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How long does it take for the Covid-19 vaccines to become effective?

Covid-19 has kept the world on its toes ever since its outbreak. It has been more than a year of uncertainty but thanks to the efforts of the healthcare fraternity, it seems we are heading towards a better future. Covid-19 vaccines from different manufactures are available indifferent parts of the world. So far, vaccines from Pfizer, Covishield, Sputnik V, Sinovac, and Moderna are being given to healthcare workers and vulnerable population groups in many countries.

In Bangladesh, the DGHS (Directorate General of Health Services) has vaccinnated people with Covishield  vaccine from the Oxford/AstraZeneca and manufactured by the Serum Institute of India (SII). It has also approved Russian Sputnik V vaccine.

Constituents of the vaccines

Covishield is made from a weakened version of a common cold virus/ adenovirus from chimpanzees. Sputnik V is based on human adenovirus platform, a tried and extensively tested one that was used to successfully fight Ebola in the past. The AstraZeneca vaccine on the contrary is based on chimpanzee adenovirus. Covaxin is developed using Whole-Virion Inactivated Vero Cell derived platform technology.



Vaccine efficacy is defined to measure whether the vaccine is able to prevent the disease significantly or not, and if so, to what extent. Though no vaccine would be 100 per cent effective, clearly, the higher the value of vaccine efficacy, the better is the performance of the potential vaccine.

Oxford-AstraZeneca vaccine and Sinovac vaccine are a lot more useful to developing countries which might not be able to store large amounts of vaccine at such low temperatures.


While Oxford-AstraZeneca vaccine Covishield continue to provide protection against the coronavirus, there are vaccines globally such as Johnson and Johnson, Sputnik V to name a few that have proven extremely efficient during the third phase of clinical trials.

While Sinopharm stands at 79.3 per cent, Johnson and Johnson at 85 per cent and Sinovac at 50.4 per cent. Sputnik V has proved to be 91.6 per cent effective, while also offering full protection from severe cases or hospitalisation due to Covid-19.

Sputnik V

Sputnik V is also an adenovirus vaccine. It is one of the Covid-19 vaccines that has an efficacy rate of over 92 per cent. So far, Sputnik V is approved for use in 60 countries and is positioned as the second among Covid-19 vaccines worldwide in terms of approvals issued by various regulators.


CoronaVac, also known as the Sinovac COVID-19 vaccine, is an inactivated virus COVID-19 vaccine developed by the Chinese company Sinovac Biotech. The vaccine was 79.34% effective in preventing people from developing the disease based on interim data. It has been approved in several countries including China, Pakistan and the UAE.

One of Sinovac’s main advantages is that it can be stored in a standard refrigerator at 2-8 degrees Celsius, like the Oxford vaccine, which is made from a genetically engineered virus that causes the common cold in chimpanzees.


Pfizer-BioNTech is approximately 52.4 per cent effective after the first dose and becomes 92 per cent effective 14-21 days later, according to experts. One week after the second dose, the Pfizer-BioNTech vaccine will be 95 per cent effective in preventing COVID-19. Pfizer’s vaccine needs to be stored at -70C.


Moderna offers an 80 per cent efficacy rate after the first dose, and later a 92 per cent efficacy rate 14 days later. Two weeks after the second dose is administered, the vaccine will be 94 per cent effective in preventing COVID-19. Moderna’s vaccine needs to be stored at -20C.


For AstraZeneca, the vaccine will be 76 per cent effective after 22-90 days of the first dose. With an increased interval between the first and second dose, the effectiveness of AstraZeneca actually increases.

The second dose is nearly 63 per cent effective in preventing COVID-19 two weeks after the dose is administered, however, when the second dose is taken 12 weeks or more after the first dose, the vaccine becomes 82 per cent effective in preventing the virus, with immunity building over time.

Johnson & Johnson

Johnson & Johnson vaccine is 66 per cent effective in preventing COVID-19 two weeks after the vaccine is administered, and immunity will develop over time.

Lifelong protection from Covid-19


Various vaccines that have been developed to counter SARS CoV 2 have been designed keeping its various variants in mind but there is also a group of clinicians and virologists who believe that those once exposed to the virus may have lasting immunity against it and may not need vaccination. The researchers, on the other hand, have stressed that mutated forms of SARS-CoV-2 may be able to reinfect people who have recovered from an earlier infection.

A vaccine has some characteristics of the virus, which alerts the body to produce an anti-body so that if the real virus attacks it can protect the body. It is yet to be established that a vaccine can provide life-long immunity to a person. The benefit of the vaccine is that it will provide training to the body and will prepare it to fight against Covid-19. It depends on the individual immune system how good it gets trained with the help of the vaccine. The duration of anti-body might also vary from vaccine to vaccine as some vaccine might give longer protection compared to others.

The immune systems of more than 95 per cent of people who recovered from Covid-19 had durable memories of the virus up to eight months after infection. The results provide hope that people receiving SARS-CoV-2 vaccines will develop similar lasting immune memories after vaccination.

However, let’s not forget that vaccine cannot be the only solution in controlling the virus. This also needs to be complemented with Covid-appropriate behaviour (handwash, hygiene, physical distancing and mask).

With several promising vaccine candidates, some approved and a few under review, the next question in the search for an ideal vaccine will remain its long-standing immunity.