Coronavirus disease (COVID-19) is caused by infection with an RNA (ribonucleic acid) virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus strain which is a newly discovered coronavirus.
Most people who fall sick with COVID-19 will experience mild to moderate symptoms and recover without special treatment.
Clinical symptoms
COVID-19 is an emerging disease and complications can be severe and fatal, particularly for those in risk groups. Asymptomatic infection has been reported but those who do develop symptoms report a range of symptoms which include fever, new and continuous cough, shortness of breath, fatigue, loss of appetite, loss of smell and loss of taste. Other symptoms include: myalgia, sore throat, headache, nasal congestion, diarrhoea, nausea and vomiting.
Transmission: How it spreads?
SARS-CoV-2 virus is primarily transmitted through droplets generated when an infected person coughs, sneezes or exhales. These droplets are too heavy to hang in the air, and quickly fall on floors or surfaces. You can be infected by breathing in the virus if you are within close proximity of someone who has COVID-19 or by touching a contaminated surface and then your eyes, nose or mouth.
The body’s natural response: How the normal immune system of our body functions?
Germs are all around us, both in our environment and in our bodies.
When a person is susceptible and they encounter a harmful organism, it can lead to disease and death.
When a pathogen (disease-causing agent) does infect the body, our body’s defences, called the immune system, are triggered and the pathogen is attacked and destroyed or overcome.
A pathogen (disease-causing agent) could be a bacterium, virus, parasite or fungus that can cause disease within the body.
Each pathogen is made up of several subparts/subunits, usually unique to that specific pathogen and the disease it causes
. The subpart/subunit of a pathogen that causes the formation of antibodies is called an antigen.
An antibody is a protective protein produced by the body’s immune system in response to the pathogen’s antigen, and is an important part of the immune system. You can consider antibodies as the soldiers in your body’s defence system.
Each antibody or soldier, in our system is trained to recognise one specific antigen.
We have thousands of different antibodies in our bodies.
When the human body is exposed to an antigen for the first time, it takes time for the immune system to respond and produce antibodies specific to that antigen.
In the meantime, the person is susceptible to becoming ill.
Once the antigen-specific antibodies are produced, they work with the rest of the immune system to destroy the pathogen and stop the disease.
Antibodies to one pathogen generally don’t protect against another pathogen except when two pathogens are very similar to each other.
Once the body produces antibodies in its primary response to an antigen for the first time, it also creates antibody-producing memory cells, which remain alive even after the pathogen is defeated by the antibodies.
If the body is exposed to the same pathogen more than once, the antibody response is much faster and more effective than the first time around because the memory cells are at the ready to pump out antibodies against that antigen.
This means that if the person is exposed to the dangerous pathogen in the future, their immune system will be able to respond immediately, protecting against disease.
What is a vaccine?
A vaccine is a type of medicine that trains the body’s immune system so that it can fight a disease it has not come into contact with before. Vaccines are designed to prevent disease, rather than treat a disease once you have caught it.
What does a vaccine contain?
Vaccines contain weakened or inactive/killed parts of a particular pathogen/organism (antigen) that triggers an immune response within our body. Newer vaccines contain the blueprint for producing antigens rather than the antigen itself. This weakened version will not cause disease in the person receiving the vaccine, but it will prompt their immune system to respond much as it would have on its first reaction to the actual pathogen. How vaccine prevents COVID-19? The coronavirus that causes COVID-19 has spikes of protein on each viral particle. These spike proteins allow the virus to attach to cells and cause disease.
The vaccines help the body to “recognise” these spike proteins as foreign and fight the coronavirus that has them. The vaccine will protect a person who receives it by lowering their chances of getting COVID-19 if they encounter the coronavirus.
Why two or more doses?
In general, some vaccines require multiple doses, given weeks or months apart. This is sometimes needed to allow for the production of long-lived antibodies and development of memory cells. In this way, the body is trained to fight the specific disease-causing organism (pathogen), building up memory of the pathogen so as to rapidly fight it if and when exposed in the future.
Why are there different types of COVID-19 vaccines?
Having a range of COVID-19 vaccines available for people to use around the worldwill be essential to bringing the pandemic
under control. We need a range of COVID-19 vaccines to work for a diverse range of people – including older people and those with underlying health conditions As of December 2020, there are over 200 vaccine candidates for COVID-19 being developed.
