Covid 19 coronavirus: Why new vaccine is safe - your questions answered

The first batch of Covid-19 vaccine has arrived in New Zealand and is being given to front line workers. The rest of the country will follow as more doses become available - but polls show up to 30 per cent of Kiwis are still hesitant about getting the injections. Auckland University vaccines expert Dr Helen Petousis-Harris answers some of your most frequently asked questions.

How safe is the vaccine?

The Pfizer-BioNTech Covid-19 vaccine is very safe. It has been formally tested on more than 40,000 people - half received the vaccine, the other half a placebo which consisted of slightly salty water. Since it started being used widely, tens of millions of people have now received it.

In the trials, people were followed very closely for adverse events and the results between the vaccinated and unvaccinated were compared. People receiving the vaccine were more likely to experience more flu-like symptoms in the day or two afterwards and this was more noticeable after the second dose, but no events of concern were more common in the vaccine group. Regulators are keeping a close eye on one event known as Bells Palsy, which involves a temporary weakness of the face, based on excess cases in vaccinated people observed in the trials. However there are no safety concerns at this stage, as US data shows no more observed cases than expected occurring after vaccination.

Since the vaccine was approved for widespread use, safety has been monitored very closely, and in large numbers of people it becomes possible to detect very rare events. As with most vaccines, a small risk for a very severe allergic reaction called anaphylaxis was detected. The risk of this happening after the Pfizer vaccine is around 5 per million doses. It occurs within minutes of receiving the vaccine and is treated immediately by the vaccinator, who is trained to manage it. This is why people are asked to stay at the vaccination clinic for up to half an hour after vaccination - just in case.

How can we be sure it's safe?

It's fair to say there are many eyes on this. Once vaccines are deployed widely, we turn to a range of vaccine safety monitoring systems that can assess adverse events in huge numbers of people. Some of these are "sensors" that take reports of adverse events from health providers and the public. These systems can't tell you if the vaccine caused the event, but they are very good at detecting signals.

Other systems actively compare adverse events between vaccinated and unvaccinated people. Such systems can look at populations of tens of millions and tell you if vaccinated people are more at risk of a particular condition. These tools are very powerful. Two of these initiatives are multi-national, including one, the Global Vaccine Data Network, which is led by New Zealand at the University of Auckland. It includes 17 countries and a study population of around 300 million. It has the capacity to look at all Covid vaccines being used across these populations.

Helen Petousis-Harris, a New Zealand vaccinologist and Associate Professor in the Department of General Practice and Primary Health Care at the University of Auckland. Photo / supplied

Finally, regulatory agencies such as New Zealand's Medsafe are there to ensure any medicine used is safe in their population. Regulatory agencies such as the US FDA, the Australian TGA and NZ MedSafe have a very high bar for safety - they are very fussy!

Will there be side effects?

Yes, there are side effects. Some people have none and a few feel quite off-colour for a day or two. These effects are related to an immune response and people like me see them as a positive sign that you are responding to the vaccine. Of course no one wants these side effects to interfere with activities, or to make them feel unwell. By and large, these are all pretty minor and do not last long. Being even a little bit sick with Covid lasts way longer.

Also, because the Pfizer vaccine does not contain any live virus, people who have got compromised immune systems are not at risk of a live virus replicating. You cannot get Covid from these vaccines.

Hasn't it been fast-tracked?

Absolutely this has been fast-tracked. I've never seen anything like it. That is not because steps have been missed but because the layers of bureaucracy and restricted funding were removed virtually overnight and companies that normally compete with each other collaborated instead. The technology was already available. Ironically, the other thing that has helped speed things up is that there has been plenty of disease around to infect the trial participants which means you can see if the vaccine works or not in a shorter space of time. There was no shortage of people lining up to participate in the trials either. What we have seen over the last year is what is possible.

Pfizer's vaccine for Covid-19 is very safe. Photo / AP

There have been twice as many doses of Covid vaccine administered around the world than there have been Covid cases, around 200 million. Despite social media and YouTube posts, there has not been a single death attributed to this vaccine. In contrast, around 2.5 million people have lost their lives from Covid.

• Vaccinologist Helen Petousis-Harris is an associate professor in Auckland University's Department of General Practice and Primary Health Care and the Director of the Vaccine Datalink and Research Group. Since 1998 she has been involved in immunisation-related research in New Zealand, particularly on vaccine safety and effectiveness. She is co-leader of the Global Vaccine Data Network, a multinational consortium dedicated to collaboration in vaccine safety studies, and was previously the chair of the World Health Organisation Global Advisory Committee on Vaccine Safety (GACVS)