Seven months into the pandemic, we continue to unravel the mystery that is COVID-19. There continue to be critical questions that remain unanswered.
Experts interviewed by ABC News shared five scientific mysteries that persist amid the race to end the pandemic.
This may be one of the biggest questions on the minds of many. Vaccines may be the most effective way to develop herd immunity, so that the virus can't spread effectively.
Nearly 170 vaccine candidates are being tracked by the World Health Organization. Six of these are in crucial phase three trials, where thousands are being administered vaccine doses.
Usually, vaccines take years to develop. However, optimistic projections suggest a SARS-CoV-2 vaccine could be available by the end of 2020 or early in 2021, but wide-scale distribution will take time.
"I do believe that we will be able to know if one or more vaccines is efficacious against COVID-19 by the end of year," Dr. Anna Durbin, Professor at John Hopkins Bloomberg School of Public Health, told ABC News. "I am less confident that there will be enough doses of vaccine by early 2021 to reach the at-risk populations … How this is distributed needs to be planned carefully."
MORE: Teletherapy meets teens where they live: On-screenFor the vaccine to be effective, the public would also need to be willing to be vaccinated, especially in the case of rapid "emergency use authorizations," Dr. Joseph Sakran, a trauma surgeon and public health expert at Johns Hopkins Hospital, told ABC News. "The public has to know that the vaccine being produced is safe and effective. It will be critical that the cornerstone pieces of the normal process are incorporated prior to issuing an emergency use authorization for a vaccine product."
Vaccine confidence is crucially important because enough people have to be vaccinated – estimates vary between 40-70% of the population – to enable herd immunity. Even with a perfect vaccine, distributing it to billions of people is no small feat.
In addition to problems with supply, many countries will not be able to afford enough vaccine doses.
Our understanding of coronavirus infection in children has evolved during the pandemic.
Scientists interviewed by ABC News suggest children are not infected as much as adults and with less intensity, but concerning data is coming from the Centers for Disease Control and Prevention. A recent report on COVID-19 infections in children from the CDC says that children can spread the virus effectively in certain settings. The amount of virus children shed seems to be even higher than adults.
"It's safe to say this research further complicates back-to-school planning" said Dr. John Brownstein, ABC contributor and epidemiologist at Boston Children's Hospital, adding that the CDC study, and another recent study from Massachusetts General Hospital, "confirms lack or non-specific symptoms in infected kids which makes control strategies tough" and "poses a challenge for school reopening and puts burden on testing (rather than symptom screening)."
MORE: Timeline: How coronavirus got startedThere's also a risk that some children develop an idiosyncratic, severe inflammatory reaction called Multisystem Inflammatory Syndrome in Children (MIS-C). In a small number of children, the immune system goes into overdrive and can damage the heart.
According to the CDC, we still don't know why MIS-C happens in some children. The organization highlights that "MIS-C can be serious, even deadly, but most children who were diagnosed with this condition have gotten better with medical care."
It's thought that a significant number of people with coronavirus don't get any symptoms at all, with some studies suggesting up to 80% of people are asymptomatic.
We know that there are risk factors for developing severe COVID-19: age, obesity and other co-morbidities. Ethnic minorities, especially Black and Hispanic people, are at a significantly higher risk, too.
"I think this is still such a mysterious virus … its ability to impact certain people tremendously whereas sparing others all make this virus difficult to understand, diagnose and treat," Dr. Ashish Jha, Professor of Global Health and director of the Harvard Global Health Institute, told ABC News.
There may be a genetic element at play. One study suggests two key gene variants increase the risk of severe respiratory complications, one of which is blood group. But this evidence is controversial as a more recent study by Harvard Medical School suggests that there isn't a relationship. Genetic effects are probably modest compared to the well-established risk factors.
There are two things that could influence reinfection rates; the duration of coronavirus immunity and how much the virus mutates.
However, we still don't know how long immunity lasts.
Reinfection is possible with coronaviruses causing the common cold, but did not seem to happen with SARS or MERS, which are the two other infamous coronaviruses closely related to the virus that causes COVID-19.
There have also been cases of SARS-CoV-2 infection where people test positive, then test negative, only to test positive again. This could be because of reinfection but might also because of a false-negative test result.
MORE: Doctors rebuff unproven and potentially dangerous oleander chemical falsely touted as COVID-19 'cure'Experts say that given enough time, people who have been infected with the novel coronavirus will eventually be able to be reinfected. But our experience with this virus has been so brief that they say it's unlikely, or very rare, that anyone who has survived will have been reinfected.
The unfortunate answer is probably not.
The pandemic -- the rapid, uncontrolled spread of the virus -- might end, but experts think it will continue to transmit at lower levels. This is called endemic spread. Over time, endemic viruses typically become less harmful.
The future trajectory of SARS-CoV-2 remains uncertain, but many experts predict a second peak later on in the year, before the virus becomes endemic.
Our gradual return to normality has to take into account that the virus will be with us for the foreseeable future, and we may have to brace ourselves for things getting worse before they get better. They will get better, but precisely when remains unclear.
One way scientists suggest that we can adapt to the new normal is considering the risk posed when we engage in public or in homes. Is it a low, moderate, or high-risk situation and what is the positivity rate in your community? Camping, shopping, eating at your favorite restaurant and hugging take on a different meaning. That being said, we know one answer to the question of how we beat the virus, live our lives and save many more is clear: wear our masks, watch our distance, and wash our hands.
Tune into ABC at 1 p.m. ET and ABC News Live at 4 p.m. ET every weekday for special coverage of the novel coronavirus with the full ABC News team, including the latest news, context and analysis.