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Sadly, the vaccine story isn’t simple – at least not for coronavirus. And that’s because the Alpha variant – the SARS-CoV-2 strain the vaccines were created to fight – has changed.
Viruses do that. It’s part of evolution. It’s the way they survive and spread.
Just as the common flu virus changes each year, the COVID-19 virus is changing, too – fast. The Center for Disease Control and Prevention (CDC) tracks the changes with a database. As of September 2021, there have been six variants – Alpha, Beta, Gamma, Delta, Lambda and Mu. The CDC reports Delta is now the most common form of COVID-19 in the US.
Experts say the Delta virus spreads faster and causes more infections than early forms of the virus. They estimate it is two times more contagious. No one knows exactly why.
The CDC reports fully vaccinated people can be infected with the Delta virus. When this happens, it’s called a “breakthrough” infection. Those infected may not even know they have it. Others might have mild symptoms. Some may become seriously ill.
Vaccinated individuals can also spread the virus to others – although they may spread it for a shorter time. Health officials are studying current vaccines’ effectiveness against Delta.
An August 2021 study by the University of Oxford – who partnered with Pfizer to make the first approved COVID-19 vaccine – is offering insights.
Oxford researchers studied millions of PCR tests gathered from adults in the United Kingdom (UK) when Alpha was widespread. They then looked at PCR tests gathered when Delta was most common.
Their findings suggest two doses of the Pfizer and AstraZeneca vaccines work against Delta, but protection drops off over time. The Pfizer vaccine is 92% effective 14 days after a second dose. Protection fell to 90% at 30 days, 85% at 60 days and 78% at 90 days.
AstraZeneca stats were lower: 69% effective 14 days after the second dose and 61% effective at 90 days.
The study also shows when vaccinated people are infected with Delta, they carry high levels of the virus. Nearly the same as the unvaccinated. When Alpha was most common, vaccinated individuals had much lower levels of the virus than the unvaccinated. Data from Israel shows the same pattern.
The Moderna and Johnson and Johnson vaccines weren’t included in the Oxford study, but other studies have focused on their effectiveness. Although it didn’t track protection drop off, a September 2021 CDC notice reported, “Across all ages, vaccine effectiveness (VE) was significantly higher among Moderna vaccine recipients (95%) than among Pfizer-BioNTech (80%) or Johnson and Johnson (60%) vaccine recipients.
Keep in mind, all of this data is rapidly evolving.
In a statement released August 18, 2021, CDC Director Rochelle Walensky, MD, and a panel of medical experts from the U.S. Department of Health and Human Services (HHS) explained, “The current protection against severe disease, hospitalization, and death could diminish in the months ahead, especially among those who are at higher risk or were vaccinated during the earlier phases of the vaccination rollout. For that reason, we conclude that a booster shot will be needed to maximize vaccine-induced protection and prolong its durability.”
The CDC now recommends the Pfizer booster shot for some people who have completed a two-shot dose of the Pfizer vaccine. Individuals 65 and older, those in long-term care settings, people 50-64 with underlying medical conditions, and frontline workers at high risk are advised to receive the booster. The booster should be given six months after the second dose.
For those who have not yet been vaccinated, both the CDC and World Health Organization (WHO) encourage individuals to do so. “We know that our authorized vaccines prevent severe disease, hospitalization, and death from the Delta variant,” adds Dr. Walensky.