All such questionsare in the mind of millions.Nationally acclaimed,Dr. Raja Dhar, Head of the Department Pulmonology, CK Birla Hospitals- CMRI and BMB Heart Research Centre, Kolkata gives a detailed account on vaccines. He has seen more than thousand Covid patients during the time of Covid.Dr. Raja Dhar is a proficient clinician in all disciplines of Respiratory Medicine which includes treating patients with COVID, airways disease, pulmonary fibrosis, pulmonary hypertension, transplant, lung cancer, sleep medicine, lung infections including TB, and respiratory emergencies. His forte is Interventional Pulmonology including electrocautery, APC, cryotherapy, stent placements and Medical Thoracoscopy.
Talking all about the vaccines, Dr. Dhar explains, “There’s a lot of concern among the layman and also in the medicalfraternity as to whether one should take the covid vaccine or not.The unambiguous answer to this question is that we should all receive the covid vaccines”.
One of the biggest achievements in the last year or even for longer has been the time span over which a covid vaccine has been developed. Normally, it would take about 10 years to develop a vaccine of a similar ilk. However, it’s the hard work of the scientists in India and globally which is resulted in a vaccine being developed in such a short period of time. Although, no one can be forced to take the vaccine with or without their consent.The healthworkers, the high-risk population and most people should take the vaccine as soon as it is made available for them. All drugs can have side effects, all injections can cause allergic reactions. However, there is no added risk of taking a vaccine in fact, vaccines are generally being thought to be safer, an on a balance taking a vaccine saves far more lives as compares to the morbidity and mortality that one might anticipate from the vaccine.
We should dispel rumours that the vaccine contains microchips; that it may cause side effects; that it would be ineffective against Covid. Our best bet against the virus is by getting vaccinated. This does not mean that we do away with practices which have become the new normal; like wearing masks, sanitizing hands, maintaining physical distance etc. However, the vaccine definitely gives us added protection over and above what is achieved by the health control measures just described.
Vaccines till date have come in different categories. They can be live attenuated vaccines; they can be killed inactivated vaccines or vaccines containing antigenic components to induce immune response in unprotected individuals.
Vaccines that contain live organisms are called live attenuated vaccines. The first step in preparing a live vaccine is to try and neutralize their pathogenicity but preserve their antigenic properties. They can be given by various routes; the oral route, the intra-muscular, the sub-cutaneous or the intradermal routes. The TB vaccine, the MMR vaccine and the oral polio vaccine are all examples of the live attenuated vaccine. The live attenuated vaccines are contra-indicated in immune-compromised individuals.
The next class of vaccines are the killed or inactivated vaccines. These include the influenza vaccine for intramuscular use; the inactivated polio vaccine; the whooping cough vaccine. These vaccines contain a portion of the microbe or its toxin without their pathogenic effects. The other examples are the pneumo-coccal vaccine, the hepatitis B vaccine, the tetanus toxoid etc. The inactivated microbes or their components act as antigens that induce antibody production in the body. The antibody response here is more long-lasting, especially for blood borne viruses, such as Hepatitis B; and shorter lasting for respiratory viruses like influenza. The short-lasting immunity in influenza is also due to the mutations that occur in the latter. Cell mediated immune response last for a longer period than humoral immune response. This is not triggered by the killed or inactivated vaccines.
Covaxin is an inactivated vaccine against SARS-COV 2, the causative agent of COVID-19, for which there is an ongoing Phase-3 trial. There has been an emergency authorization from the Government of India even while the Phase 3 trials are on. Covaxin is manufactured by Bharat Biotech which is an organization famous for production of vaccines. It contains an inactivated whole virion, the NIV 2020 – 770 strains of SARS COV 2. Since it contains all the proteins of the virus; spike protein, nucleo-protein etc., it is likely to give protection against the SARS COV 2 mutants as well. Two doses need to be taken and they should be split apart by 4 to 6 weeks. The second does helps in augmenting the immune response.
The DNA based vaccines are relatively new, technologically. There are numerous examples. The hepatitis B, hepatitis C, human papilloma virus, malaria etc., all of which are still undergoing clinical trials. The DNA vaccines available against COVID are the Sputnik vaccine and the Covishield. The Covishield, which is available in India currently, is the Oxford vaccine (AstraZeneca) which has completed all phases of its trial and is manufactured in India by the Serum Institute in Pune. In these vaccines, a chimpanzee adenovirus is used as the vector. Adenoviruses are the DNA copy of the S-gene of SARS COV 2 which encodes for spike protein and is inserted in its place. After the vaccine is injected into the body by IM injection, adenovirus vector binds the target receptor on respiratory and gastrointestinal epithelium and on the cells in the eye. The vector inserts its genome into the host cell. The adenovirus genome does not integrate into the host cell genome, but SARS COV 2 gene copy does and instructs the host cell ribosome to synthesize MRNA that encodes SARS COV 2 spike protein. This induces T cell immunity and antibody production which gets improved / augmented after the second dose given after 4 to 6 weeks. It should be kept in mind that future vaccination for another infection using the same adenovirus vector will not work in individuals vaccinated with the DNA vaccine for SARS COV 2.
The next category, a completely new category of vaccines, is the MRNA, or Messenger RNA, Covid vaccines and these include the Pfizer and the Moderna vaccines. Bio-technologically, these vaccines are a new entity for us. Numerous copies of MRNA, encoding SARS COV 2 spike protein synthesis, are inserted into phospholipid capsules and injected by IM route. The MRNA enters human cells normally affected by SARS COV 2 and directly induces spike protein synthesis in these host cells. Thus, such vaccines induce immunity, both cellular and humoral, faster than the DNA counterparts. Two doses, 4 to 6 weeks apart are needed but RNA, unlike DNA or protein, needs to be preserved at -70 degrees Celsius for long term storage as it degrades at higher temperature. DNA or antigen-based vaccines are stable for longer periods at 2 to 8 degrees Celsius. There are some reports of increased adverse events with the Covid MRNA vaccine compared with the DNA or inactivated vaccines. Adverse events usually occur more due to inactive ingredients than the active ingredients of the vaccine. Several ingredients are added as stabilizers or adjuvants to the vaccine.These include aluminium compounds, alcohol,gelatines, sorbitol, albumin etc. However, such adverse effects are rare and mild.
An apprehension that is doing the rounds is whether the vaccine will cover the mutant strains. Most of the mutations are occurring in the S-gene that encodes spike protein. However, the mutations are involving small number of nucleotides. Hence the immune response which develops in the body following vaccinations will hopefully cover the mutants. Inactivated vaccines including all viral proteins will confer better humoral immunity against mutants but they do not induce long lasting cellular immunity, unlike the nucleic acid based vaccines.
The arrival of vaccines is beginning to have an impact on everyday life, with millions of newly inoculated eagerly anticipating a return to long-postponed activities and visits with sorely missed relatives and friends. Dr. Dhar warns that vaccinations are not a “pass,” the recently inoculated are engaged in a new round of complicated risk-benefit assessments. The safety of the vaccines has been proved beyond doubt. Even if it gives 60% protection, it is good for an individual to break the chain of transmission.