How will we know we've reached herd immunity?

ASEAN NOW Content Team · February 18, 2021

Health officials around the world are racing to vaccinate enough people to stop the spread of COVID-19, but what qualifies as "enough" is still an open question.

The goal is to get to "herd immunity," which is when enough people have immunity, either from vaccination or a past infection, to stop uncontrolled spread.

Herd immunity doesn’t make any one person immune, and outbreaks can still flare-up. It means that a virus is no longer easily jumping from person to person, helping to protect those who are still vulnerable to catching it.

Nobody knows for sure what the herd immunity threshold is for the coronavirus, though many experts say it’s 70% or higher. And the emergence of variants is further complicating the picture.

Here’s what’s known about the virus and herd immunity.

HOW IS THE HERD IMMUNITY THRESHOLD CALCUATED?

It's a formula based on how contagious a virus is — or how many people catch the virus from one infected person, on average.

But the calculation offers only a broad target for when there might be a big drop off in spread. The figure could also vary by region.

"It’s not 64.9 is terrible and 70.1 is fantastic," said Dr. Walter Orenstein, an infectious disease expert at Emory University.

Orenstein notes vaccination levels and other factors that affect spread could differ even within a city.

HOW DO WE KNOW WE'VE REACHED HERD IMMUNITY?

Proof that we're nearing herd immunity would be a "disruption in the chain of transmission," said Ashley St. John, who studies immune systems at Duke-NUS Medical School at Singapore.

But don't wait for any big declaration that we’ve reached that milestone.

To determine whether to relax restrictions, health officials will be watching infection and hospitalization trends as vaccinations roll out. And those decisions are likely to begin long before the ideal herd immunity threshold is reached, though they will be gradual and vary by region.

In India, for instance, scientists believe that more people will need to be protected in densely populated cities, where the virus spreads faster, than in its vast countryside.

India plans to look for antibodies in people nationally to figure out what percentage of its nearly 1.4 billion people have already been infected, said Dr. Jayaprakash Muliyil, who is advising the government on virus surveillance.

Vaccine effectiveness also plays a role. Fewer people need to be vaccinated to achieve herd immunity if the shots have higher efficacy.

HOW DO CORONAVIRUS VARIANTS AFFECT HERD IMMUNITY?

It depends on the protection that past infection or vaccination gives you from the variant.

If vaccines were to prove notably less effective against a variant, it would require vaccinating an even greater portion of the population or updating existing vaccines to make them more effective, Orenstein said.

So far, it appears the shots provide at least some protection from the most worrisome variants. But scientists are still studying the situation, and worry about further mutations.

The variants have underscored the importance of vaccinating people as quickly as possible. Slowing transmission is critical since viruses can mutate when they infect people.

FULL ARTICLE

pikao · February 18, 2021

Did we ever have "herd immunity" against:

Influenza (having vaccines since decades)

Dengue

Zika

HIV

Malaria

Ebola

Herpes

Hepatitis

Yellow fever...........

the list goes on forever, it is like it is and population is still growing

I do not really understand the question

RichardColeman · February 18, 2021

12 minutes ago, pikao said:

Did we ever have "herd immunity" against:

Influenza (having vaccines since decades)

Dengue

Zika

HIV

Malaria

Ebola

Herpes

Hepatitis

Yellow fever...........

the list goes on forever, it is like it is and population is still growing

I do not really understand the question

I think the odds of coughing in a crowded room and passing on HIV is pretty remote !

pikao · February 18, 2021

Many common infections can spread by airborne transmission at least in some cases, including but not limited to: COVID-19;^[12]measles morbillivirus, chickenpox virus;^[4]Mycobacterium tuberculosis, influenza virus, enterovirus, norovirus and less commonly coronavirus, adenovirus, and possibly respiratory syncytial virus.^[

pikao · February 18, 2021

50 minutes ago, RichardColeman said:

I think the odds of coughing in a crowded room and passing on HIV is pretty remote !

In a "Dark Room" maybe, but jokes aside, fear and panic have never been good advisers

Kwasaki · April 6, 2021

On 2/19/2021 at 2:42 AM, pikao said:

Did we ever have "herd immunity" against:

Influenza (having vaccines since decades)

Dengue

Zika

HIV

Malaria

Ebola

Herpes

Hepatitis

Yellow fever...........

the list goes on forever, it is like it is and population is still growing

I do not really understand the question

Well covid 19 is not the same as ordinary flu's and depending where you went abroad you have to have Herpes and Yellow fever thought that was pretty obvious.

Tingtong69 · April 12, 2021

Thailand chose the two least efficacy vaccines. Let's be generous and say Thai vaccinations are 70% effective.

And 70% of population receives their jabs by November (not looking likely)

That wd mean only 56% are effectively protected for the next tourist season.

Excel · April 12, 2021

On 2/19/2021 at 2:42 AM, pikao said:

Did we ever have "herd immunity" against:

Influenza (having vaccines since decades)

Dengue

Zika

HIV

Malaria

Ebola

Herpes

Hepatitis

Yellow fever...........

the list goes on forever, it is like it is and population is still growing

I do not really understand the question

I think it should better be described as Flock immunity. This appears to have been achieved already by Bangkokians as witnessed rushing back to their villages like sheep in the last few days.

Maha Sarakham · April 12, 2021

8 hours ago, Excel said:

I think it should better be described as Flock immunity. This appears to have been achieved already by Bangkokians as witnessed rushing back to their villages like sheep in the last few days.

Beer, loud music, and partying with friends - of course they went back!

tonray · April 13, 2021

15 hours ago, Tingtong69 said:

Thailand chose the two least efficacy vaccines. Let's be generous and say Thai vaccinations are 70% effective.

