cases totaled 5,265,034 with deaths per million were at 503.
Besides.... I though you hated socialists Dean?
Actually yes. It was mentioned.
They couldn't afford to do that without the billions of dollars they are getting from the government through Operation Warp Speed .
The most optimistic projections are that stringent adherence to social distancing practices would cut the number of fatalities in half. Social distancing isn't a panacea, either.
The sorcerer's stone of a vaccine is intended to provide artificial herd immunity in the same manner as natural herd immunity. The vaccine is intended to avoid the risk of severe COVID symptoms. But for those less vulnerable to developing severe COVID symptoms, there isn't really a difference between artificially induced immunity and naturally induced immunity. Before modern vaccines were available, the common practice was to expose children to common diseases, like measles, mumps, and chicken pox, to develop immunity. But planning for the infection meant the children were monitored and well cared for. The practice of developing natural immunity wasn't uncontrolled.
A vaccine achieving 70 pct efficacy is likely an over optimistic hope rather than a reliable predictor. And the projections are that a vaccine providing herd immunity, based on overly optimistic efficacy, would still require many months to achieve. The pandemic will likely continue well into next year.
The politicization of the pandemic has created expectations that can't be satisfied. At this point, whatever approach is taken by government to respond to the pandemic will almost certainly fail to satisfy unrealistic political expectations. Social distancing can only slow spread of the virus; the number of infections will continue to increase. Deploying a vaccine will encounter all sorts of logistical problems that will prevent quickly ending the pandemic. So far, the political expectations that have been raised are designed to fail.
tRump politicized this. No one else.
Co-vid 19 is not a political issue.