• Published on: Apr 19, 2020
  • 3 minute read
  • By: Dr Rajan Choudhary

What Is Herd Immunity With Respect To Covid19 ?

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Herd immunity: the basics

Many countries have been in lockdown for over a month, and some have tried to begin the discussion of an exit strategy. We know that remaining in lockdown continuously is not a feasible strategy, as many people have been suffering economic consequences from the stringent lockdown measures, and many countries have been providing significant monetary and fiscal support for people and businesses at risk. But leaving lockdown too early has its own consequences.

Almost all public health professionals will agree that the lockdown has been able to significantly reduce infection rates and reduce the pressure on our healthcare systems. By taking this early victory and prematurely ending lockdown we risk another wave of infections, reintroducing lockdown, and having an overall negative effect on the general health of the populous.

So what can we do? One exit strategy that has been touted recently is herd immunity. To understand how to may work for COVID we must understand what epidemiologists mean by herd immunity.

IMMUNITY

Our body’s immune system fights against invading organisms such as bacteria and viruses. For a more in-depth discussion you can have a look at previous blogs on Vaccines and Boosting the Immune system. The immune system is very competent and has mechanisms to theoretically recognise any protein tags that do not belong to that person’s cells, even protein tags that do not currently exist in nature. This gives the immune system the ability to theoretically recognise nearly any invading organism that has existed or will ever exist.

The immune system goes beyond this as well and produces “memory cells”. These remain in the blood after an infection for a long time; in some cases, it can even be lifelong. When a second infection occurs from the same organism the immune system jumps into action and is able to produce antibodies against the invader almost immediately. This can neutralise the invader before it has a chance to replicate, cause severe symptoms and harm the body. Sometimes we never realise we have been infected as the infection never gets a chance to cause any damage.

Importantly, if the invader cannot replicate in our body, then its ability to spread to other people is also reduced. For example, respiratory viruses can rapidly replicate in our lungs and be transmitted when we cough or sneeze. By eliminating the virus before it can replicate extensively the number of viral particles in each cough and sneeze is reduced, reducing the chances of another person catching the infection.

This is the basis of how vaccines work and is covered in depth in the two part blog.

HERD IMMUNITY

If our immune system is so competent, why do we need to worry about infections at all? Surely we can all get infected and gain immunity. In an ideal world where everyone was healthy this may be true. But there are many people who do not have fully functioning immune systems. These people are immunocompromised and can be for many reasons.

  • Chemotherapy and radiotherapy for cancer destroys rapidly dividing cells such as cancer cells. Unfortunately, it also hits other dividing cells, such as hair follicles, gut lining and the bone marrow, which produce the white blood cells that give us immunity. Chemotherapy patients are very susceptible to even the mildest of infections. Even if a mild infection is suspected, they are treated aggressively with antibiotics, as their lowered immune systems can become overwhelmed very quickly.
  • Sometimes doctors advise patients to take medication that purposefully dampens the immune system. This is necessary for transplant patients, where the host immune system attacks the donor organ as it does not belong to the host, or in autoimmune disorders, where the immune system attacks the host by mistakenly recognising it as an “invader”.
  • Taking steroids long term has a similar effect, and is used quite commonly for skin disorders, asthma, COPD, and other inflammatory conditions.
  • People with various chronic illnesses can have reduced immunity as a result of the illness. High sugar levels associated with poorly controlled diabetes can cause worsening organ function, including the immune system. These patients are more susceptible to infections.
  • Finally, some people do not have fully functioning or welldeveloped immune systems for a variety of reasons, inherited or acquired. As we get older, the immune system function decreases, and simple infections can be devastating.

In all of these cases the ability to recognise invading organisms, destroy them and form immunity is hampered. Vaccination, one way of inducing immunity without causing the person to suffer from a full-blown infection, can also be ineffective in these patients, and some vaccines can be dangerous if used incorrectly. So how do we protect these vulnerable patients?

HERD IMMUNITY

This is where we go back to the earlier point. Immunity in healthy people can reduce or even prevent the spread of infection from one person to another. The number of healthy people outnumber the number of vulnerable, immunocompromised ones. Therefore, if we induce immunity in most people, the infection will simply not spread to the vulnerable ones. We don’t have to immunise everyone, just enough to prevent transmission. This is called herd immunity. This is why we immunise everyone with flu vaccines even those that are healthy and will survive a full blown infection. Because by preventing these people from inadvertently spreading the flu, they will protect those that we cannot immunise.

Does herd immunity work? For most other diseases, yes. It depends on how the disease is spread, and how infective it is. For measles, you need to immunise 19 out of 20 people to achieve herd immunity, because it is so infective. But once herd immunity was achieved death rates were drastically reduced. With the advent of anti-vaccine campaigns, particularly against MMR, this herd immunity has been lost, and many vulnerable children (and adults) who do not have fully functioning immune systems are now contracting this virus and dying from a preventable disease.

