Vaccines manufactured to protect us against the SARS-CoV-2 virus, or as we all know it, COVID-19, are highly protective. Despite this fact, the reality is no vaccine is 100% effective in preventing possible transmission. Thus, some breakthrough cases are expected, as we have seen with most vaccines. Most important, we need to remember vaccines clearly prevent serious illness and mortality.

According to the most recent report from Washington State Department of Health (DOH), there are 217 cases of COVID-19 amongst fully immunized people (received the final dose of vaccine) in the state. By definition, a person who tests positive for COVID-19 two weeks after full immunization, whether they are clinically ill or not, is called a “breakthrough case.” So far in Spokane County, 23 cases have been confirmed out of the 130,003 people fully immunized. At this time, 180,847 individuals have received at least one shot of the two-dose vaccines available.

To provide some context, it is important to look at national-level data. Approximately 7,157 cases of breakthrough infection have been identified out of more than 87 million people fully vaccinated so far. To put this in perspective, that is approximately 0.008% of fully immunized people. In Washington, the percentage is approximately 0.01%. Most of these cases have not required hospitalization, and the mortality rate at a national level is in the range of 0.0001%.

A common point of confusion with vaccines is the difference between efficacy and effectiveness. What’s the difference? Efficacy can be defined as the degree to which a vaccine can prevent disease and possible transmission under controlled circumstances. The clinical trial process that all medications, including vaccines, go through is highly controlled. People who have underlying health conditions are often immunocompromised or may be taking certain medications may not be included in a typical controlled clinical trial. In this process, vaccinated trial participants are compared to the unvaccinated (placebo) group. Efficacy can be best summarized as the percent reduction in disease incidence in a vaccinated group as compared to an unvaccinated group under optimal conditions.

Effectiveness is based on observation in the real world with the general population. In this case, people are not assigned to random groups of either vaccinated or placebo groups. The effectiveness of a vaccine translates into the ability of the vaccine to prevent the outcomes of interest in the real world. With COVID-19, the outcomes of interest are mortality and morbidity. To understand efficacy, let’s examine the Pfizer/BioNTech COVID-19 vaccine clinical trial data. During the trial, 162 people in the unvaccinated group of 21,728 were infected, but only eight people out of 21,720 vaccinated became infected. From these numbers, the research scientists calculated the fraction of people who became sick in each group.

The relative difference between both groups is the efficacy. In this case, the efficacy is 95%. This should not be interpreted as 5% of the vaccinated people would get sick; that would be over 1,000 people. It means 95% fewer vaccinated people were infected compared to the unvaccinated group.

The data for all three of the available vaccines demonstrates high efficacy levels. In preventing symptomatic disease in clinical trials, efficacy of Pfizer/BioNTech was 95%, Moderna 94%, and Johnson & Johnson/Janssen vaccine was 66% globally but 72% in the U.S. For context, the typical flu vaccine many of us get each fall has an efficacy rate of 40-60%.

With the number of COVID-19 variants increasing in the U.S., many people have questions on the performance of these vaccines. The current vaccines are expected to have a protective effect, because they elicit a broad immune response involving a range of antibodies and cells. According to recently released data from the Center for Disease Control and Prevention (CDC), both m-RNA vaccines (Pfizer/BioNTech and Moderna) are 90% effective after full (two-dose) immunization. This is based on prospective studies performed among health care personnel, first responders, and essential front-line workers. There are numerous studies in progress pertaining to this and many other areas such as efficacy in children, booster shots, etc.

The most important message to take home is vaccines work, but only if you get immunized, and if we get as many people immunized as possible. Once you are vaccinated, you need to continue following the public health guidance, facial coverings, avoid large groups particularly in poorly ventilated places, social distance and practice good hygiene including handwashing. These precautions remain necessary until our community reaches an adequate level of immunity.

If we all do this together, we will continue to manage the pandemic and get back to the people and activities we miss.

Francisco R. Velázquez, M.D., S.M., is the interim health officer for Spokane Regional Health District.