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7 unanswered questions about the coronavirus vaccines from Pfizer and Moderna

  • There are now two vaccine trials with promising results, but there are plenty of caveats to the good news.
  • We still don't know whether the vaccine protects against asymptomatic cases or if it even lowers the risk of spreading COVID-19.
  • The two companies behind the vaccines, Pfizer and Moderna, have yet to publish their vaccine data in medical journals, and both are pending approval by the FDA.
  • Visit Business Insider's homepage for more stories.

Two companies have now released promising results from coronavirus vaccine trials, but many questions remain unanswered.

The pharmaceutical company Pfizer announced their trial results last week, with the finding that their vaccine to be more than 90% effective at preventing COVID-19, the disease caused by the novel coronavirus.    

On Monday, upstart biotech company Moderna announced its vaccine was 94.5% effective.

Experts have lauded the efficiency of the vaccines' development, with the World Health Organization's director general calling it an encouraging "unprecedented scientific innovation" and infectious-disease expert Dr. Anthony Fauci saying efficacy rates are "remarkable."

But scientists are also cautioning that the news comes with plenty of caveats. While Moderna has released more detailed information about its vaccine than Pfizer, neither company has yet published the results of the trials, which are ongoing. 

Here are seven questions that need to be answered before the vaccines go to market.

Do the vaccines protect against both severe and mild illness?

Pfizer:

To test their vaccine, Pfizer gave 43,538 volunteers either two doses of the vaccine or two salt-water placebo injections. 

While Pfizer hasn't yet released the details on the 94 COVID-19 cases in its trial, an independent board of experts found that those who did end up contracting COVID-19 were far more likely to have received the sham shots.

It's unknown whether the vaccine protects against asymptomatic infections. Participants were only tested for COVID-19 if they experienced symptoms.

Moderna:

Moderna conducted a similar trial with 30,000 volunteers.

In the trial, 95 participants became ill with COVID-19. Only 5 of those had received the vaccine. 

Those success rates, at 94.5% and more than 90%, are far higher than the 50% effectiveness required for approval, and the 70% effective experts were hoping for. 

As with the Pfizer trial,  it's unclear whether the Moderna vaccine protects against asymptomatic infections. Participants were only tested for COVID-19 if they experienced symptoms.

It's also not clear whether the vaccine reduces the risk of severe COVID-19 cases, hospitalizations, or death, Maria Elena Bottazzi, a co-director of Texas Children's Hospital Center for Vaccine Development, told Business Insider. 

However, in Moderna's trial results, none of the participants who received the vaccine had severe illness. In contrast, among people who received the placebo, 11 out of the 90 cases were severe. 

Can the vaccines stop virus transmission?

Pfizer:

While Pfizer's seem to lower the risk of contracting symptomatic COVID-19, we don't yet know if it lowers the risk of spreading the disease. 

If, for instance, it keeps the person taking it from feeling sick or testing positive, but doesn't eliminate the contagious particles from their spit, they could be walking around unknowingly transmitting the illness to vulnerable people. 

"The moment you get a vaccine doesn't mean you're going to put your mask in the trash," Bottazzi told Business Insider. "That is not going to happen. I hope people don't think that is going to be the magic solution for all.

Moderna:

The same is true of Moderna's vaccine trial. Without specific data on asymptomatic cases and on transmission rates among people who've received the vaccine, it's hard to know whether the vaccine can prevent people from passing on the virus. 

How long will the vaccines be protective? 

Pfizer:

Pfizer's trial found the vaccine became effective 28 days after the initial dose, but only looked at how effective it remained a week after getting the second dose. 

While the company may continue following trial participants if and when emergency authorization is granted, we won't know if the vaccine confers long-term immunity for years. 

"What will be the protective efficacy over time?" Gregory Poland, director of the Mayo Clinic's vaccine-research group, said, according to the Wall Street Journal. "Is this going to be a handful of months, like the flu vaccine? Is it going to be like measles or smallpox where it's lifelong immunity?"

Moderna:

Moderna tested its vaccine's effectiveness two weeks after the second dose. But again, whether it retains its effectiveness months or years later has yet to be determined. 

What does this mean for other vaccines?

All of the vaccine candidates are designed to target the same part of the coronavirus: the spike protein that allows it to attach to and invade host cells.

