Volume 8 • 2021 • Issue 4

received one dose. This study found that vaccines were 80% effective after one dose and 90% effective after two. “The memory cells in our immune systems are primed by the first dose,” he says. “Then the effect of the vaccine is boosted by the second. I would remind people that getting their second dose is very important.” Vaccine side effects “It makes sense that people areworried about possible side effects of vaccines,” Dr. Donaldson says. “There is a lot of scrutiny of what happens to people after they are vaccinated. What I hope is that people are able to tell the difference between a known risk factor of an adverse outcome versus an increased risk of an adverse outcome.” For example, there was concern about a possible relationship between vaccination and miscarriage. It was found that miscarriage occurred in 12.6% of vaccinated people. The rate among non-vaccinated people is generally 10% to 26%. The vaccine poses no addition risk to pregnant or lactating women or their babies. In addition, according to an analysis in JAMA Internal Medicine , COVID-19 mRNA vaccines do not appear to pose any higher risk for facial paralysis than other viral vaccines. Moreover, seven cases of symptomatic acute myocarditis were reported after vaccination, but most cases were mild, there were no deaths, and patients resolved their symptoms rapidly. “The risks associated with the vaccines are very small compared with infection with COVID-19,” says Dr. Donaldson. “As hundreds of millions of people have received the vaccines that has continued to be the case.” Vaccination in teenagers In the US, hospitalization among adolescents with COVID-19 increased during March and April 2021, and one-third of hospitalized adolescents had to be treated in the ICU. Around the same time, the Pfizer vaccine proved to have an efficacy of 100% among 12–15 year olds in a phase III clinical trial that included 2,260 participants. Adolescents showed a strong antibody response to the vaccine, without serious side effects. Vaccinations have been approved for children age 12 and above in Canada. Effectiveness against variants There are four identified variants of the SARS-CoV-2 virus known as Alpha, Beta, Gamma, and Delta. Recently, Moderna designed a version of its vaccine specifically for the Beta variant and has begun phase I testing. In June, researchers in the UK and Scotland published a study that showed that the current Pfizer and AstraZeneca formulations were more than 90% effective against the Delta variant in preventing hospitalization. “I expect that because Moderna is also an mRNA vaccine, it will also be effective against the Delta variant,” says Dr. Donaldson. Combining different vaccines Common in health care in previous years, heterologous vaccination—or combining different vaccines for the same virus—has been used effectively to prevent influenza, hepatitis A, and other viruses. In fact, it may not only provide the same benefit as using one vaccine, but possibly provide an enhanced benefit. “Vaccines work by showing the immune system something that looks like a virus but really isn’t,” Dr. Donaldson says. “Using two different vaccines is like giving the immune system two pictures of the virus instead of one, maybe one face-on and one in profile. National Public Radio reporter Joe Palca suggested that metaphor, and I like it a lot.” The memory cells in our immune systems are primed by the first dose, then the effect of the vaccine is boosted by the second. I would remind people that getting their second dose is very important. Watch Dr. Donaldson’s presentation about vaccine effectiveness on CDA Oasis: bit.ly/2UAekW1 The views expressed are those of the author and do not necessarily reflect the opinions or official policies of CDA. S upporting Y our P ractice 35 Issue 4 | 2021 |