It can be achieved for pandemics as well. Norway was able to achieve partial herd immunity to H1N1 (swine flu) through a vaccination program and natural immunity. Vaccines are the best method for achieving herd immunity without extremely high death rates. We have already covered the issues with making a vaccine, and why it takes such a long time, in our previous blog

From reading this blog you should now have an understanding of what herd immunity is, and why it is important in protecting those that are vulnerable to infections. In our next blog we will look at why herd immunity may not be the solution for COVID-19.

Dr Rajan Choudhary, UK, Chief Product Officer, Second Medic Inc

www.secondmedic.com

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CRP Test Meaning and When to Do It

CRP Test Meaning and When to Do It

If you’ve recently had blood work or your doctor suspects an infection or inflammation, they may have recommended a CRP test. But what is it? Why is it important? And when exactly should you get it done?

Let’s simplify the medical jargon and walk you through the CRP test meaning and when to do it, especially in the Indian healthcare context.

 

What Is a CRP Test?

CRP stands for C-reactive protein. It is a substance produced by your liver in response to inflammation in the body.

The CRP test is a blood test that measures the amount of C-reactive protein in your blood. High levels of CRP usually mean there’s inflammation in your body, which could be due to an infection, injury, or a chronic disease like arthritis.

High CRP = Inflammation Alert

This test doesn’t tell you what’s causing the inflammation—it simply tells you that something is wrong, and further testing might be needed.

 

What Does the CRP Test Detect?

While CRP is a general marker, it is helpful in detecting:

  • Bacterial or viral infections
     

  • Autoimmune disorders like rheumatoid arthritis or lupus
     

  • Inflammatory bowel diseases
     

  • COVID-19 severity
     

  • Heart disease risk (especially with high-sensitivity CRP or hs-CRP)
     

 

When Should You Do a CRP Test?

You should get a CRP test done when:

  1. You have fever or chills that won’t go away
     

  2. You’re showing signs of infection like cough, swelling, or pain
     

  3. Your doctor is monitoring an autoimmune disease
     

  4. You’re recovering from surgery or injury
     

  5. Your doctor is checking inflammation due to chronic disease
     

  6. You are showing COVID-like symptoms (to assess severity)
     

 

Normal CRP Levels:

CRP Level

Interpretation

Below 1 mg/L

Low risk of inflammation

1–3 mg/L

Moderate risk

Above 3 mg/L

High inflammation or infection present

Above 10 mg/L

May indicate serious infection or disease

Note: For heart disease risk, a high-sensitivity CRP (hs-CRP) test is used.

 

Is Fasting Required for the CRP Test?

No, fasting is not required. You can take the CRP test at any time of day, unless it is being done with other tests that require fasting (like blood sugar or cholesterol).

 

Lab Tests Packages Including CRP

You can book a CRP test alone or as part of a health package via SecondMedic.com, powered by Thyrocare:

Basic CRP Test

  • Detects inflammation/infection
     

  • Simple blood draw
     

  • Home sample collection
     

COVID Monitoring Panel

  • CRP, D-Dimer, Ferritin, CBC
     

  • Recommended if you have COVID symptoms or are recovering
     

Inflammation Panel

  • CRP + ESR + CBC + Liver Profile
     

  • For those with chronic fatigue, joint pain, or autoimmune diseases
     

 

Lifestyle Tips If Your CRP is High

A high CRP may indicate ongoing inflammation. Along with medical treatment, here are some tips:

  • Eat more fruits, vegetables, and whole grains
     

  • Cut down on sugar and processed food
     

  • Include omega-3 rich foods like flaxseed and fish
     

  • Exercise regularly
     

  • Manage stress and sleep better
     

  • Quit smoking and limit alcohol
     

 

5 Most Asked Questions About the CRP Test

1. What is the CRP test used for?

CRP tests are used to check for inflammation due to infections, autoimmune diseases, and to monitor treatment effectiveness.

2. What causes a high CRP level?

Infections, chronic inflammation, surgery, injuries, and lifestyle diseases like diabetes and heart disease.

3. Is a CRP test painful?

No. It’s a simple blood test and usually takes just a few minutes.

4. How long does it take to get CRP test results?

Most labs deliver CRP results within 24 to 48 hours.

5. Can CRP levels return to normal?

Yes, with proper treatment and lifestyle changes, CRP levels can go back to the normal range.

 

Booking a CRP Test Online (Thyrocare via SecondMedic)

Here’s how you can book it:

  1. Go to www.secondmedic.com
     

  2. Search for "CRP Test – Thyrocare"
     

  3. Select home sample collection
     

  4. Enter your location and schedule pickup
     

  5. Get digital results within 1–2 days
     

 

Conclusion

The CRP test is a simple, affordable, and powerful tool to detect inflammation early. Whether you’re dealing with an infection, monitoring a chronic condition, or recovering from illness, this test gives your doctor a clearer picture of what’s happening inside your body.

Don’t ignore signs like unexplained fever, fatigue, or body pain. Get tested.

If you’re wondering about CRP test meaning and when to do it — the answer is simple: whenever inflammation or infection is suspected, this test is your body's alert system.

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