The Delta variant which is currently dominating COVID-19 cases in the United States and elsewhere in the world is much more contagious than earlier strains. What's more, data from the CDC released last month suggests that vaccinated people can also transmit Delta, which wasn't thought to be the case with other variants. Two new studies released this month confirm that the mRNA vaccines are less effective than during the original clinical trials before Delta. However, Moderna's vaccine seems to offer significantly higher protection than the one designed by Pfizer/BioNTech.
Delta variant is putting a dent in vaccine efficacy, but Moderna seems to do better
All viruses evolve, undergoing mutations that can significantly change the way they spread and replicate. It's a game of chance, and after hundreds of millions of dice rolls, new variants that are more dangerous than the original coronavirus strains were bound to surface.
Scientists have identified more than 20 mutations in the Delta variant, but two may be crucial in helping it transmit more effectively than earlier strains. The first is the L452R mutation, which increases the spike protein’s ability to bind to human cells, thereby increasing its infectiousness. This mutation may also aid the virus in evading the neutralizing antibodies produced by both vaccines and previous infection. The second is a novel T478K mutation on the virus' spike protein that clings onto the ACE receptor in human cells, facilitating viral entry into the lungs.
After Delta was first identified in December 2020 in India, it quickly spread across the world and overpowered previous strains, becoming the dominant variant. By the end of July, Delta was causing more than 80% of new COVID-19 cases, according to the CDC.
The CDC further adds that Delta is more transmissible than the common cold and influenza, as well as smallpox and Ebola.
This means that people who are not vaccinated face a tremendous risk of infection and spreading the virus. The highest spread of cases and severe outcomes are happening in places with low vaccination rates, and the vast majority of hospitalizations of deaths have been among the unvaccinated.
However, this doesn't mean that vaccinated people are completely immune -- quite far from it. When an infection occurs in a vaccinated individual, doctors call it a "breakthrough case". According to the CDC, even people with “breakthrough cases” carry tremendous amounts of virus in their nose and throat, and, according to preliminary reports, can spread the virus to others whether or not they have symptoms.
According to two new reports posted in pre-print on medRxiv, Moderna's vaccine may result in fewer breakthrough cases than the product designed by Pfizer and BioNTech. An analysis of 50,000 patients from Minnesota, Florida, Wisconsin, Arizona, and Iowa registered in the Mayo Clinic Health System showed that the efficacy of Moderna's vaccine dropped to 76% in July from 86% in January. However, Pfizer/BioNTech performed much worse, its efficacy dropping to 42% in July from 76% earlier this year.
In Florida, which is currently going through its worst COVID-19 surge to date, patients fully vaccinated with Moderna had a 60% lower risk of infection than those fully vaccinated with Pfizer/BioNTech, according to the Mayo study published by inference, a Massachusetts data analytics firm.
A second study that analyzed antibodies in fully vaccinated elderly patients in an elderly care home in Ontario seems to confirm Moderna's superior protection.
"Residents administered mRNA-1273 (Moderna) mounted stronger total and neutralizing antibody responses than those administered BNT162b2 (Pfizer-BioNTech)," wrote the authors from the Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital in Toronto, Canada.
Third dose boost may be warranted soon
Taken together, these recent findings suggest that a Moderna booster shot may be necessary for those who received a Pfizer vaccine earlier this year. A third dose booster may be particularly warranted for elderly individuals.
Another study of interest that appeared this weekend analyzed vaccine efficacy from another angle by looking at how the risk of infection was affected by the elapsed time since full vaccination in Israel, one of the first countries to have the majority of its citizens vaccinated. The study involved nearly 34,000 fully vaccinated adults with Pfizer/BioNTech's product who were tested with a standard RT-PCR test between May 15 and July 26. The median time between their second dose of the vaccine and the RT-PCR test was 146 days and 1.8% of study participants had tested positive.
According to the results, the more time had elapsed since their second dose of vaccine, the higher the risk of infection, which adds further weight to the notion that a third booster shot may be required.
"In this large population study of patients tested for SARS-CoV-2 by RT-PCR following two doses of mRNA BNT162b2 vaccine, we observe a significant increase of the risk of infection in individuals who received their last vaccine dose since at least 146 days ago, particularly among patients older than 60," the authors noted.
Although the two mRNA vaccines seem to be less effective against the Delta strain compared to the original strains, fully vaccinated individuals are getting infected to a much lesser extent than unvaccinated people. Moreover, although breakthrough infections may occur, the odds of them leading to hospitalization and death among fully vaccinated individuals are very low.
An analysis of 14,019 cases of the Delta variant in England published in June showed that the Pfizer-BioNTech vaccine is 96% effective against hospitalization after 2 doses while the Oxford-Astrazeneca vaccine was 92% effective.