iCliniq logo

Ask a Doctor Online Now

HomeHealth articlesdelta variantIs a Booster Dose Necessary For Delta and Other Variants?

Is a Booster Dose Necessary For Delta and Other Variants?

Verified dataVerified data
Is a Booster Dose Necessary For Delta and Other Variants?

4 min read


Read this article to know the effectiveness of COVID-19 vaccines against the different variants of COVID-19.

Medically reviewed by

Dr. C. Elanchezhian

Published At August 11, 2021
Reviewed AtJanuary 29, 2024

Delta Variant of SARS-CoV-2

The delta variant of the coronavirus was first recorded in India in January 2021. The delta variant is a problem of concern for two main reasons: the increased rate of transmissibility and the degree of severe illness caused by it. Of the daily cases in the United States, about 82 percent were caused by delta variants, and in the United Kingdom, delta variants accounted for about 99 percent of cases. The Chinese Academy of Medical Sciences has stated in a study that the viral load in the delta variant is 1000 times higher than that of previous variants of SARS-CoV-2.

How Effective Are Vaccines Against Delta and Omicron Variants?

Although no vaccine is 100 percent effective in preventing an infection, the rate of mortality and hospitalization is relatively reduced in people who have been fully vaccinated. Like other forms of COVID-19, the delta variant also has the same effect in terms of vaccination. Ascertaining the efficiency of COVID-19 vaccines against the delta variants has been difficult due to the limited availability of research data. Although only a few studies have been done to determine the efficacy of COVID-19 vaccines on delta variants.

Let us discuss the effect WHO-approved vaccines on the delta variants.

Pfizer Vaccine:

A study by public health England has reported that getting two doses of the Pfizer-BioNTech vaccine prevents delta variant infection by around 80 percent. In symptomatic cases, the efficiency is 88 percent, and in patients who need hospitalization, it is the highest at 96 percent.

A report by the journal Nature states that a single dose of the Pfizer vaccine hardly protects against the delta variant. On average, the efficacy level of the Pfizer vaccine ranges between 64 to 96 percent against the delta variants in fully vaccinated people.

Moderna Vaccine:

Few studies have reported that the level of antibodies produced by the Moderna vaccine in the case of the delta variant is higher than that produced in response to beta forms. On the other hand, it is lower when compared with the alpha variants of the virus.

Reports by the Canadian study indicate that the Moderna vaccine is 72 percent effective against the delta variant. Even a single dose of the Moderna vaccine provides good protection against the delta forms, and the protection is higher when the two doses of vaccine are taken. A few of the researchers in New York have reported that Moderna is equally effective as Pfizer, with an efficiency of about 94 to 95 percent when it comes to delta variants.

Johnson and Johnson Vaccine:

Clinical trials have proved the Johnson and Johnson vaccine to be 71 % effective against hospitalization due to delta variant infection and 96 % effective against death from delta variant infection.

AstraZeneca Vaccine:

The AstraZeneca vaccine administered in India in the name 'Covishield' has been proven to be the most influential vaccine against the delta variant, with an efficiency rate of 92 percent. No death cases among delta variants are reported in the people who have been fully vaccinated with the AstraZeneca vaccine.

Omicron Variant of SARS-CoV-2

Another variant of coronavirus that has emerged in South Africa was designated as a variant of concern by the WHO on November 26, 2021. Omicron was believed to be highly transmissible (no sources) but less severe and the number of COVID-19 cases started rising around the month of January. This variant exhibited the usual symptoms like fever, cough, fatigue, and loss of smell and taste. This wave was a combination of delta and omicron variants. It raised a lot of speculation regarding the vaccine’s efficiency against these two variants.

Effectiveness of Vaccines Against Omicron Variant

Vaccines are found to have great efficiency against Omicron infection. Studies suggest a booster dose along with the initial two shots, provides an efficiency of 86 %. Therefore, the vaccines will have an effect on the increased transmissibility suspected with the Omicron variant.

