This is for those who question why scientists have made Covid19 vaccine in less that a year but they have been struggling to get us vaccines for HIV and cancer.

1. HIV - first HIV binds to the host receptors triggering entry into the cells to synthesize double stranded DNA. This viral DNA get integrated with the host genome. Once the viral DNA is integrated, infection of HIV is permanent.

The integration of viral DNA with host genetic material is the reason we still do not have a vaccine. Scientists do not know how to remove viral DNA from host genome without manipulating host genome.

2. Cancer - there are many types of cancers. Even worse, cancer does not target one type of organ. And each organ respond differently. There is no way scientists will make one vaccine for all these type of cancers. One-size- fits- all approach does not work with cancer.

3.Coronaviruses have been there for years. In general, viruses are not complicated. It's a single cell, with envelop, capsid and viral genome. Covid19 vaccine is targeting envelop proteins.

Now, the concern with vaccines and the reason they undergo trials is to test whether the vaccine will induce immunity with minimal side effects or not.