Of these, 52 candidate vaccines are in human trials. There are several others currently in phase I/II, which will enter phase III in the coming months. Of the vaccines that do make it to clinical trials, just one in five is successful. Having lots of different vaccines in development increases the chances that there will be one or more successful vaccines that will be shown to be safe and efficacious for the intended prioritised populations.
What is the principle behind the different types of COVID-19 vaccines?
There are three main approaches to designing a vaccine. Their differences lie in whether they use a whole virus; just the parts of the virus (subunit) that triggers the immune system; or just the genetic material that provides the instructions for making specifi proteins and not the whole virus.
- The whole microbe approach includes the following types of vaccine: inactivated vaccine, live-attenuated vaccine and viral
vector vaccine; - The subunit approach uses specific parts of the virus that the immune system needs to recognise;
- The genetic approach uses a section of genetic material, the ribonucleic acid (RNA) that provides the instructions for
specific proteins, not the whole microbe.
Most COVID-19 vaccines require two doses. This includes the Oxford/AstraZeneca vaccine, the BioNTech/Pfi zer vaccine and
Novavax vaccine.
Whether you will need additional booster doses, such as an annual booster, for COVID-19 vaccines is still being determined by
ongoing clinical trials.
The first dose of COVID-19 vaccine should give you good protection from coronavirus.
But, you need to have the two doses of the vaccine to give you longer lasting protection.
The AZD1222 vaccine (Oxford/AstraZeneca vaccine) against COVID-19 has an efficacy of 63.09 per cent against symptomatic
SARS-CoV-2 infection.
Longer dose intervals within the 8 to 12 weeks range are associated with greater vaccine efficacy.
The BioNTech/Pfi zer vaccine showed protection seven days after the second dose; 95 per cent efficacy was observed.
A vaccine that is 95 per cent effective means that about one out of 20 people who get it may not have protection from getting
the illness.
The SARS-CoV-2 vaccine produced by the US biotechnology company Novavax is 95.6 per cent effective against the original variant of SARS-CoV-2 but also provides protection against the newer variants, the UK/ Kent variant B.1.1.7 (85.6 per cent) and the South African variant B.1.351 (60 per cent), preliminary data from clinical trials show.
However, another study shows that the vaccine is less than 50 per cent effective against a worrying lineage called 501Y.V2,
which was detected in South Africa and is spreading around the world.
The NVX-CoV2373 vaccine can be stored at 2°C to 8°C and has been found to be safe.
The Moderna mRNA-1273 vaccine has been shown to have an efficacy of approximately 92 per cent in protecting against COVID- 19, starting 14 days after the first dose.
Two doses are recommended with 28 days apart.
If necessary, the interval between the doses may be extended to 42 days.
Recently, the US FDA gave emergency authorization to Johnson & Johnson’s single dose COVID-19 vaccine.
The vaccine can be stored in a refrigerator instead of a freezer.
The Johnson & Johnson vaccine seems to be very safe, with only a few side effects such as pain and redness at the site of injection, fatigue and headaches.
There was also one reported case of anaphylaxis (allergic reaction) related to the vaccine.
In clinical trials, the Johnson & Johnson vaccine appears to be 66 per cent effective at preventing moderate to severe cases of COVID-19 28 days after vaccination.
It may take time for everyone who wants a COVID-19 vaccination to get one.
There is a chance you might still get or spread coronavirus even if you have the vaccine.
This means it is important to continue to follow social distancing guidance, to wear facemask especially in places where it is practice handwashing.
It is not yet known how long the protection afforded by a COVID-19 vaccine will last. This is being evaluated in ongoing research.
Can pregnant women receive COVID-19 vaccine?
Although the available data do not indicate any safety concern or harm to pregnancy, there is insufficient evidence to recommend the routine use of COVID-19 vaccine during pregnancy.
However, the joint committee on vaccinization and immunisation (JCVI, UK) has advised that, for women who are offered COVID-19 vaccine, vaccination in pregnancy should be considered where the risk of exposure to SARSCoV-2 infection is high and cannot be avoided, or where the woman has underlying conditions that put them at very high risk of serious complications of COVID- 19.
In these circumstances, clinicians should discuss the risks and benefits of vaccination with the woman, who should be told about the absence of safety data for the vaccine in pregnancy.