The COVID-19 pandemic is still hanging around the corner, raising speculation about the need for a booster dose. Let us briefly discuss what a booster dose is and why it is administered, and specifically, the current need for a COVID booster dose.

What Is a Booster Dose?

A booster dose, in general, refers to re-exposure to immunizing antigen by the administration of an extra vaccine in addition to the primary dose.

Why Is a Booster Dose Needed?

Depending on the number of specific antibodies, the need for a booster dose is evaluated. It is determined with the help of an anamnestic response, which assesses the antibodies produced following an antigen stimulus. If the number of specific antibodies is less, it cannot protect against the particular disease; thereby, the purpose of vaccination is not met.

Need for the COVID-19 Booster Dose:

Research carried out by the Israeli health ministry has stated that the protection against COVID-19 in people who had their vaccination in April 2021 is around 75 percent whereas, it is only 16 percent in people who got their vaccine in January 2021. It has posed the need for a booster; however, as of now, the Centers for Disease Control and Prevention has not approved the administration of booster doses for any vaccines. And, therefore on September 22, 2021, the FDA approved the use of a booster dose of Pfizer-BioNTech in individuals above the age of 18 years. And on October 20, 2021, the booster shot of the Moderna and Johnson & Johnson vaccine was approved. As of November 29, 2021, the Centers for Disease Control and Prevention (CDC) of the United States has further strengthened its recommendation to get the vaccine with the emerging Omicron variant of SARS-CoV-2.

The following table depicts when and who should take the booster shot of the COVID vaccines:

delta varient

Effect of Booster Dose Against the Delta Variants:

Recent trials have reported that the booster dose of the Pfizer vaccine has the ability to produce five times more antibodies in people between the age group of 18 to 55 years and eleven times more antibodies in people between 65 to 85 years. Pfizer-BioNTech, Moderna, and Johnson & Johnson have received approval from the CDC of the United States to administer the third dose to protect against the omicron, delta, and other new variants of the SARS-CoV-2 virus.

People have already started taking booster doses all over the world. The eligible candidates are advised to get the shots, to combat the increasing number of COVID-19 cases.

How to Protect Yourself From the Highly Contagious and Powerful Delta and Omicron Variant SARS-CoV-2 Virus?

As the cases of delta and Omicron variant COVID-19 are increasing in almost all parts of the world, it is high time we take adequate precautionary measures to protect ourselves and our loved ones from viral infection.

As like every other variant of COVID-19, the preventive measures to protect against COVID-19 infection are solely dependent on the following tetrad of factors:

Variant SARS-CoV-2 Virus


Vaccination is of prime importance at this time. However, it does not provide complete protection against the spread of infection, and it plays a vital role in reducing the chances of hospitalization and preventing deaths. Also, fully vaccinated people are comparatively less infectious than unvaccinated people, and the period of virus inhabitation in them is very low, leading to a decreased spread of infection. It eventually reduces the chain of spread and may serve as an effective tool to stop the persisting pandemic.

In addition to getting the vaccination at your turn, wearing masks while going out, maintaining a social distance of one meter or more, washing your hands frequently, and avoiding touching your nose, eyes, and mouth will help protect you from infection.

Frequently Asked Questions


How Can One Protect Themselves From Omicron?

The primary way to protect oneself from the Omicron variant is to wear a mask. The virus is highly contagious, and thus, social distancing is important. One can get vaccinated as soon as they can. Also, do not forget to take the booster dose. Everyone should use hand sanitizers and also avoid touching their face.


What Can Be Done to Stop the Spread of the COVID-19 Omicron?

One should be aware if they are infected with the variant or not. If infected, they should isolate themselves till they are healthy. As it is highly contagious, one should avoid being part of huge crowds or gatherings. Everybody should get vaccinated as soon as possible. Basic protocols of cleanliness should be followed.


How to Protect Oneself?

One should wear a tightly fitted mask that covers the nose and mouth properly. One must avoid social gatherings and also keep an adequate distance from people. Get vaccinated as soon as one can.


When Does the Omicron Variant Show Its Symptoms?

