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From answering your questions about the Covid-19 vaccines we've seen some questions being asked a lot. 

To help you, we've grouped the answers to some of your frequently asked questions by theme in the sections below.

Please note: The data provided on this page is correct as of 5 April 2022.


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Should pregnant women receive the vaccination? What's the risk of vaccination versus Covid-19 infection in pregnancy?

We would recommend that all unvaccinated pregnant women receive the Covid-19 vaccination.

In general, there has been no evidence of any harm from the vaccines in pregnant women. The risk of harm from the Covid-19 virus itself is much greater, both in pregnant women and the unborn child.

As there are a lot of Covid-19 cases around at present, the potential relative risks of getting vaccinated during your first trimester, compared with later are trumped, by the greater risk of catching Covid-19.

Information available from “The Green Book”, published by the government, provides the latest information on vaccines and vaccination procedures in the UK.

Women’s health and fertility

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There have been reports of period irregularities following Covid-19 vaccination. Is there a risk of infertility?

This has been looked at by the Medicines and Healthcare products Regulatory Agency (MHRA) which is the national regulator for medicines in the UK.

There have been reports of period irregularities which have lasted for a short space time. As period irregularities are very common, there is no suggestion that this is above the level of normal variation.

There has been no evidence that fertility has been affected.

Risk of transmission with vaccination

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I understand that vaccination reduces the risk of severe Covid-19 infection, but is there any evidence that vaccination reduces the risk of transmission?

 There has not been a large amount of research around being infected with the SARS-CoV-2 virus and being able to transmit the virus, but not having the disease Covid-19 yourself.

If you are vaccinated you can be still be exposed to SARS-CoV-2 and be infected, but the levels of infection will be controlled by your immune system and you may not become ill. By effectively controlling the virus, preventing it from multiplying out of control, this will also reduce your potential for transmitting to others.

Vaccination after having Covid-19

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Do I need to get the vaccination after having Covid-19?

We would encourage you to get vaccinated even if you have had Covid-19 infection in the past.

This is for multiple reasons. Firstly, infection does give you protection against getting ill again, but only for a relatively short time, compared with other vaccines. A study done at St. George’s last year, showed that people who caught Covid-19 in the first wave of the pandemic were protected for about 5 to 6 months before we started seeing re-infections. 

Secondly, this protection may be less if you were ill with one variant, but encounter a new variant (like Omicron).

Will Covid-19 vaccinations become annual vaccinations, like the flu?

There has been much discussion about Covid-19 vaccines becoming the "new flu vaccine".

It’s difficult to say what will happen, but St George's Professor Julian Ma believes the spread and range of Covid-19 seems different than flu, so we could see regular boosters or modified vaccines becoming a regular thing. However, more of the population will need to be covered compared to the flu. It’s also not yet clear how frequent Covid-19 boosters might need to be.

How long do I need to wait after having Covid-19 before I can receive my vaccination?

Current advice from the NHS is that you should wait at least 28 days following Covid-19 infection before receiving a vaccination. 

Vaccine side effects and safety

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What are the common side effects from vaccination?

Most commonly a moderate reaction can occur after any vaccination (e.g. Mild fatigue, a sore arm and sometimes flu-like symptoms).

Severe reactions are very rare but do happen; usually they happen in the first 2 weeks; either immediately like an allergic reaction or around 11 days to 2 weeks.  

What are the significant side effects of vaccination, including blood clots and myocarditis?

Recent work involving 30 million NHS records showed that for every 10 million people the risk of getting a blood clot was:

  1. 66 people out of 10 million who had received the Astra Zeneca vaccine. (Pfizer is safer; and these numbers are lower than many other vaccines)
  2. 12,614 people out of 10 million who got Covid-19 (even if they were asymptomatic or had mild symptoms)

Whilst  an inflammation of the heart muscle (myocarditis) has been reported as a rare side effect, it is also a recognised risk from viral infections and not just Covid-19 vaccination.  Myocarditis following vaccination has however, been raised as a potential concern, although more in adolescents than adults. 

There have now been a couple of very large studies involving over 2 million people in each, so we know the risk to be between 1 to 2 people in 100,000. But importantly, the condition was either mild or moderate, responded well to treatment and no-one died from the myocarditis. 

What is the evidence that the vaccine is safe? Is there long-term safety data?

The Covid-19 vaccine trials have been the largest vaccine trials in the history of medicine, and showed safety with much more certainty than other vaccine trials.

No clinical trial can tell you the long-term effect of any drug/vaccine – this data is collected over many years. To date we are not aware of any long-term effects of vaccines from the 1990s to present day. 


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What is level of protection does vaccination give from different Covid-19 variants?

The level of protection that 2 vaccinations gave against infection from the original SARS-CoV2 virus was in the mid-to-high 90% range. We believe this is less for the Omicron variant.

However, the important thing is that the 2 vaccinations do give excellent protection against serious disease. So, although you might still get infected with Omicron, and develop Covid-19 symptoms, it is now far less likely that you will end up in hospital.

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