Receiving the vaccine against SARS-CoV-2 comes with a deep sense of relief. The U.S. has administered nearly 58 million doses since the COVID-19 vaccines became available in December 2020. All evidence shows that those fully vaccinated are well-protected from serious COVID-19 disease and death. One dose of the Pfizer mRNA vaccination has been reported to provide up to 85 percent protection for at least a few months, and full vaccination with two doses provides 95 percent protection against severe COVID-19 disease.
The vaccine was developed in record time, less than a year from identification of the virus, making the vaccine a marvel of clinical and basic science. It is our best defense to end a pandemic that has claimed nearly half a million lives in the U.S. As thousands of vaccines are given each day, we have taken an important step toward the goal of ending the pandemic. So, what steps remain to attain this goal?
Pandemics are global problems and the full benefit of vaccination, protection of the global community by herd immunity will not be realized until approximately 70 percent of the population is vaccinated. This will stop SARS-CoV-2 spread. Until then, the relief of being vaccinated should not translate to relaxation of mitigation procedures (masks, distancing and hand hygiene).
During most of 2020, when effective mitigation procedures could have dramatically reduced spread, serious disease and deaths, much of the U.S. neither imposed nor enforced such strategies. This happened in many other countries as well. As a result, the virus spread like wildfire. In the U.S. alone, 28 million people have been infected and spread rates remain frighteningly high.
This level of infection allows the virus to replicate trillions of times. Each replication has only a small chance of producing a variant, but given trillions of replications many variants have arisen. Variations in the viral genetic material occur randomly during viral replication. Many variants will be deleterious to the virus and not be transmitted; some will make no difference, but others may provide advantages. Variants may have increased infectivity or may escape the antibodies generated by vaccination. Such variants spread globally and quickly become the predominant contagion.
More contagious, and possibly more deadly, variants have already arisen in the UK, Brazil, South Africa and Southern California. The South African variant has proven to be more resistant to vaccine-induced immunity, as witnessed by the cessation of the clinical trial of the Oxford-AstraZeneca vaccine in South Africa because it was ineffective against the variant.
Pfizer and Moderna vaccines still maintain some efficacy against the variants that have been identified to date. The highly effective seasonal flu vaccine boasts only 40-60 percent efficacy. Since the vaccines are more than 94 percent effective, a small-to-moderate loss in efficacy still keeps the overall efficacy of the COVID-19 vaccine high in preventing severe disease. Regardless, work is in progress to modify the vaccines to better match known variants. It is essentially an arms race to vaccinate as many people as possible and stop the emergence of more problematic variants.
Modifying vaccines to match variants requires rapid sequencing of the viruses to identify, track and study emerging variants. The U.S. currently trails in sequencing efforts to identify and track variants as they emerge. However, a $200 million pledge from the Biden administration serves as a “down payment” to catch up in our attempts to track variants, modify vaccines and contain the pandemic.
In addition to the threats posed by variants, another unknown about the vaccines requires us to maintain vigilance. While the vaccines protect against severe disease and death, it is not yet known how effectively they prevent infection. In other words, vaccinated people who become infected are not expected to get sick, but they may produce low levels of viruses and spread them to others. For these reasons, the Centers for Disease Control and Prevention and public health officials recommend masking, distancing and hand hygiene after vaccination until enough people are vaccinated and the pandemic is under control. Ongoing studies will determine how well the vaccines protect against infection and transmission. It is also possible that vaccine booster shots may be necessary in the coming years to enhance immunity over time and to induce better immunity to variants.
It is essential that until we meet vaccination goals, we must remain vigilant with masking, distancing, avoiding crowds and hand hygiene, to contain the spread of variants until enough are vaccinated to control the pandemic.
James Alwine is a virologist and a fellow of the American Academy for Microbiology and of the American Association for the Advancement of Science. He is a professor emeritus at the University of Pennsylvania and a visiting professor at the University of Arizona. Felicia Goodrum Sterling is a virologist and a fellow of the American Academy for Microbiology. She is a professor and scientist at the University of Arizona.