After emerging in Wuhan, China in late 2019, SARS-CoV-2 began to spread around the world. On March 11, 2020, the WHO declared COVID-19 to be a pandemic as the global spread of the virus began to accelerate and case numbers rose sharply in Europe, the United States, and other regions. One year later, on March 11, 2021, the numbers of cases of people infected with SARS-CoV-2 stood at about 120 million worldwide. (For up-to-date numbers, view the WHO Coronavirus (COVID-19) Dashboard). The first COVID-19 death was recorded in China in January 2020, and by September of that year the global toll had reached one million deaths. By July 2021, the number of cases approached 200 million globally, and the total recorded number of deaths surpassed 4 million.
As of July 2021, the United States had recorded the highest number of COVID-19 cases (about 34 million) and deaths (over 600,000) in the world, followed by India, and then Brazil. The United States reached a half million deaths in February 2021 - not much more than a year after the virus first emerged. This number exceeds the combined total of Americans who died from World War I, World War II, and the Vietnam War.
Beyond the illnesses and death toll, the pandemic disrupted many facets of everyday life, and resulted in school and business closures, travel restrictions, job losses and economic hardships, stressed healthcare systems, shortages of essential items, unrelated illnesses and deaths due to avoidance of routine medical care, and mental health issues. Many places have already experienced two or more surges in virus infections, and residents have had to endure restrictions on their movements.
Like other viruses, when SARS-CoV-2 replicates it makes occasional errors in copying its genetic code. Most of these mutations are insignificant. However, some of these changes can affect how transmissible or deadly the virus is or how it interacts with the human immune system. When a virus replicates in many individuals, as it does in the case in a pandemic (particularly among the unvaccinated), it becomes likelier that a virus will accumulate mutations. A subgroup of viruses that contain the same set of specific mutations is known as a variant. In addition to their scientific names, variants have been assigned Greek letters for ease of discussion.
There are multiple variants of SARS-CoV-2 circulating globally and within the United States. Currently (as of July 2021), four of these are classified by the CDC as variants of concern: Alpha (or B.1.1.7; originally detected in the United Kingdom and first identified in the United States. in December 2020), Beta (or B.1.351; first identified in South Africa and first found in the United States in January 2021), Gamma (or P.1; detected in travelers from Brazil at an airport in Japan and first detected in the United States in January 2021), and Delta (B.1.617.2; initially identified in India and first found in the United States in March 2021). In early April 2021, the Beta variant had become the dominant strain circulating in the United States, but by summer it had been largely replaced by the highly transmissible Delta variant. As of late July, the Delta variant accounted for greater than 80 percent of cases in the United States.
The reason that these particular variants are worrisome is that they are associated with higher rates of transmission, they may cause more severe disease and higher rates of death, and/or they may reduce the effectiveness of current vaccines. The presence of variants raises the possibility of reinfection, so that a person having contracted one variant of the virus could later become infected with another variant. Further concerns are that the variants may evade detection by some diagnostic tests and that they may have decreased susceptibility to therapeutic agents.
There are additional variants that are being monitored and characterized, and more variants are expected to arise. Individuals who are unvaccinated are at especially high risk of infection and serious disease from these variants.
Drugs and Vaccines
There is currently no cure for COVID-19. Clinical care consists of infection prevention and control measures and supportive care, including the use of supplemental oxygen and mechanical ventilators in cases of severe disease.
There is a limited list of therapeutic agents - for which there is evidence to show that they are effective in treating COVID-19 - that is currently available to clinicians for conditional use in patients, depending on the severity of their disease symptoms. The U.S. Food and Drug Administration (FDA) has issued Emergency Use Authorizations for anti-SARS-CoV-2 monoclonal antibodies for the treatment of outpatients with mild to moderate COVID-19. Remdesivir, an antiviral agent, is the only drug that is approved by the FDA for the treatment of COVID-19. It is currently recommended for use in hospitalized patients who require supplemental oxygen but not those that require mechanical ventilation. Dexamethasone, a corticosteroid, is recommended for hospitalized patients who require supplemental oxygen and mechanical ventilation but not those with milder disease. Additional drugs are in development and being tested. Currently, however, all of the drugs are restricted in their recommended usage to a subset of COVID-19 patients.
To date, the FDA has approved three COVID-19 vaccines for emergency use – those from Pfizer-BioNTech, Moderna, and Johnson and Johnson (J&J). All three have been demonstrated to be safe and effective. Millions of people in the United States have received COVID-19 vaccines under the most intense safety monitoring in United States history without serious side effects. Additional vaccines, including ones from Novavax and AstraZeneca, are in clinical trials or awaiting FDA approval (the vaccine from AstraZeneca has been approved for use in other countries). Although a rare and severe type of blood clot has been potentially linked to the J&J and AstraZeneca vaccines (which are based on a similar technology), these cases are extremely rare - approximately one in a million for the J&J vaccine.
The vaccines are of different types. The Pfizer-BioNTech and Moderna vaccines are messenger RNA (mRNA) vaccines and the J&J is a viral vector vaccine. All three stimulate the body to produce the SARS-CoV-2 spike (S) protein and generate an immune response against this protein, but the vaccines differ in the form in which the genetic information for the S protein is introduced into the body. None of the vaccines can cause COVID-19 or modify cellular DNA.
Although the vaccines were developed and tested and determined to be safe and effective in protecting people from COVID-19 within about a year of the emergence of the virus, the production of a sufficient number of doses and the logistics of distribution of the vaccine to the world's population has been a challenge. Ethical decisions have had to be made as to how to prioritize who should receive the limited number of doses initially available. The emergence of SARS-CoV-2 variants raises the concern that some of the vaccines could be less effective against certain variants.
A serious problem is the hesitancy of a significant proportion of the population in receiving a vaccine due to concerns about safety, misinformation about the vaccine, and other reasons. This is problematic because for COVID-19 to be brought under control, the population must achieve herd immunity. Herd immunity is when a large enough portion of the community is immune to a virus (either through natural infection or vaccination) so that the virus can no longer spread easily from person to person. This goal is most readily achieved - and with far fewer deaths - through mass vaccination than through natural infection. When herd immunity has been reached, the community is protected. This protection extends even to those who are unable to receive the vaccine, such as newborns, those who are allergic to the vaccine, and people with certain medical conditions.
The percentage of individuals who need to be vaccinated to achieve herd immunity varies from virus to virus. It is not known exactly what percentage is needed to reach this threshold for COVID-19, but experts estimate that it is in the range of 70 to 90 percent. Therefore, if enough people refuse vaccination, herd immunity will not be reached, and it would be more difficult to control the virus. Some experts suspect that COVID-19 will continue to circulate, at lower levels, for the foreseeable future.
New diseases will continue to emerge. Other coronaviruses are lurking in the wild, primarily in bats, and could again spill over into humans. Or, a different type of virus could emerge, such as another pandemic strain of influenza. Each agent brings its own challenges depending on the manner and ease with which it spreads, how serious an illness it causes, its death rate, and the fear that it provokes.
Hopefully, however, we can learn from the current pandemic that preparation, coordination, education, and attention to scientific evidence can limit the toll that a pandemic can exact. That the mRNA vaccines and viral vector vaccines approved for emergency use were developed in record time, and demonstrated to be safe and effective in preventing COVID-19, shows that this technology can be adapted to many emerging viruses once their genetic sequence is made available.