There are grounds for optimism but also several unknowns around this coronavirus vaccine

Hopes that the end of the coronavirus pandemic has become nearer have soared after the news that a coronavirus vaccine was found to be 90% effective in global trials.

Although there is definite reason to be optimistic, experts have cautioned that the data from the trials conducted by Pfizer and BioNTech are not final, and there remain plenty of unknowns.

How safe is the vaccine?
The companies have said that no “serious safety concerns” have emerged so far, but they will continue to collect data.

There are some side-effects – like a sore arm or fever – that are quite common with vaccinations, noted Paul Hunter, professor in medicine at the University of East Anglia.

Given this is a brand-new type of vaccine — one which uses technology called mRNA that hasn’t until now been approved for use in humans — it is not impossible that someone could be allergic to a component of it, he said.

Can the vaccine prevent severe disease?
The study is designed to detect whether the vaccine can protect against severe Covid-19 disease, Pfizer has said, but data has not yet been made public.

“What we can say is that the vaccine stopped clinic symptomatic infection, but there is uncertainty over asymptomatic infection,” said Hunter. “But we will hopefully learn that as we go forward.”

Logically, if you don’t get infected then you can’t get severe disease, said Dr Alexander Edwards, associate professor at the University of Reading.

Does the vaccine prevent transmission?
It is not yet clear whether or not the vaccine could protect against coronavirus infection or simply against developing symptoms once you are infected.

“If it’s stopping infection then, by definition, it should be stopping transmission from one person to another,” said Hunter.

“If you don’t get the infection because you’ve been immunised you’re not going to infect me anyway. But, if what you’re getting is an asymptomatic infection, there is still the risk potential that you could infect me, although it will almost certainly be a lot lower than if you are actually clinically ill.”

Does the vaccine work with older people and children?
Children above the age of 12 and adults aged up to 85 are included in the trial but data broken down by age has not yet been released, noted Professor Beate Kampmann, from the London School of Hygiene & Tropical Medicine.

Most vaccines do not work as well in older people, as they do in younger people. This is is not surprising as older people don’t always mount an effective immune response to a natural infection either, noted Hunter.

“So, it wouldn’t be surprising if elderly people didn’t respond as effectively as younger people to this vaccine, but that is something that we need to see the data on.”

Why doesn’t it work for 10% of people?
It’s hard to say why the vaccine didn’t work in those patients without knowing who they were, said Dr Stephen Griffin from the University of Leeds.

“The vaccine will act on different people differently. So you often get different rates of response within populations — it could be that they were all more elderly, or it could be they are from a different racial background, or it could just be that this thing only works nine times out of ten,” Griffin said.

“Until you’ve really delved down into the nitty-gritty of the data it’s hard to understand exactly why some people respond and why some don’t”

How long does protection last?
The 90% effectiveness rate was calculated seven days after the second shot, but these results are likely to change as data is collected over the longer term.

Generally, to ascertain how long protection lasts, follow up studies will be required to detect levels of both types of immune responses — antibody and T cell — as well any repeated exposure risks, Kampmann said.

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