COVID-19 vaccine: How long immunity will last and other unknowns

More than 150 coronavirus vaccines are in development worldwide. Some headlines suggest a vaccine will be nearly impossible to create. Others say one could be widely available by the end of the year. The Oxford-AstraZeneca trial is getting a lot of attention for good results and no serious side effects in humans. 

KCRW discusses the current state of vaccine research with John Moore, professor of microbiology and immunology at Weill Cornell Medical College.

KCRW: What has the Oxford-AstraZeneca trial shown so far? 

John Moore: “There are six programs of roughly comparable stages in the Operation Warp Speed. … These trials, which are typically done on tens to low hundreds of people, they’re looking for evidence of immune responses to the vaccines, and they’re looking for safety signals or any concerns about the vaccine safety in the narrow, short-term context. 

And all of the vaccines are immunogenic, in the sense that they induce antibody and T-cell responses. And the safety signals have been generally minor … sore arms, modest fever, the kind of resolvable side effects that would not likely prevent anyone from taking the vaccine in the longer term.”

What is the difference between immunogenic and efficacy? 

“These small scale trials see whether these responses are induced in people. But they don't tell you whether those responses are protected. Because we don't know. We can’t just look at an antibody response and say, ‘Yes, that's going to protect you.’

The only way to determine protection is an efficacy trial. And that involves having up to 10,000-20,000 people. And half of them will get a fake vaccine, a placebo. And half of them will get the active vaccine. And then you measure the number of people who get infected with the virus during the trial. And you also measure in the infected people the severity of the disease. And you're looking for a difference between the active vaccine group and the control placebo group. And if there are significantly fewer infections or hospitalizations in the vaccine group, the vaccine has demonstrated efficacy.”

Then there might be a big call for mass production of these vaccines and mass inoculation. But many people are seemingly afraid that this is being rushed, and safety issues could appear later. 

“Yes, it's certainly true that vaccine safety is as essential as vaccine efficacy. We cannot use a vaccine that turns out to be unsafe. And every effort must be taken to give full public confidence in a vaccine by ensuring that it's safe. And there are procedures that will be taken and hopefully free of political interference to make sure that any licensed vaccine is both safe and effective. And the one thing that you cannot assess at this stage is: Is there any adverse intersection between the vaccine and the virus in people who become infected?

So there are examples in vaccine history of vaccines that made the disease worse because the antibody response to the vaccine increases the severity of the disease. Now, we don't see any signs of that happening with coronavirus vaccine, but you won't know for sure until an appropriate level of safety scrutiny has been given to the data. And that will take place, but it will take time. 

But it's important that that happens because the consequences for society of approving a vaccine that isn't safe will be very, very serious. So everyone's conscious of this, and procedures are in place. And it will be studied so that in the end if there is an approval and recommendations from the science and public health community, it will be based on a vaccine being both safe and effective.” 

Would you trust a vaccine that is deemed safe by the Centers for Disease Control and Prevention?

“Yeah, the CDC and the FDA and the leading government scientists, they are people that the vaccine science and public health communities have a lot of trust in. 

So we have less trust in any political interference. That would be a concern if there was an October surprise or anything … that is seen to be done for political benefit. ... But the professionals in the agencies are people who have at the forefront of their activities the safety and wellbeing of the public. So we have very strong confidence in the professional people who work for the government.”

If trial results are good, what’s the earliest availability of a vaccine for most people? 

“This gets a bit tricky because it depends on how quickly vaccines can be manufactured on very large scales. So in the normal circumstances, a company would wait for efficacy data before producing hundreds of millions of doses. Because that's a very expensive thing to do. And if the efficacy trial fails, then you've wasted the production costs of a very large amount of vaccine. 

In the context of the COVID pandemic and the urgency to shave as much time as legitimately can be done, then the government, and this is not just true of the American government, it’s also true of the U.K. and Chinese governments and European governments — are pre-funding the production of vaccines in the hope that they will be effective. So that if an efficacy signal and authorization and safety profiles are met, then the vaccines will be rolled out much quicker than would otherwise have been the case. 

And that's the sensible thing to do. It means a large amount of money being spent up front, but in the context of the economic costs of the COVID pandemic, that seems very justified. So stocks are going to be made, or probably already being made, and laid down and stored in the hope that they will be needed.”

Could a vaccine be available in spring? 

“There's a lot of fuzziness in the projections, but people are talking about early 2021 for an effective vaccine being used. … Again, rolling out a vaccine on the scale of hundreds of millions of doses worldwide is not a trivial thing. 

I mean, some of these vaccines are going to need to be stored in refrigerators. Or some of them are going to need to be stored in really cold freezers, and shipped around in refrigerated and frozen containers. And not everything could happen overnight.

And then you have debates and discussions that need to be had over who will get the first batches of vaccines. Do you go to the most vulnerable people, the older and sicker community, minority communities that have suffered greatly? Do you go to health care workers? 

And the other major unknown is how long vaccine immunity will last. Because people are used to vaccines being for life. … You get a measles vaccine as a kid, and you're literally protected for life. But that doesn't always happen. … Coronavirus immunity may be much shorter than anything to do with, say, measles. So a vaccine response may diminish in intensity after several months, and may need additional booster shots. We don't know yet.”

... This virus has only been around six months or thereabout. It's a remarkable amount of work that’s been done in a short period of time. But the one thing that money cannot buy is time. And there are things that literally just take time to do. And if you want to look at whether an antibody response lasts six months, you need six months.”

— Written by Amy Ta, produced by Rosalie Atkinson



  • John P. Moore - professor of microbiology and immunology at Weill Cornell Medicine