JCVI does not advise routine pregnancy testing before receipt of a COVID-19 vaccine. Those who are trying to become pregnant do not need to avoid pregnancy after vaccination.
Can breastfeeding mothers receive COVID-19 vaccine?
There is no known risk associated withgiving non-live vaccines whilst breastfeeding.
JCVI advises that breastfeeding women
may be offered vaccination with the COVID-19 mRNA Vaccine BNT162b2 or COVID-19 Vaccine AstraZeneca.
The developmental and health benefits of breastfeeding should be considered along with the woman’s clinical need for immunisation against COVID-19, and the woman should be informed about the absence of safety data for the vaccine in breastfeeding women.
What are the possible adverse reactions following vaccination?
Local reactions at the injection site were found to be fairly common after vaccination with the COVID-19 mRNA Vaccine BNT162b2 during clinical trials.
More than 80 per cent of trial participants reported pain at the injection site.
This occurred within seven days after the injection and resolved after a few days.
In clinical trials, the most frequently reported systemic reactions in participants were tiredness (by more than 60 per cent of participants), headache (> 50 per cent), muscle aches (> 30 per cent), chills (> 30 per cent), joint pain (> 20 per cent) and a raised temperature (pyrexia) (> 10 per cent).
These symptoms were usually mild or moderate in intensity and resolved within a few days after vaccination.
If required, symptomatic treatment with analgesic and/or anti-pyretic medicinal products (eg paracetamol containing products) may be used.
More than 60 per cent of COVID-19 Vaccine AstraZeneca trial participants reported tenderness at the injection site with redness, swelling, itching, warmth and pain at the injection site also being reported.
The most frequently reported systemic reactions were headache and tiredness (by more than 50 per cent of participants); muscle aches and feeling generally unwell (>40 per cent); raised temperature (pyrexia) and chills (>30 per cent) and joint pain and nausea (>20 per cent).
The majority of adverse events reported during the clinical trials of the COVID-19 Vaccine AstraZeneca were mild to moderate and short-lasting, usually resolving within a few days of vaccination.
When compared with the first dose, adverse reactions reported after the second dose were milder and reported less frequently.
Prophylactic use of paracetamol was found not to affect the immune response to this vaccine.
What is herd immunity and does it give protection against COVID-19 infection?
Herd immunity (or community immunity) occurs when a high percentage of the community is immune to a disease (through vaccination and/or prior illness), making the spread of this disease from person to person unlikely.
Even individuals not vaccinated (such as the immunocompromised) are offered some protection because the disease has little opportunity to spread within the community.
When someone is vaccinated, they are very likely to be protected against the targeted
disease. But not everyone can be vaccinated.
People with underlying health conditions that weaken their immune systems (such as cancer or HIV) or who have severe allergies to some vaccinecomponents may not be able to get vaccinated with certain vaccines.
These people can still be protected if they live in and amongst others who are vaccinated.
When a lot of people in a community are vaccinated, the pathogen has a hard time circulating because most of the people it encounters are immune.
So the more that others are vaccinated, the less likely people who are unable to be protected by vaccines are at risk of even being
exposed to the harmful pathogens. This is called herd immunity.
This is especially important for those people who not only can’t be vaccinated but may be more susceptible to the diseases we vaccinate against.
No single vaccine provides 100 per cent protection, and herd immunity does not provide full protection to those who cannot safely be vaccinated.
But with herd immunity, these people will have substantial protection, thanks to those around them being vaccinated.
Conclusion
Vaccines are a safe way of producing an immune response in the body without causing illness.
Vaccinating not only protects yourself, but also protects those in the community who are unable to be vaccinated.
If you have already had COVID-19 and recovered, you may have some natural immunity to contracting the disease again.
However, because this virus is new, it’s not clear how long natural immunity might last. Even if you have had COVID-19, you should still have the vaccine to help protect against getting COVID-19 again or passing it on to someone else.
It is not yet known how long the protection afforded by a COVID-19 vaccine will last.
There is a chance you might still get or spread coronavirus even if you have the vaccine.
Therefore, follow physical (social) distancing, wearing facemask especially in crowded places, handwashing, respiratory and cough hygiene, avoiding crowds and ensuring good ventilation.
- Dr Sivaselvam Sivakumar is the headof Lab and Transfusion Services at Oceania Hospitals Pte Ltd. The views expressed are the author’s and do not reflect the views of this newspaper
