Q&A: Can I still pass Covid on after I’ve been vaccinated?

The World Health Organisation estimates that vaccines prevented at least 10 million deaths between 2010 and 2015. "Many millions more lives were protected from the suffering and disability associated with diseases such as pneumonia, diarrhoea, whooping cough, measles, and polio," it says. "Successful immunisation programmes also enable national priorities, like education and economic development, to take hold."

After almost 12 months of the coronavirus pandemic, we are all hoping that 2021 will be the year when Covid-19 vaccines help the world return to some semblance of normality.

So how do the Covid-19 vaccines approved to date work?

To date the European Medicines Agency, or EMA, has approved two vaccines for use in Europe. These are the Pfizer BioNTech vaccine, named Comirnaty, and the Moderna vaccine. Both have been shown to be more than 90 per cent effective at preventing Covid-19, and safe.

They are also both mRNA vaccines, a new way of teaching the body to fight infection.

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The Covid mRNA vaccines work by instructing the cells in the body to produce the spike protein found in the virus causing Covid-19. Once our bodies produce the spike protein, our immune system recognises it as a threat and starts to build up an immune response by developing antibodies and T cells against it, a bit like what happens when we contract the virus.

But the vaccine contains only one of the 29 virus proteins, so it doesn’t make us sick; effectively, it simply tells the body how to fight Covid-19. The Covid-19 mRNA vaccines therefore protect the person who has been vaccinated and reduces their risk of contracting the virus by more than 90 per cent.

Both these vaccines need to be given in two doses, a number of weeks apart, in order to be fully effective.

Once I am fully vaccinated against Covid-19 can I still pass it on?

This is one of the many big questions that scientists are currently working on. While the vaccines protect the person who is vaccinated against disease, we still don’t know if they stop that person transmitting the virus to someone else.

Dr Anne Moore is a senior lecturer in biochemistry and cell biology in UCC with extensive expertise in vaccines and their delivery systems. According to Moore, the primary objective of current Covid-19 vaccines was to prevent disease and, while studies are still ongoing as to whether they would have an impact on transmission, it was unlikely but not impossible.

“They might prevent transmission, it’s unlikely . . . looking at it from an immune perspective, if you inject something into a muscle and into the body, you generally don’t induce a good immune response in the mucosa, in your upper airways. So, if you don’t have an immune response in your your nose and your throat, then there’s a chance that you will still harbour that virus there and you can still transmit it to other people.”

However, Moore added that we still needed to wait for the data from studies to confirm this.

Therefore, even if you are fully vaccinated, it is still not guaranteed that you will not pass the Covid-19 virus to somebody else.

This is why it is extremely important that, for now, people who have been vaccinated against Covid-19 continue to follow all the public health guidelines such as social distancing, wearing a face covering, regular hand washing, etc.

Moore said that a number of Covid-19 vaccines were currently being developed that have been specifically designed to prevent transmission. “These have been designed to induce a good immune response in the nose and throat to prevent you from getting any virus into any part of your system,” she explained.

When will we know for sure if the current Covid-19 vaccines prevent transmission?

According to Moore, it will take time before we definitively know the answer to this question. She explained that to understand if vaccines stopped transmission we would need a population-based study where you look and see if, in a vaccinated community, the level of transmission reduced.

“And that’s going to take time and again it depends on the amount of virus that is in that community after enough people have been vaccinated. In time, we can determine if virus transmission decreases when you vaccinate the majority of the population. If we reach a high level of herd immunity with these vaccines, we will also decrease the number of people who are susceptible to being infected and having disease. This will be a major milestone in combatting this virus. Time, and substantial investigation, will tell if these vaccines also have a direct or indirect effect on transmission

Speaking at a Department of Health National Public Health Emergency Team (Nphet) press briefing on Monday, January 11th, 2021, Professor Karina Butler, chair of the National Immunisation Advisory Committee with the Royal College of Physicians of Ireland and member of Nphet, said that right now vaccination was not the answer to preventing transmission. However, she added that studies were currently ongoing in this area.

How long does the protection from Covid-19 vaccines last?

Currently, much like the transmission question, we don’t know the answer to this. On the questions of how long protection lasts, Prof Butler said there was encouraging early evidence that immunity lasts perhaps six months, and maybe up to 18 months, but again this was something on which more data was needed.

A study published recently in the New England Journal of Medicine found that UK healthcare workers who had contracted Covid-19 had a significantly reduced risk of SARS-CoV-2 reinfection in the following six months.

Will the Covid-19 vaccines work against the new variants of the virus that have emerged?

In short, the answer to this question is that there is no evidence to date that the vaccines will not be effective against the new variants.

It is not unusual for viruses to change and mutate over time and multiple variants of SARS-CoV-2, which causes Covid-19, have been identified to date. However, three variants of concern have emerged as they have shown to significantly increase the transmissibility of the virus. Thankfully, to date, they have not shown to increase the severity of the disease.

These are the B117 variant also known as the UK variant, B1351 also known as the South African variant, and P1 or the Brazilian variant.

The UK variant is now widespread in Ireland and there have been three cases of the South African variant detected here. To date, there has been no cases linked to the variant from Brazil.

Dr Moore said that early data has given us reason to be optimistic that the vaccines will be effective against the new variants, as it has shown that antibodies in people who were vaccinated neutralized both the old and new variants of SARS-CoV-2.

However, as with a number of the as-yet unanswered questions on Covid-19, again with time and more data we should have a clearer response to this question. “We are optimistic that the vaccines will be effective against the new variants of the virus,” Moore said.

What impact will vaccination have on the Covid-19 pandemic?

Setting out a number of milestones or mini milestones in the fight against the pandemic, she said the first would be to vaccinate and thereby protect all healthcare workers and the medically vulnerable from disease. It removes a huge worry that the highest-risk categories will succumb to disease and be hospitalised or worse.

The next major milestone, she said, was to reach national and international vaccination coverage to form a biological barrier that would prevent the virus from spreading. Again, she said that this would take time.

In the meantime, Moore said the hope would be that the virus didn’t mutate and develop into a variant that was resistant to vaccine-induced immunity. “The best-case scenario is that we have vaccine-induced herd immunity as soon as we can,” she said.

What percentage of the population would need to be vaccinated to reach vaccine-induced herd immunity?

Moore said it was still unknown what percentage of the population of Ireland or indeed the world would need to be vaccinated to ensure this. It might also vary greatly depending on population size and environment.

However, she said that at the moment this was all theoretical and it was really important that we build up vaccine-induced immunity in the population as soon as we can. “It will happen but it will take time,” she said.

Reasons to be cheerful

The EMA is due to meet at the end of this month to give its opinion on the approval of the Covid-19 vaccine developed by AstraZeneca and Oxford University. If approved, this will be a third vaccine to add to the fight against this virus in Europe.

There are also a number of other vaccines in the pipeline at an advanced stage. GPs and pharmacists are also keen to start delivering the covid vaccine to the public and, once they start, this will greatly speed up the process.

Moore said that as more vaccinations and vaccinators came on stream and as experience grows, the rate of vaccination will increase. “If we can protect the most vulnerable, as soon as we can, that will be great and then let’s protect everybody else,” she said.