Home COVID-19 COVID-19 Vaccine Updates FAQ on COVID -19 Vaccines

FAQ on COVID -19 Vaccines

1. What are the different types of COVID -19 vaccines likely to be available for use in near future?

mRNA, Vector vaccines and Inactivated vaccines are likely to be made available for use in near future.

a. mRNA vaccine

(Pfizer-BioNTech vaccine and Moderna vaccine)

It consists of messenger RNA molecules of the virus which code for parts of the target pathogen that are recognized by our immune system (‘antigens’). Inside our body’s cells, the RNA molecules are converted into antigens, which are then detected by our immune cells to produce antibodies.

b. Vector vaccine

(ChAdOx1 nCov-19 vaccine by Oxford Astra Serum Institute of India and the Sputnik V from Russia’s Gamaleya Research Institute, to be marketed by Dr Reddy’s lab in India)

Vectors are viruses that have been modified to contain antigens from the target pathogen. The modified viruses act as delivery systems that display the antigens to our immune cells. Replicating viral vectors make extra copies of themselves in our body’s cells. Non-replicating viral vectors do not. Chimpanzee adenovirus is the vector used to deliver the corona virus antigen in the SII vaccine Covishield

c. Inactivated vaccine

(Covaxin by Bharat Biotech International Ltd (BBIL)

It consists of inactivated versions of the virus. These are detected by our immune cells but cannot cause illness.

2. How effective are these vaccines?

The Oxford Astra Serum Institute vaccine (ChAdOx1 nCov-19) has demonstrated efficacy of 70.4% against symptomatic COVID-19 and 100% efficacy against hospitalization due to severe COVID-19.

The Pfizer-BioNTech mRNA vaccine has been demonstrated to have 95% efficacy measured from 7 days after the 2nd dose across age, gender and ethnicity. The efficacy in above 65 years was 94%. The Sputnik vaccine has demonstrated 92% efficacy.

3. Who can be administered the vaccine?

The 4 vaccines mentioned have undergone immunogenicity, efficacy and safety trials in 18 Years and above and hence will be evaluated for use in adults under “Emergency Use Authorisation”. Trials are underway for age group 12-18 and in due course of time the vaccines may be allowed to be used in this age group.

4.  Will all the 4 vaccines be made available and will everyone have access to all the vaccines?

The Oxford Astra-Serum Institute vaccine (ChAdOx1 nCov-19) has applied for EUA and is likely to be made available soon. The BBIL vaccine is yet to complete the phase 3 trial and submit the trial results for EUA. Sputnik is being tested in India. Pfizer-BioNTech vaccine may be made available in private sector.

Frontline workers, elderly, individuals with co-morbidities and then other healthy adults will be vaccinated in order of priority. None of these vaccines are currently recommended for individuals below 18 years of age.

5. Does an individual who previously had COVID need the vaccine?

It is not very clear if a natural infection would protect an individual in the long run. The antibodies developed by the corona infected individual wane over time. In the absence of a direct correlate of protection in the form of antibody titres and considering the unmeasured or undetected cell mediated immunity, waned antibody levels may not mean loss of protection. However, given the huge number of doses required, individuals who have recovered from COVID-19 will be considered last for vaccination.

6. Can a pregnant lady take the vaccine?

As on today there is no data on safety in pregnant women. Pregnant women were excluded from the trials.

7. Can it be given to immunocompromised individuals?

Yes, the mRNA vaccine and inactivated vaccines are safe and even the adenovirus vector vaccine is safe as the vector is non-replicating.

2 doses of 0.5 ml 28 days apart for the Oxford Astra Serum vaccine and 2 doses 21 days apart for the Pfizer-BioNTech mRNA vaccine and the Sputnik vaccine

9. How long does it take for the vaccine to develop antibodies (protection)?

Usually it takes 2 weeks for the antibody response. The mRNA vaccine of Pfizer has demonstrated response as early as 10 days after the 1st dose

10. How long will the protection last and will there be a need of a repeat or booster dose?

There is no clear answer to this. The subjects in Oxford Astra Serum vaccine was evaluated for efficacy for up to 4 months after the 2nd dose. The antibodies may wane but protection would last long, and no booster will be needed. But it will be proved only with time.

11. Will there be any side effects of vaccines?

Apart from local reactions like pain and tenderness, and mild fever, there have not been any safety signals in the trials conducted. Two subjects enrolled in the Pfizer BioNTech vaccine trial in UK developed allergic (anaphylactic) reaction following which the UK government issued a warning against use of this vaccine of there is a past history of allergic reaction.

12. What are the cold chain requirements for these vaccines?

The Oxford Astra serum vaccine and Sputnik can be stored at 2-8 degrees. However, the Pfizer mRNA vaccines need to be stores at – 70 degrees. It can be kept at – 20 degrees for a week and on field retains viability for a day at 2-8 degrees

13. Can a diabetic take the vaccine?

Yes, in fact Diabetes has been established as a risk factor for severe disease and adverse outcome and all diabetics must get vaccinated on priority

14. Can it be administered with the Flu vaccine?


15. What happens if an individual takes only one dose?

The vaccine is recommended in a two dose schedule for the desired level of protection. However, the trials have shown reasonable protection even after one dose.

16. How long can the 2nd dose be delayed?

It is recommended to follow the interval of 21-28 days between the two doses. However, if the 2nd dose is not given at the recommended time interval, it should be given at the earliest opportunity.

Immunologically, the 2nd dose should elicit a good response by virtue of the memory induced by the 1st priming dose

17. Can it be administered to an individual who has received plasma, either as a treatment for COVID or other indication?

It’s very likely that the donor plasma may contain anti COVID-19 antibodies and may suppress the immune response to the vaccine. As said before those recovered from COVID-19 may not need the vaccine.

18. Can I roam free once I am vaccinated?


COVID is a new disease and we are still on a learning curve. No vaccine protects 100%. The vaccine is shown to be effective in prevention of symptomatic disease and severe disease needing hospitalization. However, its ability to protect the vaccine against infection (without causing disease, what is known as asymptomatic infection) is not certain. A vaccinated person may not develop disease but may get such infection and may also transmit it to others in contact. We will have to continue to practice wearing mask, observing physical distance and sanitizing hands to prevent transmission.

Once about 70% population has antibodies following the disease or post vaccination, the virus may not find a susceptible person to infect and will not spread, what is known as herd immunity.

Verified By Apollo Pulmonologist
The content is verified and reviewd by experienced practicing Pulmonologist to ensure that the information provided is current, accurate and above all, patient-focused

Quick Appointment

Most Popular


Overview Adrenalectomy is a surgery to remove one or both of your adrenal glands. The two...

Antinuclear Antibody Test

Our immune system develops antibodies or proteins that detect harmful pathogens, toxins, or infectious organisms and helps eliminate these pathogens, thereby preventing...

कोविड 19 की वैक्सीन लगने से पहले, लगने के बाद और लगने के समय क्या उम्मीद करें।

इंडिया में डी.जी.सी.आई ने कोरोना वायरस (कोविड-19) को रोकने के लिए दो वैक्सीन्स को मंजूरी दी है- कोवैक्सीन और कोविशील्ड।

Walking: A More Potent Exercise than We Think

Staying active and working out is not always stressful.  Walking is the most simplest way to work out, and you can do...