By Dr. Shagufta Ali, Infectious Disease
The U.S. COVID-19 (Coronavirus disease-2019) vaccination Program began December 14, 2020. As of September 23, 2021, about 55% of the total U.S. population, have been fully vaccinated. People are considered fully vaccinated if they are ≥2 weeks following receipt of the second dose in a 2-dose series (BioNTech/Comirnaty, Moderna-mRNA vaccines), or ≥2 weeks following receipt of a single-dose vaccine (Janssen vaccine).
All COVID-19 vaccines currently approved or authorized in the United States are effective against COVID-19, including against severe disease, hospitalization, and death but with slightly lower effectiveness against the Beta, Gamma, and Delta variants compared with the ancestral strain and the Alpha variant. As of September 22, 2021, Delta is the only variant of concern (VOC) in the US (national proportion of cases > 98%), but Omicron is likely to follow.
There are four endemic coronaviruses (OC43, 229E, NL63 and HKU1), three of these viruses have probably been circulating in human populations for hundreds of years. When exposed to these viruses, immunity develops and wanes pretty quickly so it is insufficient to block reinfection entirely, but it seems to protect adults from serious illness. Whether immunity to SARS-CoV-2 will behave in the same way is so far unclear. A recent study suggests that in people infected with COVID-19, neutralizing antibodies start to decline after around 6-8 months but their immune system generates memory B cells, able to make antibodies if a new infection arises, and T cells that can eliminate virus-infected cells, when exposed. In essence, we anticipate that SARS-CoV-2 vaccines will need to be updated, possibly every year but even then, immunity from either past vaccination or infection will blunt the serious disease. Probably, the new infections will become relatively constant across years, allowing for sporadic flare-ups.
At this point, scientists are not sure how effectively vaccines can reduce transmission. If vaccines do block transmission (assuming against newer variants of the virus too), it might be possible to eliminate the virus in regions where enough people are vaccinated. A vaccine that is 90% effective at blocking transmission, will need to reach at least 55% of the population to achieve temporary herd immunity. In addition to the existing COVID-19 vaccines, hundreds are in development; including dozens in phase 3 trial. Pharma company Novavax is working on a hybrid vaccine that’s effective against both flu and COVID-19, Vaxart is working on a COVID-19 vaccine as an ingestible pill, early data showed a reduced airborne transmission of SARS-CoV-2 in animal models.
Right now, the only booster vaccine available, uses the wild type SARS-CoV2 virus — the novel coronavirus that causes the disease COVID-19, but that is not the variant causing the current or possible future surge in the U.S. Hence, some scientists, are trying to develop a multivalent vaccine by finding a common mRNA code from multiple corona viruses. This may help induce neutralizing antibodies that will be protective not only against all known and unknown SARS-CoV-2 VOCs, but also future variants of corona virus including Omicron.