Prevention of COVID-19 and Ongoing Areas of Concern

So far, we have learned that the novel coronavirus, SARS-CoV-2, can cause severe infection and even death in a subset of people. There are some therapies being used to treat severe infection. However, the preferred way to protect people from COVID-19 is to prevent infection in the first place. SARS-CoV-2 spreads via respiratory droplets so infection prevention is similar as with other respiratory viruses like the flu or the cold. That means to stay home if you are sick, cover your mouth when you cough or sneeze, avoid touching your face, and wash your hands often. In communities with high rates of infection, there have been recommendations for social distancing.

These recommendations include, remaining at least 6 feet away from other people, as well as wearing a mask over your nose and mouth to prevent possible exposure. At the height of the pandemic, other public health measures included stay-at-home orders, closures of school, venues, and nonessential businesses, bans on public gatherings, [Advance] travel restrictions, and contact tracing and quarantining. Another important way for protecting against infectious disease is immunization, a topic Dr. Cohen covered in Immunology. One form of immunization is called Cross-reaction. This is the method Edward Jenner used with cowpox to immunize against smallpox. The COVID vaccines currently available work in a slightly different way.

On December 11, 2020, the Food and Drug Administration issued an Emergency Use Authorization for the first COVID-19 vaccine. Rather than depending on cross-reaction, this vaccine delivers messenger RNA that instructs our cells to produce viral spike protein, against which our immune system can mount a response. If we encounter viral spike protein again, such as during COVID-19 infection, we have a much better immune response. Remember, the viral spike protein is what enables the virus to enter our cells, which is a crucial step in the viral life cycle. Immunization will generate memory lymphocytes, something Dr. Cohen introduced in the “Antibodies” video.

If someone has been immunized with the COVID-19 vaccine, upon re- encountering viral antigens, for example during a viral infection, memory lymphocytes will be rapidly activated to respond to the infection. However, not all memory responses last forever. This is the reasoning behind booster shots. Many immunizations require boosters. Multiple pediatric immunizations require boosters, including the shot for measles, mumps, and rubella. Adults require repeat immunization for the tetanus, diphtheria, and pertussis toxins, or the TDaP shot. The shingles vaccine is recommended in older adults to help boost immunity against the virus that causes chickenpox which can be reactivated and cause shingles. For COVID-19, some vaccines require a series of two shots a month apart, and a booster shot 6 months later.

The hope had been that either through recovery from infection or through receiving the vaccine, more people would become immune to SARS-CoV-2 and the spread of COVID-19 would become more limited. This concept is known as herd immunity, a term that Dr. Cohen introduced in the section on immunization. However, current evidence suggests that herd immunity may not be that effective in limiting COVID-19. This is because either having disease or getting the vaccine only confers partial immunity. That is, it reduces the severity of infection but does not prevent infection. Another challenge in limiting the spread of COVID-19, is the emergence of SARS-CoV-2 variants. Just as Dr. Cohen discussed genetic drift with Influenza virus, SARS-CoV-2 can mutate rapidly.

In fact, early in the pandemic, a single base mutation changed a single amino acid. This small change altered the structure of viral spike protein. This change increased the infectivity, or the likelihood the virus could infect another person. Subsequent variants carry this mutation, but other mutations have emerged. The World Health Organization and Center for Disease Control

are tracking variants of concern: alpha, beta, gamma, delta, and as of this recording, a new one called Omicron. The mutations in these variants can potentially affect the transmissibility, severity of disease, response to therapy, and protective immunity. In an ideal immune response, antibodies neutralize the virus by binding to sites on the spike protein, thus preventing viral entry into our cells and limiting infection. [Advance] However, if the virus mutates its spike protein, it has the potential to avoid or evade effective neutralization. It’s still unclear whether people who are immune to COVID-19, either through recovery from infection or through receiving the vaccine, will be protected from infection with COVID variants.

Different strains of influenza virus circulate every season, requiring an updated yearly flu shot. It’s hard to predict what will happen for COVID-19, but companies are prepared to update their vaccines as and if it’s needed. The COVID-19 pandemic has affected nearly every aspect of our lives. We changed the way we live our day to day lives, how we go to school or work, and how we travel. There have been many deaths, and many people who have recovered from severe COVID-19 have chronic health issues. Critical illness affects more than just physical health, it can affect mental health and have lasting socioeconomic impacts.

There is still so much that is unknown, and health experts continue to learn about and respond to the lasting effects of COVID-19. I hope these videos about COVID-19 have helped you understand a little more about the biology and clinical features about SARS-CoV-2, as well as the treatments and prevention strategies used during this pandemic. I look forward to meeting with you in the next videos.