In late 2020, many people viewed the authorization and availability of vaccines against COVID-19 as a figurative light at the end of the tunnel of a dark pandemic year. Unfortunately, the end did not come as swiftly as expected. As of August 2021, just 51.5% of the United States population was fully vaccinated, falling short of the stated vaccination goal of 70%. While the number of U.S. COVID-19 cases did consistently decrease from April to June of 2021 as vaccines rolled out to the general public, a new uptick in cases began in July and quickly ballooned to pre-vaccine levels.
The primary drivers of this rise are two new viral variants of interest, Delta (B.1.6.17) and Lambda (C.37), which are spreading severe illness rapidly within unvaccinated populations as mask mandates have lifted. At the end of July, the Delta variant accounted for 83% of COVID-19 cases in the U.S., while the Lambda variant dominated throughout South America. The unique features of these variants make them primed for high transmission rates, even as communities have become vaccinated. Importantly, both variants contain similar mutations to the spike protein (L452R and L452Q in Delta and Lambda, respectively) that make antibodies roughly three times less effective at preventing infection.
Infectious disease experts are quick to point out that these outbreaks don’t mean vaccinations were for naught. Though vaccinated individuals can still experience “breakthrough” COVID-19 infections, evidence shows that vaccination does provide significant protection against severe illness and death from Delta strain infections. For example, a recent English study found that full administration of the Pfizer-BioNTech vaccine was 88.0% effective at preventing symptomatic infection from the Delta strain. As the Delta-driven surge continues in the United States, symptomatic breakthrough infections are slowly increasing, but as of August, 90-99% of those hospitalized across the country were unvaccinated. Preliminary evidence suggests that mRNA vaccine-elicited antibodies neutralize the Lambda variant and Delta variant at similar rates, suggesting that vaccines likely offer protection against severe illness and death from Lambda as well.
The high transmissibility of these variants in combination with mixed vaccination rates present a particularly challenging scenario. For example, the viral load of those infected with the Delta variant can be up to 1,000 times greater than infection with the first sequenced strain of SARS-CoV-2. Vaccinated individuals infected with Delta can still carry and shed high viral loads, but seem to be infectious for a shorter period of time than unvaccinated individuals and often experience less-serious illness that could be mistaken for allergies or a common cold—or no symptoms at all. Thus, breakthrough infections that produce minimal symptoms present a high risk of transmission to the unvaccinated.
Without other mitigation measures in place, asymptomatic spread from and among vaccinated populations is unavoidable. This is especially true as students return to school, workers return to offices, and people return to travel and other activities. Asymptomatic COVID-19 testing remains an important tool for limiting the spread of highly contagious variants like Delta. Public health officials acknowledge that the number of known breakthrough cases is likely much lower than the actual number of cases because many vaccinated and asymptomatic individuals are likely not being tested. Though vaccine boosters are on the horizon for most Americans, no one can afford to become complacent. Loosened vigilance risks the unchecked spread of current and future variants among those who will not or cannot be vaccinated, and even among those who have been. Routine asymptomatic testing for COVID-19, regardless of vaccination status, can offer critical insight into potential outbreaks before they wreak havoc in communities.
For more information on how Thermo Fisher Scientific can help you implement a COVID-19 testing program, please go to thermofisher.com/covid19.