And 70% of population receives their jabs by November (not looking likely)

That wd mean only 56% are effectively protected for the next tourist season.

Virus Math ?

rumak · April 15, 2021

On 2/19/2021 at 2:42 AM, pikao said:

Did we ever have "herd immunity" against:

Influenza (having vaccines since decades)

Dengue

Zika

HIV

Malaria

Ebola

Herpes

Hepatitis

Yellow fever...........

the list goes on forever, it is like it is and population is still growing

I do not really understand the question

Hepatitis C has VERY effective medicines that kill the virus by taking one pill a day for 90 days. Done. Gone. This has been approved and available for about 5 years.

Hep C is a very serious disease. The cures are VERY expensive.

Some very rich people whose names are in the news constantly about their "humanitarion efforts" could easily pay for enough doses to eradicate hep c. Silence

Hypocrisy is definitely the most deadly disease affecting the world as we know it

Edited April 15, 2021 by rumak

techietraveller84 · April 15, 2021

What happened to the title of this thread? Is it just me, or is something a bit off?

Quote

because of virus outbreak CORONAVIRUSPublished 18 hours ago How will we know we've reached herd immunity?

Yellowtail · April 16, 2021

15 hours ago, rumak said:

Hepatitis C has VERY effective medicines that kill the virus by taking one pill a day for 90 days. Done. Gone. This has been approved and available for about 5 years.

Hep C is a very serious disease. The cures are VERY expensive.

Some very rich people whose names are in the news constantly about their "humanitarion efforts" could easily pay for enough doses to eradicate hep c. Silence

Hypocrisy is definitely the most deadly disease affecting the world as we know it

While I generally agree with you about the hypocrisy, many/most people that have Hep C have it for twenty years before they find out they have it. Only about half the people that have Hep C ever have any symptoms.

rumak · April 16, 2021

1 hour ago, Yellowtail said:

While I generally agree with you about the hypocrisy, many/most people that have Hep C have it for twenty years before they find out they have it. Only about half the people that have Hep C ever have any symptoms.

Think about it . Almost everyone gets a blood test from time to time. It is very simple and inexpensive to look for hep c when doing a blood test, general health screening or for a specific reason. CDC : CDC now recommends universal hepatitis C screening for all U.S. adults and all pregnant women during every pregnancy,

yes, in many cases it takes years for symptoms to appear. BUT," Globally, an estimated 71 million people have chronic hepatitis C virus infection. A significant number of those who are chronically infected will develop cirrhosis or liver cancer."

71 million people ! A pill a day for 12 weeks and its gone. Where are the "save the world" vaccine billionaires ??

Yellowtail · April 16, 2021

6 minutes ago, rumak said:

Think about it . Almost everyone gets a blood test from time to time. It is very simple and inexpensive to look for hep c when doing a blood test, general health screening or for a specific reason. CDC : CDC now recommends universal hepatitis C screening for all U.S. adults and all pregnant women during every pregnancy,

yes, in many cases it takes years for symptoms to appear. BUT," Globally, an estimated 71 million people have chronic hepatitis C virus infection. A significant number of those who are chronically infected will develop cirrhosis or liver cancer."

71 million people ! A pill a day for 12 weeks and its gone. Where are the "save the world" vaccine billionaires ??

Not sure why a healthy person under fifty would be having a blood test but I agree, people should be tested.

That said, about half the people that have Hep-C NEVER have any symptoms, live long lives and never know they have it.

It generally takes 20 years for anyone to develop symptoms.

Not sure about the new medications, but the medications ten years ago had significant unpleasant side effects and were not more that 50-80% effective depending on genotype.

At that time, the medication alone was about US$35,000, no idea what it might cost now, but it has likely come down.

rumak · April 16, 2021

2 hours ago, Yellowtail said:

At that time, the medication alone was about US$35,000, no idea what it might cost now, but it has likely come down.

the reason you are not aware of the new medicines is because hep c is one of those little secrets that people don't talk about. Go to a website where many sufferers tell their sad stories, and how the new medicines (start with Google : new hep c drugs) are often denied by insurers...... and the COST is around 100k US DOLLARS ! for the ninety pills.

Not sure why you are pursuing this as you are not experienced on this subject,

and yet you continue to miss the point that this serious illness CAN BE cured but the price is way beyond what ordinary people can pay............. and drug companies,governments,

and well known "philanthropists" just don't give a hoot

hypocrisy ! Now, back to the all important Covid madness gripping the world

Yellowtail · April 16, 2021

7 hours ago, rumak said:

the reason you are not aware of the new medicines is because hep c is one of those little secrets that people don't talk about. Go to a website where many sufferers tell their sad stories, and how the new medicines (start with Google : new hep c drugs) are often denied by insurers...... and the COST is around 100k US DOLLARS ! for the ninety pills.

Not sure why you are pursuing this as you are not experienced on this subject,

and yet you continue to miss the point that this serious illness CAN BE cured but the price is way beyond what ordinary people can pay............. and drug companies,governments,

and well known "philanthropists" just don't give a hoot

hypocrisy ! Now, back to the all important Covid madness gripping the world

The reason I am not aware of the new medicines is because I cleared the virus in 2011 after six months or Interferon/Ribavarin therapy. I paid US$35K the drugs, which seemed like a good value when I was looking at getting on a waiting list for a liver transplant. My sad story is on one of those websites where I went for support while going through treatment, and I don't think I ever fully recovered from some of the side effects.

I agree with the hypocrisy of the left, but again, about half the people with Hep-C will live there entire life and never suffer any symptoms.

Hep-C is also not easily transmitted. I had it for thirty years, and was married for ten years before I found out I had it and my wife never got it.