Experts Explain: How do vaccines work, and do they help? - The Indian Express

Evidence shows that incidence of an infectious disease goes down rapidly following the deployment of vaccines against it; several human diseases are now vaccine preventable.

He is best known for his efforts towards developing a vaccine for malaria.

Phase 3: involves thousands of volunteers in a blinded manner to compare those who get the vaccine to those who don’t (they get a placebo or dummy) to re-confirm safety, serious side-effects if any, and most importantly, whether the vaccine is efficacious in preventing infection and/or disease.

In the present case, vaccines for Covid-19 have been readied within a year.

There are currently 68 Covid-19 vaccines in human clinical trials, of which 20 have reached phase 3 testing, eight have received limited or emergency use approval, and two have been approved for full use.

Another crucial reason was the use of every available vaccine platform to produce a Covid-19 vaccine, including those that had so far not produced a vaccine for humans.

The vaccines made by Pfizer/BioNTech and Moderna both directly deliver an mRNA fragment into human cells to produce the viral Spike protein which raises anti-viral immunity.

An experimental adenovirus-based Ebola vaccine was used to vaccinate about 60,000 people in West Africa during the 2014-16 Ebola outbreak.

Researchers at Oxford University in the United Kingdom had been using the chimpanzee adenovirus platform for several experimental vaccines, which was quickly repurposed to develop a Covid-19 vaccine.

Finally, vaccines based on inactivated viruses is a time-tested method, which has been used in the ICMR/Bharat Biotech vaccine as also in at least three vaccines from China.

Viral vector vaccines are more stable (2 to 8 deg C storage), but the same vector cannot be used for another disease in the same person because anti-vector immunity will make it ineffective.

Though inactivated viral vaccines are generally safe, similar vaccines against respiratory syncytial virus and measles were withdrawn as they exacerbated the disease.

It allows vaccines to be used in an emergency in groups that are at high risk of infection, morbidity, and mortality.

Any cases of vaccine failure — such as those who get the disease even after getting fully vaccinated — should be investigated for what viral variants they harbour, and if these can be neutralized by the sera of recovered patients and vaccinated persons.