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COVID-19 vaccine efficacy and effectiveness

Eradication of smallpox, near elimination of poliomyelitis and neonatal tetanus and substantial reduction in impact of measles are ranked amongst the greatest achievements of humankind ever. These triumphs are the outcomes of the availability and concerted use of potent, safe and affordable specific vaccines. In addition, protecting against 20 infectious diseases, the vaccines prevent 2-3 million deaths annually.

Apart from natural infections, vaccines are considered as the safest and cost-effective intervention to induce protection against COVID-19.

COVID-19 vaccines have shown up to 95 percent efficacy 1 in preventing clinical cases and up to 100 percent efficacy 2 in preventing severe disease or admission to hospital in settings with pre-existing variants.

The COVID-19 vaccines are expected to provide at least some protection against new virus variants and are effective at preventing serious illness and death. That’s because these vaccines create a broad immune response, and any virus changes or mutations should not make vaccines completely ineffective. If any of these vaccines become less effective against one or more variants, it will be possible to change the composition of the vaccines to protect against these variants. Data continues to be collected and analyzed on new variants of the COVID-19 virus.

To expedite regulatory approval, on Oct 6, 2020, the US Food and Drug Administration (FDA) published a guidance document outlining its receptiveness to issuing an emergency use authorization to a candidate vaccine on the basis of an interim analysis of a clinical endpoint from a phase 3 efficacy study. In this document, they state,“To ensure that a widely deployed COVID-19 vaccine is effective, the primary efficacy endpoint point estimate for a placebo-controlled efficacy trial should be at least 50 percent, and the statistical success criterion should be that the lower bound of the appropriately alpha-adjusted confidence interval around the primary efficacy endpoint point estimate is >30 percent.”

Vaccines often suffer from underinvestment, but that has not been the case in this pandemic. As of Feb 3, 2021, there were 289 experimental COVID-19 vaccines in development, 66 of which were in different phases of clinical testing, including 20 in phase 3. Only five of these 66 vaccines—those developed by AstraZeneca in partnership with Oxford University, BioNTech in partnership with Pfizer, Gamaleya, Moderna, and Sinopharm in partnership with the Beijing Institute—have been authorised by stringent regulatory authorities (as per WHO criteria of such authorities) or WHO. Another five—from China, India, Kazakhstan, and Russia—have received approval or been authorized for emergency use by other regulatory agencies; some of the organizations developing these vaccines have submitted documentation to WHO for emergency use listing or prequalification, but these submissions are still under review. Ten additional vaccines from Novavax and Johnson & Johnson are expected to be authorized on the basis of positive interim phase 3 results. Several vaccines have shown high levels of efficacy (ie, more than 70%) in clinical trials, although not all developers have published their results; most of the authorized vaccines have been shown to provide strong protection against hospitalizations and deaths due to COVID-19.

Several different types of potential vaccines for COVID-19 are in development, including:

  • Inactivated or weakened virus vaccines, which use a form of the virus that has been inactivated or weakened so it doesn’t cause disease, but still generates an immune response.
  • Protein-based vaccines, which use harmless fragments of proteins or protein shells that mimic the COVID-19 virus to safely generate an immune response.
  • Viral vector vaccines, which use a safe virus that cannot cause disease but serves as a platform to produce coronavirus proteins to generate an immune response.
  • RNA and DNA vaccines, a cutting-edge approach that uses genetically engineered RNA or DNA to generate a protein that itself safely prompts an immune response.

The COVID-19 vaccines produce protection against the disease, as a result of developing an immune response to the SARS-Cov-2 virus. Developing immunity through vaccination means there is a reduced risk of developing the illness and its consequences. This immunity helps you fight the virus if exposed. Getting vaccinated may also protect people around you, because if you are protected from getting infected and from disease, you are less likely to infect someone else. This is particularly important to protect people at increased risk for severe illness from COVID-19, such as healthcare providers, older or elderly adults, and people with other medical conditions.

The COVID-19 vaccine will not cause a positive test result for a COVID-19 PCR or antigen laboratory test. This is because the tests check for active disease and not whether an individual is immune or not. However, because the COVID-19 vaccine prompts an immune response, it may be possible to test positive in an antibody (serology) test that measures COVID-19 immunity in an individual.

Even if anyone already had COVID-19, they should be vaccinated when it is offered. The protection that someone gains from having COVID-19 will vary from person to person, and we also do not know how long natural immunity might last.

Two vaccines that have been granted emergency use authorization by the Central Drugs Standard Control Organization (CDSCO) in India are Covishield® and Covaxin®.

Covishield® vaccine, manufactured by Serum Institute of India, is a viral vector-based technology which is also used to manufacture Ebola vaccine.

Covaxin® vaccine, manufactured by Bharat Biotech, is a whole-virion inactivated coronavirus vaccine which is also used to manufacture vaccines like influenza, rabies, and hepatitis- A.

Both vaccines need to be stored and transported at +2 to +8° Celsius. The cold chain for both vaccines is maintained through active and passive cold chain equipment available at cold chain points across India