An article in the Scientific American asked some questions and gave some answers.

If you are eligible, should you have COVID vaccine?

Yes, if you are currently eligible to get a vaccine, you should have it.

In order to build herd immunity and slow the spread of disease, it is important to get as many people vaccinated as possible.

Should you get vaccinated if you have already had COVID?

Currently, the advice is that you should get vaccinated and this should be a minimum of 28 days following the onset of symptoms.

How does one interpret vaccine efficacy? What does 95% efficacy or 66% efficacy mean?

Vaccine efficacy refers to how well it performs in a carefully controlled trial, whereas effectiveness describes its performance in the real world.

There is a common mistake to interpret a 95% efficacy to mean you have a 5% chance of getting sick even if you get vaccinated.  This is not true at all. 

Efficacy is calculated based on trials that have an unvaccinated placebo control group, and at the end of the trial, they look at the number in the control group that ended up with symptomatic COVID to get the baseline infection rate. 

The Pfizer vaccine for instance had 95% efficacy in its clinical trial.  That number came from the fact that 162 people in the placebo group got symptomatic COVID and eight people in the vaccinated group did, that is 170 cases total, eight is approximately 5% of 170.  

That is essentially how efficacy is calculated.  Most COVID vaccine clinical trials have reported efficacy in preventing any symptomatic disease, not necessarily severe disease; early data for the latter however is promising. 

If you get the vaccine and still get infected, does the vaccine still make a difference? Will it prevent severe disease or death?

Yes.  From what has been seen with most of the current vaccines is that there are less severe symptoms and almost no hospitalisations and deaths in vaccinated people who become infected.

Several vaccine trials have observed a reduction in severe disease in the vaccinated subjects.  

With few expectations such as possibly the AstraZeneca vaccine in South Africa, the vaccines appear to reduce the risk of getting symptomatic COVID, but if one does get it, it is very likely to be a less severe case.

Do the vaccines protect against the new virus variants, including those first identified in the United Kingdom, South Africa and Brazil?

The data so far suggests that most of the vaccines do provide at least some protection against the new variants.

It has been seen from some of the clinical trial data and antibody neutralisation studies that vaccines designed against the original strains of the virus might not be quite as effective against certain new variants. Particularly against mutations found in the B1.351 variant that is now widespread in South Africa.  

Many of the new variants have changes in the spike protein, which the virus uses to infect cells, so it is a little bit different than what a vaccinated person’s body has seen before in the vaccine. 

Still, overall, the vaccines, which are authorised, are meeting efficacy targets and seem to give some protection against the new variants. 

The best way to prevent new variants from emerging is by getting lots of people vaccinated.  

The vaccine manufacturers are developing booster shots to offer additional protection if needed. 

What is the difference between mRNA and viral vector vaccines?

An mRNA vaccine – such as the ones made by Pfizer or Moderna – provide genetic instructions for making viral proteins in the form of a single stranded RNA, in a lipid coat, to your cells, without injecting any virus itself.

This has some exciting advantages because it can only contain those virus components that you want the immune system to recognise. 

It causes your own cells to mimic the way viral proteins are made when a cell is naturally infected with the virus.

It is remarkably good at inducing the same type of immune response that would occur in a natural infection.  

The downside, however, is that the mRNA needs to be kept very cold for it to be stable. 

Viral vector vaccines – such as those made by AstraZeneca or Johnson and Johnson, these are double-stranded DNA instead of RNA, but are still delivering genetic instructions to your cells.  They use a modified, safe virus to deliver the instructions for making viral proteins.

Is there a best vaccine?

Different vaccine designs are chosen because they have unique advantages, so there is not a best vaccine, but there might be a vaccine that is better for certain groups of people to take.

Both mRNA and viral vector vaccines instruct your cells to make pieces of the Coronavirus spike protein so that the next time your body encounters these proteins, it can mount an immune response. 

Efficacy numbers are derived from different clinical studies that were done in different settings, so instead of comparing those numbers, the thing to take away is that authorised vaccines generally work, they have efficacy.

Will the vaccine protect you from giving the virus to others?

It is thought that the answer is yes but as yet, we do not fully know.

There are two key goals of vaccines: 

  • To protect the individuals and to stop the spread of disease.
  • There are reasons to be hopeful based on what is known about viruses and there is some emerging data but it is still not known for sure if vaccines can reduce disease transmission. 

That is why it is still important to continue social distancing, wearing masks and following all guidelines to prevent the spread of disease even if one has been vaccinated. 

Will the vaccine’s effectiveness wear off over time?

It is possible that this could happen.

Vaccines often need booster doses to confer the best levels of protection. 

Some vaccines can protect someone for a lifetime, whereas others require a booster every few years.

It is important that the immune response is monitored over time in those who have been vaccinated so it will be known whether boosters are needed. 

Currently most of the available vaccines require two doses to be effective. 

Should one be worried about allergic reactions to the vaccine?

Allergic reactions can occur in response to any injected vaccine or drug, but they are in fact extremely rare.

The vaccine should always be administered in settings where healthcare providers can treat any allergic reactions that develop unexpectedly. 

On the whole, one does not need to be concerned about the vaccines if there is any history of food allergy or latex allergies.

Most people do not need to worry about an allergic reaction.  For those with a history of severe allergic reactions or allergies to vaccine ingredients, it is best that this is discussed with your doctor.

What side effects can be experienced and what are normal?

The common side effects are what one would expect for other vaccines such as fatigue, headache, fever, particularly after the second dose and acute pain at the injection site, which can feel warm to the touch and swollen.

All of these symptoms are signs of immune reaction.  These reactions are very common and often indicate that the immune system is working hard to recognise the vaccine and remember the new virus for the next time.

How can it be ensured that one is getting a legitimate authorised vaccine?

This is why in most countries the vaccine is only being distributed through government sources and is not available privately.

It is important to make sure that vaccines are given under the supervision of a licensed medical practitioner.


Yours sincerely,

Harley Street doctor covid vaccine

Dr Paul Ettlinger

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