Other clinical trials by AstraZeneca and Johnson & Johnson are still underway, but these preliminary successes bode well for results to come.

Read more: 'Crazy hours, short nights': The inside story of how a buzzy biotech upstart developed a potential coronavirus vaccine in record time

More vaccine options could also help fast-track the availability of the vaccine to the general public. Pfizer has said it hopes to produce 50 million doses by the end of the year, and Moderna 20 million doses. 

Is it possible to say which vaccine is best? 

Pfizer: 

Pfizer did not release detailed data from its trial, so it's too early to say which, if either, vaccine is more effective or safer. The specific results that have shown the vaccine to be more than 90% effective are among the data as yet unpublished. 

An initial limitation of the Pfizer vaccine, though, is that it needs to be kept at negative 94 degrees Fahrenheit, presenting a challenge for storage and distribution.  

Moderna:

Moderna released more details than Pfizer about its vaccine trial, including the number of COVID-19 cases among vaccine recipients compared to those who got a placebo, leading to their assessment of the vaccine as 94.5% effective. 

But it would be "naïve to compare the 90% to 94.5%," Moderna CEO Stéphane Bancel previously told Business Insider. 

The one advantage Moderna does seem to have is that its vaccine does not need to be kept at extremely low temperatures. It can be kept for up to a month in a standard refrigerator, at temperatures between 36 and 46 degrees Fahrenheit. 

When will Americans be able to get vaccinated?

Pfizer has said it hopes to produce 50 million doses by the end of the year and up to 1.3 billion doses in 2021. Moderna expects to have 20 million doses by the end of 2020, and projects 500 million to 1 billion in 2021. 

But when people will get them is the million-dollar question, Daniel Salmon, director of the Institute for Vaccine Safety at Johns Hopkins University, told Business Insider. He and other experts have said that they're waiting to see more data before jumping to conclusions about when life will return to normal.

High-risk healthcare workers and first responders should be the first in line to receive the vaccine when it's available, according to a recommendation from the National Academies of Sciences. The first phase of the plan includes vaccinating 15% of the population, also prioritizing those with two or more preexisting conditions and elderly people living in congregate care settings.

Phases 2, 3, and 4 of the plan involve rolling out the vaccine to Americans in public-facing essential jobs, such as those working in schools and grocery stores, and to older adults with risk factors who didn't make the first group.

US Health and Human Services Secretary Alex Azar last week said the Pfizer vaccine would be available to "all Americans" by April. On Monday's news briefing about Moderna's vaccine, Fauci said roll-out for Americans with pre-existing conditions will start in April.

"Even if no other vaccines were going to make it, as a worst-case scenario, I think by Memorial Day, end of June, any Americans who want a vaccine will have their hands on a vaccine," Bancel said in a video interview with Business Insider.

How safe are the vaccines, really?

Pfizer:

Pfizer did not report any serious safety concerns in their recent press release, but the company is still in the process of gathering two months of safety data to submit to the FDA. After the data are under review, information about common, short-term side effects will be public knowledge. 

However, no one will know the potential long-term side effects for a while.

Moderna:

Moderna has already reported some initial data on the side effects of its vaccine, which are significant but not life-threatening. Most were mild. The most common complaints were fatigue, experienced by nearly one in ten participants (9.7%) who received the vaccine, and muscle pain, which occurred in 8.9% of participants. In some cases, these side effects were severe enough to interfere with daily life. Other common side effects included joint pain, headaches, and pain or swelling at the injection site. 

Moderna has said the symptoms were "short-lived," but specific data has yet to be released and will be important to understanding the severity and duration of possible side effects.  

As with Pfizer, the possible long-term side effects are unknown, and it will take time to gather the data necessary to assess whether they might be an issue. 

Salmon said there's a chance that the eventual widespread vaccine rollout could result in some rare but severe reactions, so there needs to be a plan for addressing misinformation surrounding the vaccine's safety.

"There's a larger potential that if you vaccinate a lot of people quickly, a lot of bad things will happen to those people just by chance alone," he said. "If you vaccinate 30 million people over 65, you're going to have heart attacks and strokes within a day after vaccination. You need a system in place to separate coincidence from causal."

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