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As the second wave of COVID-19 intensifies in Canada and around the world, drug companies have been announcing the results of vaccine trials that promise to help ease restrictions and return us to pre-pandemic routines next year.
However, there is also a lot of skepticism about vaccines, as well as questions about how much trust to place in these ads. Doubt about the COVID-19 vaccine lessens as people learn more about vaccine safety testing, so these conversations are important for making informed decisions about public health. Here are some questions to consider about these vaccine study announcements.
WHAT DID THE STUDY LOOK FOR?
The 11 different phase 3 clinical trials for COVID-19 vaccine candidates each involve thousands of people receiving a vaccine or a placebo, but not knowing which one they received. When some of the participants contract COVID-19, the researchers compare the number of sick people who received the vaccine to the number of people who received the placebo.
The first announced results come from Pfizer / BioNtech and Moderna, companies that produce vaccines based on a new technology that uses a fragment of genetic instructions in a nanoparticle of fat to infiltrate living cells. Cells use a fragment of the SARS-CoV-2 spike protein as a blueprint for making virus fragments that the immune system learns to destroy. If approved, these will be the first licensed mRNA vaccines.
WHO PARTICIPATED IN THE STUDY?
An effective vaccine must reduce the risk of infection in the most vulnerable populations. COVID-19 has shown higher rates of complications and death in racialized groups, particularly in indigenous, black and Latino populations; people over 65; and people with medical conditions such as diabetes, kidney disease, and obesity. Underrepresentation in clinical trials has been a problem for years, especially for historically marginalized and exploited groups.
In the Pfizer / BioNTech vaccine study of 43,000 participants in six countries, 42% of the participants are Asian, Black, Hispanic / Latino, or Native American. Of the 30,000 participants in Moderna’s trial, 37% were from racialized and ethnic minority groups, and the study included a significant representation of people 65 and older and people with higher-risk medical conditions.
DID THE VACCINE REDUCE INFECTIONS?
The best vaccines protect against infection in 95% of people, such as measles vaccines. The influenza vaccine reduces the risk of infection by approximately 50%, which is the threshold that the United States Food and Drug Administration (FDA) set for considering authorization of a vaccine.
Pfizer / BioNTech announced a 90% reduction after the first 94 cases. The trial ended after 170 cases with a 95% reduction for people who received the vaccine, including 94% in people over 65. The Moderna vaccine showed a reduction of 94.5%. Of its 95 symptomatic cases, only five occurred in participants who had been vaccinated.
Like the Pfizer / BioNTech and Moderna vaccines, the Oxford / AstraZeneca vaccine uses a starting dose and a booster. 23,000 participants were expected to receive a control vaccine without COVID or a COVID vaccine and a booster. Due to a miscalculation, a quarter of the participants who received the COVID vaccine received a half dose followed by a full dose booster. Participants who received two full doses showed a 62% reduction in COVID cases, while participants who received half the dose before the booster showed a 90% reduction.
Because this accidental group is smaller and slightly younger, this number may not be an accurate reflection of the vaccine’s effectiveness. Of the 131 cases seen in the Oxford / AstraZeneca trial, there was a 70% reduction in people who received any amount of the COVID vaccine.
The Pfizer / BioNTech and Moderna studies relied on participants having symptoms and being tested for the virus. In the Oxford / AstraZeneca trial, some participants were regularly screened for asymptomatic infection. The different design of the study means that it is not entirely fair to compare the percentages between trials. More information is needed before we can say anything about how these vaccines affect asymptomatic infections or transmission.
DID THE VACCINE REDUCE SERIOUS INFECTIONS?
It is difficult for a COVID-19 clinical trial to demonstrate a reduction in severe disease because severe cases are less common and participants in clinical trials are generally healthy.
Pfizer / BioNTech have not yet provided information on the severity of the cases. There were 11 serious infections during Moderna’s trial that occurred in people who had not received the vaccine. In the Oxford / AstraZeneca vaccine, none of the 131 reported cases was serious. Even after these trials are completed, the numbers are still too small to say absolutely whether any of the vaccines prevent serious complications.
IS THE VACCINE SAFE?
Any vaccine that caused serious side effects in more than 10% of the hundreds of Phase 2 participants would not be able to advance to Phase 3. This means that the most common serious side effects, such as allergic reactions requiring hospitalization, are unlikely . .
Most vaccines, including many COVID-19 vaccine candidates, include additives called adjuvants that produce a stronger immune response linked to more effective and long-lasting protection. However, your stronger immune response also means that adjuvant-containing vaccines may be more likely to induce reactions such as injection site swelling and fever.
WHAT ARE THE OTHER PRACTICAL CONSIDERATIONS?
If multiple vaccines are safe and effective, we can consider other factors that affect the distribution and access to vaccination. Reporting clinical trial results use two doses per person, requiring more vaccine production and follow-up appointments, creating more barriers for the economically disadvantaged.
Some vaccines have different shipping and storage requirements. The Pfizer / BioNTech vaccine should be kept at -70 degrees Celsius, which is colder storage than most clinics and pharmacies have. Lasts up to five days in the fridge. Moderna vaccine is stable for six months at -20 degrees Celsius, one month in a refrigerator, and up to 12 hours at room temperature. The Oxford / AstraZeneca vaccine, a modified common cold adenovirus, is stable in the refrigerator for at least six months.
WHAT WE STILL DO NOT KNOW
A six-month study cannot tell us how long a vaccine will protect against the virus. This would be a question with any new vaccine, but mRNA vaccines are a new technology, which creates more uncertainty. The Pfizer / BioNTech trial was the largest, with 43,000 participants, but we cannot know if side effects occur as infrequently as one in 100,000 people. Depending on the severity of the side effects, that could change if the benefits of the vaccine outweigh the risks.
These trials also cannot tell us how willing people will be to accept a vaccine once it is approved. The effectiveness of a vaccine in improving public health depends on people taking it, which they are more likely to do when they understand the vaccine testing process. – The conversation
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