People should be aware that the time to develop the symptoms of this variant is shorter than the previous variants. It may show its symptoms from the second day of incubating the virus or after a week of incubation too. One has to be cautious and get themselves tested if in doubt.


What Is the Incubation Period for Omicron Variant?

Nobody shows the symptoms after getting infected right away. The period from when the virus enters the body till it shows the first symptom is known as the incubation period. The incubation period can be three days for the Omicron variant.


How Long Does A Person Stay Contagious After Testing Positive for the Infection?

Covid-19 infection is highly transmissible. The person infected by this contagious virus should stay quarantined by isolating themselves completely. One may stay contagious from ten days to 20 days. Immunocompromised people should stay quarantined for a few more days than people having healthy immunity.


What to Do at Night to Protect Oneself From the COVID-19 Infection?

When people are asleep, they cannot follow the protocols like covering the nose and the mouth while sneezing or coughing, so it should be avoided to share the same room or at least maintain an adequate distance to avoid spreading the virus.


Is It Possible to Avoid Getting Infected by Omicron Variant if Vaccinated?

Yes, it is possible to get infected by the Omicron variant even if vaccinated, but the good part is that vaccination protects a person from developing a serious stage of infection. One may show the symptoms, but it has been observed so far that one may not die from the variant if vaccinated. As new variants are coming into the virus, complete protection from the vaccination still needs to be clarified.


For How Many Days After Infection Will One Test Positive?

It is possible to test positive until the initial weeks of the infection. It is observed that it takes about three days to show the positive signs of the infection. It can last up to two to three weeks after being infected.


Does One Stay Contagious Even After a Week of Infection?

The Covid-19 variant is highly contagious and does not diminish soon from the body. It is always better to get oneself tested after a week of infection; if the test comes negative, the person is no longer a threat to other people.


When Is the Cold Transmissible?

One can transmit the cold even before the symptoms occur. The droplets or the aerosols are the medium of infection. If one has been suffering from a cold, it is better to avoid leaving the droplets anywhere and cover one’s mouth with a mask or use a handkerchief while sneezing or covering the mouth and the nose.


Which Is the Best Vaccine Against the Omicron?

It is so far impossible to pick a vaccine that is best for preventing the infection. Many studies are undergoing to study the efficacy of the vaccines against COVID-19 and its variants. But rather than debating about the best vaccines, getting vaccinated by whichever is available is better, as vaccination will provide basic immunity to the body.


What Sanitization Protocols Should Be Followed After Reaching Home?

People should discard the mask they were wearing to protect themselves from the virus outside the home or wash the reusable ones. They should wash their hands first, then their face. Change one’s clothes and wear clean and washed ones. Do not enter the house wearing the same footwear that was worn outside the house. Other basic protocols of safety can also be followed.


What Should Be Avoided if A Person Has COVID?

It is one’s responsibility to prevent other people from getting infected, so if one has covid, one should isolate oneself from everyone. Roaming outside and engaging in social gatherings should be avoided. Talking to people by getting near them or touching them should be avoided. Protocols of safety issued by the health department should be followed.


Are The People Naturally Immune to Omicron?

The body provides a person with immunity against every disease, but sometimes the disease or the infection penetrates the barrier of immunity, and one gets infected. So it cannot be said that we can be protected from getting Omicron naturally.
Dr. C. Elanchezhian
Dr. C. Elanchezhian

General Medicine


booster dosedelta variant
Community Banner Mobile
By subscribing, I agree to iCliniq's Terms & Privacy Policy.

Source Article ArrowMost popular articles

Ask your health query to a doctor online

Infectious Diseases

*guaranteed answer within 4 hours

Disclaimer: No content published on this website is intended to be a substitute for professional medical diagnosis, advice or treatment by a trained physician. Seek advice from your physician or other qualified healthcare providers with questions you may have regarding your symptoms and medical condition for a complete medical diagnosis. Do not delay or disregard seeking professional medical advice because of something you have read on this website. Read our Editorial Process to know how we create content for health articles and queries.

This website uses cookies to ensure you get the best experience on our website. iCliniq privacy policy