Does Hydroxychloroquine Have a Preventive Effect Against COVID-19?

In 2020, the world experienced an outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), also known as coronavirus disease 2019 (COVID-19). It is important to know that both names refer to the same disease.

COVID-19 is a new, or novel, disease. It is related to a group of known viruses. These viruses are called coronaviruses. However, COVID-19 is a new virus in the coronavirus family. At the beginning of the outbreak, there was no known medicine to treat COVID-19.1

Possible treatments for COVID-19

At the beginning of the outbreak, doctors did not have medicine to treat COVID-19. They did have some ideas of medicines that may help treat the disease. This is because doctors knew information about how coronaviruses behaved.

They also knew how they might be treated. They had studied coronavirus in lab settings. This is called in-vitro studies. Doctors and researchers had also studied coronavirus in people and animals. This is called in-vivo studies. These in-vitro and in-vivo studies helped researchers understand coronavirus.1

Antivirals and antimalarials

At the beginning of the outbreak, researchers only had the opportunity to study COVID-19 in lab settings. They discovered that antiviral drugs were somewhat effective in treating COVID-19 in the lab. They also found that some unusual drugs were able to treat COVID-19 in lab studies. These medicines included 2 antimalarial drugs, chloroquine and hydroxychloroquine.1

What is hydroxychloroquine?

Chloroquine is not available currently in the United States. Hydroxychloroquine is used to treat multiple autoimmune disorders. These include:1

Trials later showed that hydroxychloroquine is not effective in treating COVID-19 in humans. There is some evidence that it could be dangerous for some people.1

Some small trials that showed hydroxychloroquine might protect people from getting COVID-19. This effect is called prophylaxis. Doctors wanted to look at this effect on a larger scale. They needed a way to study this without giving a large number of people medicine and exposing them to COVID-19, which would be very difficult and unethical.1

Does hydroxychloroquine protect people from COVID-19?

Doctors decided to look at people who already received hydroxychloroquine for an autoimmune condition. They used data from the US Veteran’s Affairs Medical Centers (VAMC) database. This information was de-identified. This means that none of the data could be traced back to a specific person.1

The people in the study had to have been taking hydroxychloroquine for at least a year as of April 1, 2020. They had to have taken their medicines regularly and only have missed a few doses. This had to be verified by pharmacy records. They had to have a specific diagnosis of an autoimmune rheumatological-associated condition.1

Doctors compared just over 10,000 people who were taking hydroxychloroquine to almost 21,000 people who were not taking hydroxychloroquine. The people who did not take hydroxychloroquine had to have a diagnosis of an autoimmune rheumatological-associated condition as well.1

Doctors compared the 2 groups for positive COVID-19 tests and hospital admissions due to COVID-19. This included stays in the intensive care unit and deaths due to COVID 19. Both groups were checked to make sure 1 group was not sicker than the other. To make sure both groups contained people of similar health, doctors checked:1

  • Lab results
  • Other medicines people took
  • Demographics such as age, race, gender, and tobacco use

Hydroxychloroquine did not prevent participants from getting COVID-19

Doctors found that taking hydroxychloroquine did not prevent the study participants from getting COVID-19. The people taking hydroxychloroquine and those not taking both had positive COVID-19 tests at the same rate. This rate was about 3.5 cases per 1,000 people.

Doctors found that changes in the dose of hydroxychloroquine did not change the outcome. The people with high and low doses of hydroxychloroquine still tested positive for COVID-19 at the same rate.1

Study limitations

Studies like this are not perfect. While doctors can access data, they do not know all factors about a study participant’s life. They cannot guarantee that the participants are taking their medicines correctly.

They also cannot control for lifestyle factors. Are the participants exercising and eating correctly? Do they get enough sleep? Do they handle stress well? This is not data that can be found in a person’s medical chart, but it does affect their health.1

Even if we do not know lifestyle factors, this study is important. It shows how a medication can or cannot affect a person in a time when we are trying to learn as much as possible about a new disease. This data showed that we do not need to do a study about hydroxychloroquine as a preventative medicine. We already had the information. Now doctors can work to find a better medicine to prevent or treat COVID-19.1

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